• 

      Captain Petrilla Nurys mopped her forehead and around the collar of her uniform with her handkerchief. The long, graying braid wound up at the nape of her neck was damp, too. The radio room of the USS Colorado felt hot and cramped in the tropical waters of Kepler-69c’s Monaday Ocean. She fixed a stern gaze at the round-faced, chocolate-furred alien on the comm screen.
     “And I am telling you one last time, please have all of your personnel on the beach and ready for extraction, Healer Corkan,” she said, her tone all business. It did not impress the being on the other side of the transmission. “We are on our way to you, and time is short. We’ll only be able to surface long enough to bring you on board. We must remove you from Sokoiri. It’s going to be overrun with Hornets soon. We only have nine days before the Giliks lift, with or without us, so please be ready.”

     Humankind was so new to this interplanetary diplomacy thing. Space travel—real space travel, not a mission to the outer planets of Sol or weekend tourist trips to the Moon—was under a century old. Who could have guessed that the first time a warpknot ship had made it through a wormhole to what they called a Goldilocks planet that they’d find another intelligent species? And not just one, but half a dozen races, all with technology capable of jumping to Earth and back in a matter of weeks. A hundred years was ancient history to Nurys, but the reality still blew her mind. She had joined the Space Navy to get out there and meet aliens. She’d been a part of crews traveling on early sublight ships, but had retired to a teaching post at the Naval Academy long before that amazing first contact. Thrilled and wanting desperately to be involved, Nurys had applied for berths on the new ships, to no avail. They wanted young crew, with fast reflexes and long lifespans, just in case a warpknot cruiser broke down in the spaceways. She was thanked for her service, and advised to enjoy her retirement.

     And yet, there she was, in the same big old tub where she had done her first training rotation, the USS Colorado.

     The huge nuclear-powered sub, just a hair under 115 meters long, had been launched a century before, as part of the Virginia class of attack submarines in Groton, North America. She had seen honorable duty through a number of terrestrial battles, then retired to the naval yard at Annapolis, where she had seen class after class of cadets through their initiation into deep-space warfare. Underwater training was seen as a practical and realistic environment for learning to operate in three dimensions in full protective gear while still within easy range of breathable atmosphere. Her graduates were assigned to interplanetary and interstellar craft all over what humankind’s new allies called Earthzone.
     This ship’s predecessor, a surface battleship, had last been assigned to what was known as “magic carpet duty,” restoring service members to their families at the end of the Second World War. This ship was about to perform similar duty, sweeping noncombatants out of harm’s way. The mission would do a lot to polish humankind’s image in the eyes and other optical receptors of their new colleagues in space.

     The Lits had no means to retrieve him (Interstellar Medical Volunteer and activist Samawa, offspring of the defense minister of the Littorals) without being attacked. All their ships, and those belonging to other allied races, were easy to trace and target, thanks to the ion signature that their engines emitted. Unless they sent rowboats, the Truchs would spot the rescue craft. The enemy already suspected the Lits were going to try.
     Step forward humankind. Thanks to a recently signed treaty, Earth formed its first true alliance in space with the Littorals. The current head of Terran government had an idea. He had been in the Space Navy, and remembered his training days. Nuclear vessels didn’t create an ion trail. In other words, their technology was so old, no one was looking for it. They could pass largely unnoticed.

     Most other subs had been mothballed, decommissioned, turned into museums or broken up for salvage—but the Colorado was still in use. She was staffed up by officers who were most familiar with her, pulling in Commander Ehud Abram, an XO who was serving in the World Congress, the last class of cadets who had just graduated into the Space Navy, and Petrilla Nurys, still the training officer on duty, as captain.
     She and her fellow officers had voiced plenty of concerns about transporting the old ship into alien waters, but all analyses looked good. Surface gravity approximated Earth’s within five percent. The long, black hull strongly resembled a Deep in size and shape. Two problems: They couldn’t use ship’s sonar, because the supersonics were audible to both Deeps and Truchs; and no Terran spaceship was large enough to transport the Colorado from Earth to Monaday (Kepler-69c).

     To solve the latter problem, they approached a number of races who had little love for the Truchs. For the right price, which was to open Earth’s markets to them exclusively for six months, the Lits and humans had managed to convince a Gilik merchant to carry her there. The Giliks resembled stick insects, with prickly, ochre-yellow armor all over their bodies, and had prickly personalities to match. Roh, the captain of the Unpronounceable, or so the crew had declared it, landed just off one of Monaday’s volcanic beaches near one of those factories with a hull full of supplies for the Truchs, and to pick up raw minerals as payment.
     Under cover of night, Roh had released the Colorado into the deep, hideously polluted harbor with a warning.
     “Come back twelve sunsets! No wait!”
     Its voice grated on the ear, but Nurys took its word seriously. Twelve local days, and not a minute longer, or they’d miss their ride back to Earth. They were already three days into their journey. The turnaround was going to be rough.

     The Colorado might have an advantage with its drives, but it was handicapped with regard to its telemetry equipment. Sonar remained the most accurate, but not the only means of reading the topography. Instead of a periscope, the Virginia-class vessel was equipped with photonic sensors and infrared scopes, all passive detectors that aided in navigation. Engineers retrofitted Colorado with the latest imaging technology and a full file of 3D maps taken from space of Monaday. Running through the dark waters, Nurys wished fervently that she could ping ahead and above to see where the enemy was. The Truchs were able to use sonar and radar, running waves of pings in patterns. The enemy’s little scouts flew low reconnaissance patterns over the water, smoking anything that moved with depth charges. The Colorado’s cameras picked up little above the surface, but they had spotted numerous dead Deep floating, thanks to the trigger-happy Truchs. Colorado had to run as deep and as fast as possible, doing its best to avoid a random ping.

• 

• 

• 

• 

• 

• 

Bump! and your capsule jerks ahead one place—bump! and it jerks again, precisely like cartridges feeding into the chamber of an old-style automatic weapon. Well, that's just what we were . . . only the barrels of the gun were twin launching tubes built into a spaceship troop carrier and each cartridge was a capsule big enough (just barely) to hold an infantryman with all field equipment.

---

And clang!—it's my turn as my capsule slams into the firing chamber—then WHAMBO! the explosion hits with a force that makes the Captain's braking maneuver feel like a love tap.

Then suddenly nothing.

Nothing at all. No sound, no pressure, no weight. Floating in darkness . . . free fall, maybe thirty miles up, above the effective atmosphere, falling weightlessly toward the surface of a planet you've never seen. But I'm not shaking now; it's the wait beforehand that wears. Once you unload, you can't get hurt—because if anything goes wrong it will happen so fast that you'll buy it without noticing that you're dead, hardly.

Almost at once I felt the capsule twist and sway, then steady down so that my weight was on my back . . . weight that built up quickly until I was at my full weight (0.87 gee, we had been told) for that planet as the capsule reached terminal velocity for the thin upper atmosphere. A pilot who is a real artist (and the Captain was) will approach and brake so that your launching speed as you shoot out of the tube places you just dead in space relative to the rotational speed of the planet at that latitude. The loaded capsules are heavy; they punch through the high, thin winds of the upper atmosphere without being blown too far out of position—but just the same a platoon is bound to disperse on the way down, lose some of the perfect formation in which it unloads. A sloppy pilot can make this still worse, scatter a strike group over so much terrain that it can't make rendezvous for retrieval, much less carry out its mission. An infantryman can fight only if somebody else delivers him to his zone; in a way I suppose pilots are just as essential as we are.

I could tell from the gentle way my capsule entered the atmosphere that the Captain had laid us down with as near zero lateral vector as you could ask for. I felt happy—not only a tight formation when we hit and no time wasted, but also a pilot who puts you down properly is a pilot who is smart and precise on retrieval.

The outer shell burned away and sloughed off—unevenly, for I tumbled. Then the rest of it went and I straightened out. The turbulence brakes of the second shell bit in and the ride got rough . . . and still rougher as they burned off one at a time and the second shell began to go to pieces. One of the things that helps a capsule trooper to live long enough to draw a pension is that the skins peeling off his capsule not only slow him down, they also fill the sky over the target area with so much junk that radar picks up reflections from dozens of targets for each man in the drop, any one of which could be a man, or a bomb, or anything. It's enough to give a ballistic computer nervous breakdowns—and does.

To add to the fun your ship lays a series of dummy eggs in the seconds immediately following your drop, dummies that will fall faster because they don't slough. They get under you, explode, throw out "window," even operate as transponders, rocket sideways, and do other things to add to the confusion of your reception committee on the ground.

In the meantime your ship is locked firmly on the directional beacon of your platoon leader, ignoring the radar "noise" it has created and following you in, computing your impact for future use.

When the second shell was gone, the third shell automatically opened my first ribbon chute. It didn't last long but it wasn't expected to; one good, hard jerk at several gee and it went its way and I went mine. The second chute lasted a little bit longer and the third chute lasted quite a while; it began to be rather too warm inside the capsule and I started thinking about landing.

The third shell peeled off when its last chute was gone and now I had nothing around me but my suit armor and a plastic egg. I was still strapped inside it, unable to move; it was time to decide how and where I was going to ground. Without moving my arms (I couldn't) I thumbed the switch for a proximity reading and read it when it flashed on in the instrument reflector inside my helmet in front of my forehead.

A mile and eight-tenths—A little closer than I liked, especially without company. The inner egg had reached steady speed, no more help to be gained by staying inside it, and its skin temperature indicated that it would not open automatically for a while yet—so I flipped a switch with my other thumb and got rid of it.

The first charge cut all the straps; the second charge exploded the plastic egg away from me in eight separate pieces—and I was outdoors, sitting on air, and could see! Better still, the eight discarded pieces were metal-coated (except for the small bit I had taken proximity reading through) and would give back the same reflection as an armored man. Any radar viewer, alive or cybernetic, would now have a sad time sorting me out from the junk nearest me, not to mention the thousands of other bits and pieces for miles on each side, above, and below me. Part of a mobile infantryman's training is to let him see, from the ground and both by eye and by radar, just how confusing a drop is to the forces on the ground—because you feel awful naked up there. It is easy to panic and either open a chute too soon and become a sitting duck (do ducks really sit?—if so, why?) or fail to open it and break your ankles, likewise backbone and skull.

So I stretched, getting the kinks out, and looked around . . . then doubled up again and straightened out in a swan dive face down and took a good look. It was night down there, as planned, but infrared snoopers let you size up terrain quite well after you are used to them. The river that cut diagonally through the city was almost below me and coming up fast, shining out clearly with a higher temperature than the land. I didn't care which side of it I landed on but I didn't want to land in it; it would slow me down.

I noticed a dash off to the right at about my altitude; some unfriendly native down below had burned what was probably a piece of my egg. So I fired my first chute at once, intending if possible to jerk myself right off his screen as he followed the targets down in closing range. I braced for the shock, rode it, then floated down for about twenty seconds before unloading the chute—not wishing to call attention to myself in still another way by not falling at the speed of the other stuff around me. It must have worked; I wasn't burned.

---

Right that moment I was feeling unusually expendable, almost expended, because I was hearing the sweetest sound in the universe, the beacon the retrieval boat would land on, sounding our recall. The beacon is a robot rocket, fired ahead of the retrieval boat, just a spike that buries itself in the ground and starts broadcasting that welcome, welcome music. The retrieval boat homes in on it automatically three minutes later and you had better be on hand, because the bus can't wait and there won't be another one along.

---

A suit isn't a space suit—although it can serve as one. It is not primarily armor—although the Knights of the Round Table were not armored as well as we are. It isn't a tank—but a single M.I. private could take on a squadron of those things and knock them off unassisted if anybody was silly enough to put tanks against M.I. A suit is not a ship but it can fly, a little; on the other hand neither spaceships nor atmosphere craft can fight against a man in a suit except by saturation bombing of the area he is in (like burning down a house to get one flea!). Contrariwise we can do many things that no ship—air, submersible, or space—can do.

"There are a dozen different ways of delivering destruction in impersonal wholesale, via ships and missiles of one sort or another, catastrophes so widespread, so unselective, that the war is over because that nation or planet has ceased to exist. What we do is entirely different. We make war as personal as a punch in the nose. We can be selective, applying precisely the required amount of pressure at the specified point at a designated time—we've never been told to go down and kill or capture all left-handed redheads in a particular area, but if they tell us to, we can. We will.

We are the boys who go to a particular place, at H-hour, occupy a designated terrain, stand on it, dig the enemy out of their holes, force them then and there to surrender or die. We're the bloody infantry, the doughboy, the duckfoot, the foot soldier who goes where the enemy is and takes him on in person. We've been doing it, with changes in weapons but very little change in our trade, at least since the time five thousand years ago when the foot sloggers of Sargon the Great forced the Sumerians to cry "Uncle!"

Maybe they'll be able to do without us someday. Maybe some mad genius with myopia, a bulging forehead, and a cybernetic mind will devise a weapon that can go down a hole, pick out the opposition, and force it to surrender or die—without killing that gang of your own people they've got imprisoned down there. I wouldn't know; I'm not a genius, I'm an M.I. In the meantime, until they build a machine to replace us, my mates can handle that job and I might be some help on it, too.

Maybe someday they'll get everything nice and tidy and we'll have that thing we sing about, when "we ain't a-gonna study war no more." Maybe. Maybe the same day the leopard will take off his spots and get a job as a Jersey cow, too. But again, I wouldn't know; I am not a professor of cosmo-politics; I'm an M.I. When the government sends me, I go. In between, I catch a lot of sack time.

---

Of course, a six-platoon transport is not big compared with a battle wagon or passenger liner; these things are compromises. The M.I. prefers speedy little one-platoon corvettes which give flexibility for any operation, while if it was left up to the Navy we would have nothing but regimental transports. It takes almost as many Navy files to run a corvette as it does to run a monster big enough for a regiment—more maintenance and housekeeping, of course, but soldiers can do that. After all, those lazy troopers do nothing but sleep and eat and polish buttons—do 'em good to have a little regular work. So says the Navy.

The real Navy opinion is even more extreme: The Army is obsolete and should be abolished.

The Navy doesn't say this officially—but talk to a Naval officer who is on R & R and feeling his oats; you'll get an earful. They think they can fight any war, win it, send a few of their own people down to hold the conquered planet until the Diplomatic Corps takes charge.

I admit that their newest toys can blow any planet right out of the sky—I've never seen it but I believe it. Maybe I'm as obsolete as Tyrannosaurus Rex. I don't feel obsolete and us apes can do things that the fanciest ship cannot. If the government doesn't want those things done, no doubt they'll tell us.

Misconception #1: Orbital drops are “kickass.”

Reality: No, they f*****g aren’t. Yeah, let me just cram my up-armored ass into a tiny pod that may or may not combust in the atmosphere of the hostile planet I’m about to assault and faithfully rely on all of the sensitive electronic components that are supposed to slow me down before I pummel into the ground at terminal velocity. Contrary to popular belief, those pods aren’t designed to gently deliver you dirtside. They’re only designed to keep you alive long enough to survive skipping across the planet’s crust like a flaming pinball.

There’s no doubt in my military mind that any of the sadistic bastards who designed this drop coffin ever took a ride in one. Honestly, I think it’s purposely designed to keep us so pissed off that we’ll kill everything we see after a rough landing. The sight of enraged Marines emerging from shattered drop pods, venting puke and s*** from their exo-armor, is bound to send enemy troops fleeing.

• 

(ed note: Nexus Journal #1 PDF is for the tabletop wargame Attack Vector: Tactical. However, of general interest to military science fiction writers is a set of three articles by Claudio Bertinetto. The first is an in-depth look at the mechanics and tactics of spaceborne assault operations. This includes the logistics of transporting the army, scouting the drop zones, the D-Day drop, and advancing to the targets. The second is a detailed look at the fictional Xing Cheng Celestial Navy Marine Corps, and I mean detailed. It analyzes the various branches and missions. The third article is the Xing Cheng Table of Organization and Equipment (TO&E), which goes on for seven full pages. Any author planning an orbital drop of troops will find the information fascinating.

this is from the first article mentioned above. The analysis is about the planet of Xing Cheng {Zeta Tucanae III} performing a spaceborne assault on the planet Novaya Rossiyan {Alpha Mensae II} )

Each vehicle is loaded in an individual capsule, and then onto its carrying transport ship, a mobilized civilian freighter. The Marines drop with their trucks and AFVs, and travel on the same ships in adapted passenger pods. Six 100-ton or ten 60-ton capsules fit onto a standard cargo pod dock. The capsules themselves are automated, allowing the vehicle commander to operate them by simple commands.

---

An orbital assault is accepted by the Xing Cheng General Staff to be a one-off, extremely expensive affair. The entire brigade, including enough supplies to sustain combat for about two months, would require a minimum of 300 to 350 cargo pod docks, a sizeable portion of Xing Cheng’s civilian cargo fleet.

---

Selection of the Drop Zones would start as soon as the Fleet secures Alpha Mensae II orbit, once orbital defences have been reduced. From this phase on to the very end, the main constraint on operations will be the Heavy Zone Defense (ZD) and orbital defences around the Novaya Rossiyan capital city of Krasnograd, and Krasnaya Zezda spaceport itself.

---

As the Spaceport is the main target, yet another constraint appears: care must be taken not to damage the main launching laser, as this facility will be required to regain orbit after the invasion.

As mentioned earlier, recent CNMC doctrine states that a combat drop is far too risky to undertake close to the primary target area. Heavy ZD fire would ensure that most of the assault force would never even reach the ground. The main priority for the invasion force would thus be to determine the range of the local ZD umbrella, to ensure the landings take place outside of it.

(ed note: In the quote above they note that the invaders must take care not to damage the launching laser. But they must also keep in mind is that a laser-launch site is fuctionally equivalent to a planetary fortress. It can hurl projectiles and use laser beams directly at any invading spacecraft.

(ed note: the ships in this novel use some sort of technobabble antigravity, so they can magically make the trip from orbit to the ground and back again with no trouble.)

"Four 115-mm rifles, two fore and two aft. A pair of lift-and-drive missile launchers amidships. And a secondary gun battery of 70-mm's and 50-mm autocannon. I know the class; we captured a few of them. Good ships."

---

A week later, the ship arrived from Storisende; a hundred and sixty feet, three thousand tons, small enough to be berthed inside a hyperspace transport, and fast enough to get a load of ammunition to troops at the front, unload, and get out again before the enemy could zero in on her, and armed to fight off any Army Air Force combat craft.

---

The ship settled quickly and daintily, while Conn and Anse and Rodney Maxwell sat in the car and watched. Immediately, she began opening like a beetle bursting from its shell, large sections of armor swinging outward. Except for the bridge and the gun turrets, almost the whole ship could be opened; she had been designed to land in the middle of a battle and deliver ammunition when seconds could mean the difference between life and death.

(ed note: this is talking about assaults set in the science fictional universe of the Traveller RPG, but the author is a former member of a U.S. Army Airborne unit. So the general strategy is universal, the more detailed bits are specific to Traveller. One big difference is that in the Traveller universe, antigravity is common. There are zillions of antigravity vehicles capable of tranporting troops from surface into orbit, so extraction is usually not a problem. In other universes this is not the case, so the primary objective is to capture a planetary spaceport intact so the troops can get away.)

A blast from the past, this was originally written for Freelance Traveller in 2002! It is largely unchanged since then.

Overview

There are a number of references to planetary sieges and the taking/retaking of planets by opposing navies in the Traveller Canon, especially during the Frontier Wars. And while the Imperium mainly controls the space between the stars, there are times when the enemy isn't only in space. And while a hostile planet can be interdicted, bombed, and talked to from orbit, only troops on the ground can truly control it. This paper is my attempt to explain how I think a planetary assault would work and how one could be set up in a campaign as background, plot device, or adventure.

Assumptions and Givens

1. This is my opinion and in your Traveller universe YMMV. Much of this is based upon my knowledge of airborne operation as a former member of a U.S. Army Airborne unit.
2. I am using the Third Imperium from about the time of the Fifth Frontier War as a baseline for the assaulting force; this implies an average Tech Level (TL)-13 with a top TL-15. Switching this to other races should be relatively simple and I will include some notes.
3. I am primarily a Classic Traveller game master, but I will include references to other milieux. I hope to keep this as generic as possible.
4. I am assuming that the Imperial Army will undertake large-scale planetary actions. IMO, Imperial Marines are 'johnny-on-the-spot'; they are the visible might of the Imperium and deal with brush fires. In large-scale actions they will concentrate on 'traditional' marine roles — boarding actions and quick assaults. With 'organic' support (artillery, medical units, etc.) and heavy units the Imperial Army and its colonial units are going to be the major players in ground actions.
5. The relative superiority of near-space by the navy of the attacking force is a given. Without close orbit superiority planetary assaults are effectively doomed. This does not mean that the attacker must absolutely control close orbit, just that they must be capable of projecting great force into near orbit at specific times.
6. Specific tactics will vary based upon the tech level of the planetary forces. Against foes of TL-0 through TL-5 or so the Marines just set down in grav vehicles and move out. While a large TL-5 army with heavy support could actually mount a credible defense against TL-15 marines in battle dress, they will not prevail. At higher tech levels, however, you can face serious opposition as those large armies gain nuclear weapons and more sophisticated armor and aircraft. I have divided assault procedures into TL-6 through TL-10 and TL-10+.
7. I am taking it as a given is that military forces will generally be smaller as tech level increases. This will, of course, vary based upon law level, political stability, war footing, etc. But just as many modern armies are smaller than they were in previous generations, I am assuming that the increased efficiency of higher tech levels will reduce the number of sophonts under arms.
8. This all assumes that the attacking force actually wants to capture the planet mostly intact. If there is no interest in preserving the structures, resources, or population, I assume that a heavy orbital bombardment until the defenders were unable to resist would be sufficient.

Planetary Assaults

Objectives

A clear military objective is the key to clear military success. The ultimate goal of a planetary assault is to control the planet. In order to do this, the military objectives should be (not necessarily in order):

1. Render defending military forces unable to effectively resist ('combat ineffective').
2. Control or neutralize the defender's governmental or administrative functions.
3. Control or contain major population centers.
4. Secure means of resupply/reinforcement of attacking/occupying force.

Methods

Initially naval forces will conduct ortillery attacks against strategic targets. Defensive emplacements, command and control centers, sensor clusters, military bases, and downports will be primary targets. It is also highly likely that general infrastructure will be targeted to reduce the enemy's will to resist. Civil engineering (dams, mass transit, etc.) will be targeted. Depending on the level of resistance and the volume of ortillery fire available it is possible to reduce a planetary population to using flashlights and shipping water in trucks in a week.

The initial phase of ground assault is usually the use of drop troops (also called jump troops). Inserted from orbit, drop troops rely upon surprise, speed, and violence to secure a landing zone ('LZ'). Once secured, the landing zone is used to land heavy weapons, grav vehicles, landing ships, etc., etc. A secured LZ is called an 'orbit head'. The orbit head(s) are the start points for ground attacks against defenders and can quickly transform into the equivalent of a class C starport.

The main ground assault is performed by a mix of light and heavy infantry, mechanized infantry (infantry and g-carriers), armor, artillery, and support units. Because of the mix of units the force as a whole is called a 'combined arms army' or just 'combarm'.

Assuming the ground assault is successful, there are follow-on units that help secure the planet. Ranging from psychological warfare units to military journalists, these units strive to replace the destroyed or removed infrastructure and government of the planet with the tools of the Imperium.

 

Tactics

Although it may be unusual to think of an operation as large as attacking a planet as tactical, but to a military force capable of such an action it is. The most critical decision is; where to insert drop troops? While this should remain fluid to allow changes based upon the differences from one operation to the next, it is often very advantageous to insert an orbit head near a population center of the defenders. In addition to allowing the operation to immediately threaten defenders, it will reduce the ability of the defending military to respond with full force without endangering their own populace. The simultaneous insertion of multiple orbit heads is also preferred. This will force the defenders to split their forces and the attention of their command staff. The use of deadfall ordnance at the same time can add confusion since gravity bombs can easily be configured to 'look' like drop pods to sensors.

 

Drop Troop Insertion

The most critical period of planetary assault is the insertion of drop troops. Although supported by orbital fire the drop troops are very exposed to defenders and can suffer significant losses before reaching the ground.

To increase their chances of securing an orbit head they are accompanied by a number of tools configured to resemble troop pods to sensors.

The first such tools are 'Landing Zone Preparation Devices', also known as daisy cutters or Sylean scythes. These explosive devices are the first pods fired and are designed to mimic troop pods. About one third of these devices detonate about the LZ and use gravity lensed explosives to direct a concussive cone toward the surface. The massive overpressure is designed to detonate any mines in the LZ and knock down most plant life and structures. The remaining devices detonate on impact and are grav-focused to concentrate their force in a 3-meter high plane parallel to the surface, flattening any remaining foliage and obstacles.

The most common devices that drop amongst the troops are jammers. In addition to radio and radar jammers, there are also meaconers (devices that distort navigation signals, i.e., give false GPS results), repeaters (devices that record defenders' radio communications and repeat them over on over on a number of frequencies), and mimics (devices that send electronic and radar 'chatter' that resembles the defender's communications but give false data).

Also accompanying the drop pods on the outer fringes are defense pods. These grav-stabilized devices have radar/lidar sensors and a laser cannon, all powered by a fusion generator. These air defense systems are designed to shoot down enemy aerospace fighters, missiles, etc. Once they are on the planetary surface they will continue in this role until out of power or shut down by the drop troops.

Last but not least, each squad will have an equipment pod. The equipment will vary based upon each squad's particular mission, but will include heavy weapons, air defense systems, telecomm gear, and combat engineering tools.

Tech Levels 6 through 10

Overview

While never easy, planetary assaults against worlds at tech levels 6 through 10 are less difficult.

Defending forces do not have access to meson weapons or powered battle dress. Also, the heavier man-portable weapons are not found at these tech levels.

As mentioned above, however, a large force with the support of nuclear weapons can mount a stiff resistance. The attackers must be sure that orbiting ships can provide nuclear damper support (prevents nuclear weapons from exploding) until the drop troop can set up their own. The drop troops themselves will be optimized to repel a large number of attackers with little special attention to heavy weapons. The average trooper in battle dress with an FGMP (plasma weapon) can deal with a great many main battle tanks of a TL-8 army, after all.

The defenders will also have less sophisticated sensors, making deception more effective. Combined, these make it likely that there will be more deadfall ordnance attacks and fewer actual orbit heads (no more than one per continent, likely only one or two).

Tech Levels 11 and higher

Overview

When the defenders approach or equal the technical ability of the attacker the risks become greater.

The inherent advantage possessed by the defenders forces the attackers to take greater risks. The high mobility and concentrated firepower of high-tech forces almost compels the attacker to try and overwhelm defenses with the number of attacks.

The best option for the attacker is to release a near-flurry of troop drops and deadfall attacks combined with heavy ortillery barrages. Preparatory ortillery must especially focus on meson sites and aerospace fighter bases. The drop troops must be prepared to face a number of threats, including grav armor (antigravity tanks) and meson gun artillery.

Special Note

The use of nuclear weapons to generate an electromagnetic pulse (EMP) effect is very common during planetary assaults. Against TL-6 through 10 defenders this can be a devastating attack. And the effect against high tech opponents can be more severe than may be assumed. Although most TL-11+ electronics (especially military electronics) are shielded against EMP effects it will still temporarily overload most sensors, increasing the survivability of drop troops as they enter the atmosphere. Also, while civilian communications systems may be shielded, often their antennae are not. While the means of communication will remain intact after an EMP attack, large areas of communications blackout will exist until antennae are replaced. This will add to the fear and confusion of the defenders.

Support Operations

Intelligence

Intelligence preparation can be a critical force multiplier in planetary assaults, especially against high tech level defenses. In addition to the routine strategic intelligence gathered by Imperial Intelligence, a planetary assault requires an in depth analysis of tactical response measures, apparent willingness of defenders to endanger their own populace, and overall readiness of the defenders ground forces. Effective counter-intelligence operations can also increase the levels of tactical and strategic surprise of the attacking force.

 

Commando

Commando operations in support of a planetary assault are extremely dangerous and prone to failure. However, when they are successful they can have a considerable impact upon the defender's will and ability to fight. For these reasons, they are often popular with players. If strategic surprise can be obtained commandos can be infiltrated and supplied in a large number of ways.

Their initial targets will generally be command and control, telecommunications, and strategic defense systems. The following scenario is a demonstration of the potential impact of successful commando operations in support of planetary assault:

Three commando squads are infiltrated onto a TL-13 world in advance of a planetary assault. Arriving as workers, tourists, and ship crew, they are supplied with a full combat load, including battle dress, smuggled in by intelligence operatives. In a coordinated series of attacks, two major telecomm hubs are sabotaged by pre-set explosives, a similar attack damages the refueling facilities of the major aerospace defense center, and teams of commandos in battledress armed with FGMPs assault the members of the planetary government, planetary defense commanders, and a deep meson site (planetary fortress) that defends a section of the planet. During the resulting confusion reports are received that an enemy fleet has jumped in-system and is on vector for planetary orbit. In addition to potentially neutralizing the defender's civil and military commanders and seriously disrupting planetary defenses these actions could very well panic the defenders, degrading their ability to fight.

 

Logistics

While the first step is getting troops on the ground, the key to winning is supplying and reinforcing those troops. As soon as the orbit head is secured the follow on forces must begin to arrive. Initially these forces will be as 'heavy' as possible, i.e., g-carriers, grav tanks, and artillery pieces, preferably in large landing ships. This will be followed by a mix of combat and support units.

 

Naval

The job of the Navy is not over once the troop pods are fired. Without continued naval support the ground offensive will almost certainly fail. In addition to continued ortillery, naval aerospace fighters can provide direct close support to ground troops and engage tactical targets in the enemy's rear areas. Marines can conduct assaults against orbital facilities and can even be deployed by drop ships in support of threatened ground forces. If done properly, combined Army/Navy operations can achieve true vertical envelopment.

N-Hour Sequence

The N-hour sequence is a planning tool for military commanders, logistics planners, and political leaders. It is a rough outline of what will happen and when during a particular type of attack. The initial letter may change to determine what type of attack the sequence is for (for example, a ground attack plan can be called a G-hour sequence while a boarding action against an orbital spaceport could be an M-hour sequence). And certain times can be very broad or based entirely upon the success or failure of a different operation. They key to using an N-hour sequence is to remember that it is a tool, not the plan.

This N-hour sequence is, by necessity, abbreviated. It does not include frontier refueling, naval actions on approach to the planet, or orbital combat and boarding actions. It also omits a great many logistical steps that would be included in a 'real' sequence, as well as the preparatory steps that occur before the assault fleet enters jumpspace. Again, this is a rough estimation to give an idea of the flow of battle:

• N minus 2 weeks: Assault squadron enters jumpspace.
• N minus 1 week: Assault squadron enters normal space in target system.
• N minus 2 days: Ortillery bombardment begins.
• N minus 16 hours: Decoy deadfall ordnance attacks begin.
• N minus 8 hours: Naval aerospace fighters increase tempo of attacks against tactical surface targets.
• N minus 6 hours: Decision phase - commanders determine if planetary defenses are suppressed enough to allow close orbit insertion of drop ships. If so, drop ships move into close orbit. Bombardment ships direct their fire to both overwhelm defenders and clear a number of possible landing zones.
• N minus 2 hours: Drop troops finish insertion preparation.
• N minus 30 minutes: Decision phase - commanders determine if landing zones are prepared and the drop troops are likely to secure an orbit head. If so, drop troops are secured for insertion and troop carriers prepare for drop.
• N minus 15 minutes: Naval forces trigger EMP effects.
• N minus 5 minutes: Secondary EMP effects are triggered to disable automated responses. Naval forces begin blanket jamming from close orbit.
• N-Hour: Simultaneous insertion of drop troops begins, accompanied by numerous decoy insertions with deadfall ordnance accompanied by jammer pods. Naval aerospace fighters deploy for close air support.
• N+1 minute: Naval bombardment shifted to cover approaches to landing zones.
• N+4 minutes: Landing zone prepped by daisy cutters.
• N+5 minutes: Drop troops begin reaching surface. Drop ships begin move to high orbit.
• N+7 minutes: Drop troops begin deploying to secure orbit head.
• N+10 minutes: Drop troops finish landing on surface. Drop troops begin deployment of heavy weapons and support equipment. Aerospace fighters initiate close air support.
• N+15 minutes: Decision phase - commanders determine if orbit head is secure. If so, landing ships with armor and mechanized forces begin planetary insertion.
• N+20 minutes: Drop troops complete deployment of heavy weapons and support equipment.
• N+25 minutes: Drop troops complete initial defensive positions.
• N+35 minutes: Landing ships begin to reach the planetary surface. Mechanized and armor forces begin to deploy.
• N+45 minutes: Decision phase - commanders determine if orbit head is ready for deployment of support elements. If so, landing ships begin cycling support units and equipment to the orbit head.
• N+1 hour: Combarm begins offensive operations.

It should be obvious that the N-Hour sequence needs to be flexible. Planets with dense atmospheres will require more time for drop troops to reach the surface than planets that have no atmosphere, for example. Deployment of follow on forces may be delayed if there is a threat of significant air defense by the defenders. The number of changes that may need to be made are almost infinite. Recognizing this uncertainty, called 'the fog of war', and being able to anticipate and react to change without panic is what separates good commanders from great generals.

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This section is not really about space warfare per se, but the topic of invading a planet from space is relevant to any discussion of interplanetary strategy.

Fundamentally, there are two methods by which one can seize control of a hostile planet: conquest and capitulation.  The question is the relative costs and efficacy of the two methods.  Conquest is based upon landing troops and physically overcoming the defender, while capitulation involves bringing him to a point where he realizes that further resistance is useless.  The problem is that the conditions required for a successful landing of troops are also those required to force the enemy to capitulate through threat of orbital bombardment.  Surface defenses (see Section 4) are quite effective, and an entering drop pod is a target comparable to a modern ICBM RV.  Modern ABM weapons have proven quite successful, and there is no reason to believe that the planetary defenses of the future will do any worse.  

While the ABM debate today is outside the scope of this paper, the analogy comes up regularly, so a brief discussion is in order.  Some point to the high failure rates of current ABMs in testing as justification for describing kinetic intercepts as difficult.  Those failures are a sign of insufficient operational maturity, not of serious problems with the concept.  Other weapons systems, such as air-to-air missiles, have had similar failure rates during their early development.  India has built an ABM system using unguided missiles that fly to the predicted location of the target, and has achieved significant success, and the 1950’s era Nike Zeus achieved 59 hits during 64 tests (including a classified number of skin-to-skin hits).

When compared to an ICBM RV, a drop pod has several advantages, but also several disadvantages.  First, it is likely to be going faster than an RV at the beginning of its path through the atmosphere.  Second, unlike the RVs that most ABM systems are designed to target, the pod is likely to be headed to an area far away from the system.  Such a crossing target is significantly less vulnerable than is an approaching one.  On the other hand, anything of critical military value is likely to be protected by ABM systems, so taking advantage of this vulnerability means that the attacking force will have to move a significant distance overland to reach its objective.

The biggest disadvantage is that the pod must come to a stop before it reaches the ground, while an RV is designed to keep as much of its velocity as possible for as long as possible. A pod carrying people must also keep deceleration to a reasonable level, slowing down in the upper atmosphere.  Human tolerances for acceleration limit theoretical maximums to about 17 G if the humans in question are supine and not more than 10 G if they’re in another position.  Theoretically, these capabilities could be increased by immersing the humans in liquid, which could raise tolerances as high as 50 G, although this might require liquid breathing, familiar from several Sci-Fi works.  One issue with liquid breathing that often is ignored is the amount of stress it places on the support structure of the lungs, which are normally filled with air.  These, along with the aorta, structural failure of which is the usual cause of death under extremely high acceleration, could be surgically reinforced, but this is not a procedure that would likely be carried out on every member of an invasion force.  Even if such measures were taken, there are other problems with extremely high deceleration drops.  The biggest is probably heating, which tends to dominate atmospheric entry calculations at very high velocities, and high velocity low in the atmosphere is exactly what a high-deceleration capsule would be designed to achieve.  Equipment and structural loads are both likely to be limiting factors.  Equipment will have to be specially designed for such loads, and carefully packed for drops.  The structure of the capsules, and their heat shields, will be significantly heavier, raising transport costs significantly (discussed below).

The other significant disadvantage of a drop pod is that even a one-man drop pod will be significantly larger than an RV.  A current US RV, like the ones that carry the W87 or W88, is about 55 cm across and 175 cm long.  A human would probably need a pod at least a meter across and two meters long, or two meters across if the human is supine.  

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The actual sizing of such pods is a task which deserves more study.  For an individual pod, the best analogue is probably a 1960s project called MOOSE (originally, the acronym stood for Man Out Of Space Easiest, but it was later changed to Manned Orbital Operations Safety Equipment), which was described by its originators as a lifejacket for spacecraft.  It was a nonlifting conical body, with an empty mass of 90 kg, a gross mass of 215 kg, a diameter of 1.83 m, and a drag coefficient of around 1.42.  While advances in technology might have made the system lighter since it was originally conceived, basic physical limits (and the need to drop equipment with the personnel) mean that this remains a good representative of the minimum possible drop pod.

Sadly, details on larger pods are lacking.  While there were numerous studies of emergency return pods for either single people or groups of three people, there have been only a few studies of dropping squad-sized groups, and not at all of dropping vehicles.  The solution to this is to scale from various different types of known systems.  MOOSE, for instance, has a dry mass equal to 72% of its payload, although a larger system could probably do somewhat better.  Another interesting data point is from the airdrop rigging manual for the M551 Sheridan tank.  It suggests that the equipment for a low-velocity low-altitude airdrop is a full 20% of the mass of the vehicle.  Because of the greater structural loads involved in an orbital entry, and the need to include a heat shield, a figure in the ballpark of 60% of payload mass does not seem unreasonable.  A simple ballistic capsule might be slightly lower than this, while a more complex lifting pod will require more mass.

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The best examples of squad-sized pods are two NASA programs, the HL-20 and the X-38.  While the HL-20, with 10 occupants, was intended to be a general-purpose space vehicle, compromising its utility for comparison purposes, the seven-man X-38 was meant as a Crew Return Vehicle for the ISS, giving it a generally similar mission to the notional drop pod involved.  The HL-20 massed about 10,884 kg, with a payload of 1,815 kg, which means that the dry mass of the spacecraft is 500% of the payload mass.  The X-38 appears to have an even higher ratio, approximately 818%, although this is probably at least partially because the entire payload consisted of people, which are notoriously intensive in terms of packaging mass.  Other lifting bodies appear to have similar payload fractions, although data is quite limited.  This is a serious problem, given how important transport costs are, and the limited utility of lifting bodies in avoiding defenses.

Using code from the author’s orbits class, a number of pods were investigated (see Table 4 for characteristics).  The ballistic pods were based on pods like the MOOSE, while the numbers on the lifting pods broadly correspond to Apollo.  The characteristics of the winged pods are based on the X-38, except for payload mass fraction, which has been significantly reduced relative to said spacecraft.  No account was made of entry heating, although that would of course be a primary design driver for real-world drop pods.

Table 4

Type	Payload (kg)	Mass (kg)	Surface Area (m2)	CD	CL	BC
1-man ballistic	200	310	3	1.4	0	73.81
1-man lifting	200	350	3	1.3	0.5	89.74
1-man winged	200	1,000	5.5	0.25	0.3	727.27
12-man ballistic	2,500	3,850	18	1.4	0	152.78
12-man lifting	2,500	4,350	20	1.3	0.5	167.31
12-man winged	2,500	11,000	30	0.25	0.3	1466.67
HMMWV ballistic	4,500	6,800	30	1.4	0	161.90
HMMWV lifting	4,500	7,800	32	1.3	0.5	187.50
HMMWV winged	4,500	19,000	56	0.25	0.3	1357.14
Stryker ballistic	18,500	27,750	60	1.4	0	330.36
Stryker lifting	18,500	32,000	64	1.3	0.5	384.62
Stryker winged	18,500	77,500	125	0.25	0.3	2480.00

The most obvious result of the investigation was that ballistic pods are far inferior to either lifting or winged pods.  They must be fired into the atmosphere at very shallow angles, which means that they have long and predictable ground-tracks.  The savings in mass (and both directly and indirectly in cost) would be erased by the need to sanitize a larger corridor for the pods.  A pod capable of generating lift can use a trajectory with a steeper entry angle, using its lift to keep the deceleration at a reasonable level for a longer time, cutting down on groundtrack.  Furthermore, G-loads for ballistic capsules are relatively insensitive to variations in entry angle, and must be controlled by lowering the ballistic coefficient. This is contrary to what the analytic reentry equations would suggest, but it is due to the fact that we are not assuming entry angle to be constant.

The choice between winged and lifting pods is less clear-cut.  There is no practical difference in trajectory between the two before they reach about 50 km, where air resistance begins to build up quickly.  Above this altitude, they are vulnerable to ABM/ASAT systems, and totally unable to dodge.  Thrusters could be added to give such capability, but they would add both mass and significant expense to capsules.  This is a situation that might benefit larger pods, as there are significant economies of scale in such systems.  Below it, both become surprisingly maneuverable, capable of turning though 90° or more.  The lift vector can be altered by rolling the pod, and the choice of this direction can significantly alter the course the pod takes.  This could range from an attempt to extend the glide in the line of entry to as great a distance as possible, to a sharp turn to get ‘behind’ a heavily-defended area, to using the lift to get as low in the atmosphere as possible and keep deceleration up to get on the ground as quickly as possible.  The winged lifting body obviously has a much greater cross-range, but simply cannot slow down as quickly as a lifting capsule, because of its much lower CD and thus higher ballistic coefficient.  Most attacks would probably use lifting capsules, unless they needed to be able to maneuver around defenses low in the atmosphere.  Even then, there are serious limitations on the capability of a winged pod to maneuver after its initial bounce.  The most obvious application would be a case in which there is a narrow corridor between two sets of defenses that is too short to send pods down directly, and another corridor clear of ASAT systems that joins it at an angle.  However, this is unlikely to occur in practice, and even if it did, the attacker would have to know about it before leaving home, and then have it still be there when he arrived.  All in all, winged pods are unlikely to see significant service.

The data in Table 5 was generated with an entry interface of 150 km, and an initial velocity of 6,500 m/s, for the 1-man capsules.  The G-load was held below 10Gs.  The first scenario for the lifting and winged capsule involved the roll angle being set constantly to 0° (straight up).  The second involved the roll angle being set to 90° except in response to high G-loads, which cause it to roll towards 0°.  The third involved a 90° turn, and then attempted to hold that heading.  The last involved a complex set of control laws that was an attempt to get the capsule on the ground as quickly as possible.  Downrange is the distance from the entry interface to the final point along the spacecraft’s initial line of flight, while crossrange is the distance traveled perpendicular to the initial line of flight.  Downrange, crossrange, and duration were measured from entry interface until the pod reached an altitude of 5 km.

Table 5

	Ballistic	Simple Lifting	Simple Winged	Rolled Lifting	Rolled Winged	Turning Lifting	Turning Winged	Down Lifting	Down Winged
Entry Angle (deg)	-1.9	-8.2	-13.5	-8.2	-13.5	-8.2	-13.5	-8.1	-13.4
Downrange (km)	1460.6	1077.2	2825.9	777.2	796.2	777.3	805.1	742.0	645.9
Crossrange (km)	0	0	0	56.9	226.9	65.3	311.6	20.6	79.8
G-max (Gs)	9.95	9.91	9.93	9.99	9.99	9.99	9.99	9.98	9.98
Duration (sec)	595	669	1124	472	310	500	516	414	194

Various plots from all four scenarios are attached at the end of this section.  In all cases, the ballistic pod’s trajectory is in blue, the lifting pod’s in green, and the winged pod’s in red.  As can be seen for the simple lifting trajectory plot (figure 3), both the lifting and winged capsules bounce significantly, and the high lift to drag ratio of the winged pod carries it well downrange.  This was then countered by having the pod roll, causing the lift vector to push it to the side instead.  The resulting trajectory (figure 4) is rather interesting, as the lift of the winged body again carries it a significant distance from the initial point of impact with the atmosphere. Figure 5 shows the 3-D trajectory of the 90° turn scenario, although due to scaling of the graph, it is less obvious how much of a difference there is in crossrange.  However, the table makes it quite clear that most of the energy appears to be lost in the initial turn.  Figure 6 shows the pull-down trajectory. Table 4 clearly shows that this trajectory will get a pod on the ground fastest.  This trajectory involves the pod bleeding off most of its velocity while relatively high in the atmosphere (above 20 kilometers), then spiraling steeply down.  This could be helpful in avoiding defenses, or make the pod quite vulnerable to them, depending on type and configuration.  It might be possible, by tweaking entry angle or some other facet of pod dynamics, to get the pod deeper before it slows down, and research into trajectories has not been completed.  Due to coding limitations, the author was unable to test the effects of S-turns, but in theory there is no reason why the crossrange of an entry profile could not be reduced significantly.  

Table 6 was generated for the 12-man pods, using the same set of trajectory designs and the same constraints as used for the 1-man pods above.

Table 6

	Ballistic	Simple Lifting	Simple Winged	Rolled Lifting	Rolled Winged	Turning Lifting	Turning Winged	Down Lifting	Down Winged
Entry Angle (deg)	-1.45	-8.1	-13.4	-8.1	-13.4	-8.1	-13.4	-8.1	-13.4
Downrange (km)	1646.4	1113.5	2854.4	825.0	805.3	825.1	823.1	775.0	689.2
Crossrange (km)	0	0	0	57.3	266.4	63.5	358.0	19.4	88.5
G-max (Gs)	9.98	9.92	9.95	10.00	9.99	10.00	9.99	9.99	9.99
Duration (sec)	512	577	1058	394	311	412	486	331	178

No figures are provided for the 12-man capsules, as the trajectories are broadly similar to those of the 1-man capsules.  One of the most interesting results is the much shorter entry durations for the 12-man lifting pods, as opposed to the 1-man pods.  This is likely because of the higher ballistic coefficient of the 12-man pods increasing terminal velocity during the final phases of flight.  The much smaller difference between the winged pods is probably attributable to the same mechanism, but the lift generated by the pod makes the difference much smaller.  The 12-man pods do tend to have slightly longer downrange footprints than their smaller brethren, probably because of the same mechanism described above, in that they spend more time at higher velocities during deceleration.

Table 7 is the equivalent table for the HMMWV pods, while Table 8 is for the Stryker pods.

Table 7

	Ballistic	Simple Lifting	Simple Winged	Rolled Lifting	Rolled Winged	Turning Lifting	Turning Winged	Down Lifting	Down Winged
Entry Angle (deg)	-1.45	-8.1	-13.4	-8.1	-13.4	-8.1	-13.4	-8.1	-13.4
Downrange (km)	1651.8	1118.2	2853.0	835.5	802.7	835.6	820.5	780.5	673.9
Crossrange (km)	0	0	0	57.3	265.8	63.1	360.0	19.0	77.2
G-max (Gs)	10.00	9.94	9.93	10.00	9.99	9.99	9.99	9.99	9.99
Duration (sec)	505	564	1064	384	313	400	493	318	172

 

Table 8

	Ballistic	Simple Lifting	Simple Winged	Rolled Lifting	Rolled Winged	Turning Lifting	Turning Winged	Down Lifting	Down Winged
Entry Angle (deg)	-0.85	-8.0	-13.35	-8.0	-13.35	-8.0	-13.35	-8.0	-13.35
Downrange (km)	1898.4	1158.8	2871.8	881.6	825.6	881.1	842.8	823.5	694.9
Crossrange (km)	0	0	0	57.2	268.7	60.6	351.4	18.9	75.7
G-max (Gs)	10.04	9.95	9.96	10.00	10.00	10.00	10.00	10.00	10.00
Duration (sec)	471	492	1022	324	296	331	447	257.4	160

It should be noted that no trajectory could be found which would give the ballistic Stryker pod a trajectory that kept it under 10 G.  This appears to be a function of the very high ballistic coefficient.  The Stryker pods continue the pattern seen earlier.  Higher ballistic coefficient means shallower entry angle, longer downrange distances, and significantly shorter durations.  However, the values are similar enough that it is still probably feasible to mix them during a drop.

However, there are significant limitations to the analysis used.  While it is significantly more accurate than a simple analytic approximation, there are several causes of significant error.  First, any planetary invasion is unlikely to be of Earth.  Even if we assume that the planet is broadly Earth-like, details like local gravity and atmospheric density variations could skew the results.  Also, it assumes that aerodynamic characteristics are constant, which is false in two separate ways.  First, aerodynamic characteristics are not constant across an entire entry, although the variation with Mach number is smaller than might be expected, and can generally be ignored.  The largest variation occurs at subsonic speeds, and when an attempt was made at improved modeling, the differences were very minor.  Second, a pod could easily be designed to change its shape or angle of attack during entry to allow it to better optimize its trajectory.  An investigation of all the factors involved would require more time than the author has available.  

Note the variations in entry angle for the various trajectories.  This has a significant effect on the danger zone in which ASAT systems could attack the pod from below.  While exact orbits before entry interface were not computed, it is clear that the ballistic capsule will be vulnerable to even SM-3 and late-model THAAD-type systems from the time it is placed into its entry orbit.  The other pods will be vulnerable to such systems for approximately 1,000 km before entry interface, although the exact number will depend on the angle.  It might be possible to come in at a steeper angle and use rockets to reduce the angle at the last minute.  However, this would significantly increase the cost, mass, and complexity of the pod, and wouldn’t address the lower-altitude vulnerability issues.

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A more careful analysis of the aerodynamic data for various spacecraft reveals that there are potential shapes which could outperform the chosen Apollo-based and X-38-based pods.  A bent-bicone shape has a potential hypersonic L/D (lift-to-drag ratio) of approximately 1.4, and potentially improved packing efficiency relative to a lifting body, reducing the amount of dead mass that must be carried, and there are several other simple shapes with L/D of 0.8-1.  There exist examples of winged shapes with hypersonic L/D of as much as 2.6, although these are likely to be even heavier than the lifting body described above.

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Compared to lifting body/winged shapes, simpler conical shapes will suffer from poor subsonic aerodynamics.  The obvious solution is to use a Rogallo wing, similar to the systems originally proposed for Gemini, or a parafoil as used on the X-38.  While the Apollo capsules landed precisely enough that NASA began offsetting the point of aim from the location of the recovery ship for fear of hitting the ship, the typical miss distance was on the order of a kilometer, which requires an infeasibly large drop zone.  While this would be adequate if targeting a dry lakebed or something of the sort (water landings are impractical without support already on the surface), such features are often not conveniently placed, and Apollo did not have to worry about collisions with other descending capsules.  Modern military parafoils have L/D values of 4 to 6, which is competitive with most lifting bodies, and Rogallo wings have wide L/D values, depending on construction, ranging from 4 up to as much as 12-16, although higher L/D wings may not be particularly good for the uses under consideration here.

The original paper that described the MOOSE concept has several interesting facts relevant to landing troops on planets.  A figure on pg. 380 shows the variation in downrange distance with percentage variations in deorbit delta-V.  From a 200 nm circular orbit, a 1% variation would produce a dispersion of approximately 35 nautical miles and a 3% variation in delta-V from a 300 nm orbit will produce a 200 nm dispersion.  This is another reason to suspect that all pods will have some degree of lifting capability, to allow them to compensate not only for thrust variations during insertion, but also the other variations that may come up during the drop.  

The paper also includes a slightly less minimal design for a one-man non-lifting pod than MOOSE, as well as a 3-man lifting pod.  The ‘life raft’ (MOOSE was supposed to be a ‘life jacket’) massed about 230 kg to the 110 kg listed for MOOSE in the paper (note that these figures vary from those used in the original calculations on drop pods).  This design is not studied in great detail, as its only real advantage over MOOSE was that it didn’t have to be foamed in space, but it massed twice as much.  

A very interesting figure was included in a description of the 3-man lifting ‘lifeboat’, and is reproduced below

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V_s is the fraction of satellite velocity (or circular orbit velocity in a LEO of altitude that is not explicitly called out in the paper) the spacecraft begins to maneuver at.  The craft described began at .8V_s to reduce heating load, and a crossrange of 500 nm.  It had an L/D of 1.5, a dry mass of 1,005 kg, and a payload of 450 kg.  This is broadly similar to the winged pods described above, with a slightly worse payload fraction (although the study was conducted in the early 1960s, and better technology could improve this) and somewhat better L/D.  

An ABM system could potentially cover a substantial area.  The exact range will depend upon a number of factors, but a missile in the class of the THAAD block 4 should have a coverage footprint of approximately 300 km.  The SM-3 Block IB is estimated to have a footprint of approximately 400 km, and the Block II should be able to reach about 500 km.   These are rough estimates, but ranges on the order of 500 km are entirely reasonable for such weapons.  Unfortunately, more precise values are generally classified or otherwise unavailable, even for more mundane SAMs.  It should be noted that these are the ranges for warhead (or drop pods) landing short of the launcher.  For objects that fly over the launcher, the coverage range is much greater.  All of the listed missiles are capable of reaching low orbit, which means that the capsule could be shot at any time after it is inserted into low orbit.  It is theoretically possible to come in fairly steeply from a high orbit, but this will mean either more heating and higher deceleration forces, or very significant expenditures of delta-V to insert the capsules into their entry trajectories if they instead come in much more slowly than usual.  ABM systems are not a case where there are grounds for reasonable expectation for massive improvements in the weapons performance.  There is no propulsion system that could replace chemical rockets for the purposes of short-range missiles, and the other systems involved show no signs of significant improvement.  This is closely related to the problems seen with deep-space missiles, but made worse by the absolute requirement for high thrust-to-weight ratios.  The range is limited by the fact that the target must be shot down before it gets too low in the atmosphere for the missile to function properly.  In such cases, the radar horizon is the biggest limit on rage, and if forward-based sensors are available, range could as much as double.  Of course, radar, being an active sensor, is vulnerable to bombardment itself, and range might instead be limited by passive optical detection of entering pods.  Laserstars overhead could shoot down some of the missiles, provided that they are not being shot at themselves, but the protection they provide is almost certain to be incomplete.  That is not to say that having as many spacecraft as possible overhead during the drop is not a good idea.  At the very least, they will attract missiles that otherwise would have taken out pods.  

Even if the pods, of whatever size, have high (>1) lift to drag ratios during entry (which probably means they are lifting bodies), they still very vulnerable to missile defenses.  The pod spends a significant amount of time at altitudes above the sensible atmosphere (That part of the atmosphere that offers resistance to a body passing through it), where it has essentially no maneuverability, and would be easy pickings for any of the missiles described in Section 4.  Even after it gets lower, its maneuverability is still limited by the fact that it is unpowered, and any turns will scrub valuable energy, leaving it vulnerable to SAMs.  The best strategy is to stay entirely out of the range of defenses, which can be accomplished because of the ability of the pods to either come in at a steep angle or maneuver after entering the atmosphere.

The use of lasers against drop pods is a somewhat dubious proposition.  With proper planning of the approach, the pods will have a large thickness of atmosphere between them and the laser site, even when they are above the horizon.  A laser site will suffer from the same problems that a radar site does, as well as the issues raised by propagation through the atmosphere and potential problems penetrating the plasma shell around the pod.  This plasma would tend to absorb the laser, causing slightly more heating to the pod, but nothing more.  Even if the pod was still above the atmosphere, the fact that it has to be designed for the heating environment of atmospheric entry will mean that it will prove a significantly harder target than a conventional spacecraft.

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Other forms of hypervelocity projectile launcher are also potential candidates for use in defenses.  In theory, passive projectiles should be cheaper and much harder to detect.  The exact velocity achievable is a complicated question.  In theory, most systems should be capable of significant velocities, probably more than a typical ABM.  However, there are significant drawbacks to firing projectiles at such speeds.  It is likely that high velocity flight at such low levels will produce a plasma trail would give away the projectile, and might well be hard on the surroundings.  The other drawback is that unlike a typical missile launcher, the launcher is expensive, and potentially vulnerable.  This is likely to make them a less-attractive option for planetary defense, with the possible exception of ram accelerators, which do not require a sophisticated launcher.  The ram accelerator might also be able to repurpose the projectile into a conventional ramjet for sustainer work during atmospheric flight.

The efficacy of individual drop pods is highly doubtful, however.  Even if only minimal losses are suffered, there are still the problems encountered during the airborne landings in Normandy on D-Day.  Troops were scattered, and most of the airborne forces spent their time wandering about as small groups of men from different units instead of fighting as formed units.  This type of confusion drastically reduces combat effectiveness.  It could be argued that maneuvering drop pods could place troops closer together, but at the speeds involved in spaceflight timing errors of a second can scatter pods by 7 km or more.  

Another significant problem with individual pods is the lack of heavy equipment for the troops on the ground.  Anything that is in a pod larger or heavier than a man will be both an easier target and a more prominent one, and a mass-optimized equipment pod will follow a different trajectory from a mass-optimized individual pod.  The defense would likely shoot at such pods on general principal, denying the drop units support.  Even if some way were found to combat the dispersion problem, light casualties could still compromise combat effectiveness significantly.  Even losses as low as 10% can have a significant effect on the combat power of a unit, particularly an airborne unit that has had most of its vehicles destroyed.

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Some people would raise powered armor as the solution to this problem.  After all, if an infantryman can be given the firepower of a vehicle, there is no need for vehicles.  The problem with that is that there is virtually no reason to expect that practical powered armor will be developed in the PMF (Plausible Mid-Future).

First, we must define powered armor.  Powered armor is a suit that provides the infantryman with greater strength and protection than an unarmored infantryman while not interfering with his function as an infantryman.  The last part is critical.  The armored infantryman must still be able to do the jobs required of infantry, such as clearing buildings and going up stairs.  This in turn sets size and weight limits on the armor.  Current OSHA guidelines state that the design load for stairs is 510 lb.  Even assuming that all of that limit is available (ignoring things like old or rotten stairs, or stairs not built to code), an average combat-loaded modern infantryman (sans armor) still weighs approximately 225 lb., leaving 285 lb. available for the armor.  This number includes not only the armor itself, but also all of the various servos and power supplies necessary to run it.  As an example, the Lockheed HULC currently weighs 53 lb. without batteries and can carry about 200 lb.  However, it is only a lower-body system and must include its own structure, so given various developments, a total of 50 lb. for the entire power/servo system does not seem entirely out of the realm of possibility.  This leaves 235 lb. for armor.  Taking as a baseline current ESAPI (Enhanced Small Arms Protective Insert) plates, this translates to about 35 square feet of armor or 3.2 m².

A typical adult male has a surface area of 1.9 m², so this is a vaguely practical number for armor area once all the other stuff under the armor is taken into account.  The ESAPI plates are rated to resist WWII-vintage M2 .30 caliber armor-piercing rounds, but only when backed by the various plate carrier vests.  This means that the total surface area available would have to drop again, which in turn reduces the practicality of the system.  Even then, more modern 7.62 mm AP ammo would likely be able to defeat it, although solid information on this is difficult to find.  At one point, rifles in this caliber were standard-issue, and could be again if a need (such as defeating targets in powered armor) was there.  Such an evolution of weapons to counter increased armor has happened before.  In the 1500s, the standard gunpowder weapon was called an arquebus, and it was incapable of penetrating the increasing thicknesses of armor being worn on the battlefield.  A heavier gunpowder weapon, called the musket, was developed to defeat such armor.  Muskets made armor more or less obsolete, and once they had done that, they shrank to the size of the arquebus, absorbing it in the process.  

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Increasing the weight of armor protection to defeat such threats moves the armor out of the category of “powered armor” and into the realm of “small vehicle”, which has the side-effect of removing the operator from the infantry.  As a friend of the author’s said “if you plan on having your infantry armed like tanks, and armoured like tanks, you shouldn't be surprised that they weigh as much as tanks.”  The small vehicles that would result have no parallel in modern warfare, casting doubt on their utility, and even if they were to prove useful, it is likely that they would not look like powered armor, due to the complex actuators and control systems required of such armor.  A small tracked or wheeled vehicle with a turret would be much more efficient, although it has been pointed out that it might also look quite a lot like a Dalek.

All of the above analysis assumes modern armor and weapons, and the assumption for application to the PMF is that the balance between armor and weapons will remain more or less constant.  This could obviously be flawed, but even if armor increases in power relative to weapons, the weapons used will be tailored to deal with the threat.  Small (~25 mm), low-power weapons that fire shaped charges would probably be effective if all else fails, absent special authorial pleading.  

The above is a best-case analysis. There are likely to be other complications from powered armor, such as reduced mobility (a problem in urban combat), increased ground pressure (a problem anywhere there is mud), increased logistics burden (a problem anywhere) and the fact that not all steps are built to OSHA specs.  The combat load of a soldier will also likely increase, and the number used above was for a basic rifleman only.  Grenadiers in the study referenced carried an extra 8.5 lb, and SAW gunners an extra 16 lb, to say nothing of the heavy weapons personnel, or even personnel who are simply heavier than average.  Add to this the fact that powered armor, both in fiction and in real life, is often touted as not only protecting the soldier, but also increasing his carrying capacity.  All of these combine to render powered armor a dubious proposition.  This is not to say that exoskeletons will not be useful for increasing the carrying capacity of soldiers, or that powered armor might not have a role in peacekeeping/counterinsurgency operations, where the enemy does not have access to modern weapons.  The problems of reliability and maintenance will also be major issues for a force that relies so much on very high-tech equipment.  Without real-world experience, it is difficult to determine how much maintenance powered armor would require, but even the most basic powered armor will be very complex compared to virtually all systems the infantry use today.  This is not a good thing when the system will be exposed to dirt, mud, debris, insufficient maintenance, and near-continuous use.  This in turn indicates that additional maintenance facilities above and beyond what is standard today will have to be dropped with the unit, exposing them to the orbital defenses (see above).

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An alternative is to drop a more conventional mechanized unit, complete with vehicles.  This unit will tend to land in bigger chunks, improving effectiveness, but the reduced number of targets for the defenders is likely to result in greater losses.  Unless all pods are of the same mass, the defenders will still be able to discriminate between them, and guess at their payloads.  This would likely allow them to focus their attacks on bigger, heavier pods, which could be assumed to carry things like tanks.  Careful design of a unit’s equipment could mitigate this problem, but only at a cost in mass-efficiency for both the pods and the equipment.  The exact tradeoff is heavily technology-dependent, and thus outside the scope of this paper.

In either case, once the attackers are on the ground, they still have to move to their target and capture it.  The movement in question will be over hundreds if not thousands of kilometers of terrain, and impeded by enemy resistance, terrain features, and a lack of roads.  If the drop zone was a relatively undefended area, it was probably also lightly inhabited, and thus lacking in transportation infrastructure.  Sabotage would also contribute to this lack, delaying the advance even more.  The US Army estimates that a typical rate of march (including rest and maintenance halts) of between 16 and 32 km/h depending on the quality of the roads and the time of day, with a practical maximum daily range of approximately 200 km.  Note that this is for a road march in peaceful conditions, not a combat advance.  Even the “high-speed” advances in the 2003 Iraq War averaged somewhere around 15 km/h, against light opposition.  However, taking the average daily range and a distance of 1000 km (through some combination of landing distance and not being able to take the shortest route), the unit will take 5 days to reach the target.  This does not take into account the possibility of resistance, and the various problems that could occur during what will be at least a semi-tactical march.  During this period, the enemy will know where they are, and where they are going, and be able to move forces to reinforce the objective.  It seems reasonable that the defender will be able to manage at least twice the attacker’s movement rate, giving a huge radius in which troops can be drawn from to reinforce the defenses.  This assumes that the landing zone is a complete surprise to the enemy, which is unlikely to be the case if any serious preliminary bombardment is done.  For that matter, extended preliminary bombardment might be counterproductive, giving an enemy the warning he needs to move local defense systems in to slaughter the drop pods.  These systems could be small and relatively-low performance, resembling modern SAMs, as they would only have to intercept the pods at low speed and altitude.

Once the assault force arrives at the target, they must overwhelm the troops defending it.  Assuming that the attacking force has about three times the per-man effectiveness of the defenders (which is not unreasonable, as training masses nothing and making equipment better is often cheaper than shipping more of it), they will need about even numbers to overcome them.  This ignores potential losses in effectiveness due to fatigue, losses in key personnel, and general confusion during the drop and march.  Training, equipping, transporting and supplying that many troops is going to get expensive very fast.

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 Exactly how expensive is an interesting question.  Taking as our baseline a Stryker Brigade Combat Team (chosen because it seems a reasonable analog to a future space-transportable unit with integrated support units), the total mass of vehicles and heavy equipment is at least 12,025 tons (time and information constraints prevented a better number, although this estimate was intended to be a reasonably conservative best-case).  There are a total of 4,236 men, and assuming that light equipment and people amounts to 500 kg per man, the total “combat mass” comes to at least 14,145 tons.  There are roughly 1500 individual vehicles/pieces of heavy equipment, so at least that many drop pods are required (assuming crews drop with their vehicles).  If we assume 4.5 kg/man/day shipboard, the unit requires 572 tons/month in transit.

The combat supply requirements are somewhat more involved.  The first assumption made is that all water is being procured on the surface, instead of being dropped from orbit.  The second is that the vehicles do not require fuel, and use some form of lightweight power source, which is likely to be ultimately nuclear-derived.  A typical man-day’s supply will total 31.8 kg (of which 14.2 kg is ammo and 6.8 kg is equipment attrition replacements), with an additional 24.4 kg if the vehicles use shipped fuel.  This totals 134.7 tons/day of combat, although this number may be low (the source value for supplies/man/day probably includes higher-echelon troops than are present in the SBCT and who don’t use as much ammo as those on the front lines).  After major combat operations are completed, the daily requirements will drop to around 13 kg/man/day, or 55.1 tons/day, which can be reduced by another 1.8 kg/man/day if food is procured locally.

If combat is expected to take 30 days, then the total supply requirements will be 4,041 tons.  This will also have to be dropped, for a total drop mass of 18,186 tons.  However, this number ignores the mass of the fuel systems that would need to be deployed.  While the paper referenced above contains some details on the proposed scheme, details on the exact weights involved are fairly sparse.  Reference is made to the system breaking even for weight with gasoline after 30 days of combat.  If this is correct, then the mass required for the fuel production system would be approximately 3,100 tons, or about 17% more drop mass.  However, the report in question dates back to the early 1960s, and it is likely that the technology of the future (or even of today) would allow significant reductions in that mass, although how significant is impossible to estimate precisely.  An assumption of a fuel system mass of 1,000 tons is probably as reasonable as is possible without detailed study, bringing the drop mass to 19,186 tons (assuming that no additional personnel above and beyond the brigade’s normal complement are required to operate the machinery).

Assuming that the drop pods have a total mass equal to 50% of the payload (which is a somewhat generous, but generally in line with the numbers given above), that means a total drop pod mass of 9,593 tons.  It might be possible to reduce the drop pod mass slightly by finding more mass-efficient ways to drop supplies, such as reusable shuttles.  However, this does require improved security around the drop zone, and planners would probably assume that this would generally not be the case.  Also, we need to account for supplies consumed during transit.  If we assume a total transit time of 6 months, this mass (which does not have to be dropped) will amount to 3,432 tons.  The total mass that must be launched into space for this mission is a minimum of 32,211 tons.  The troops will probably require at least 3 tons/man in hab space (keeping in mind that they must be fit to fight at the other end), so the total hab mass is a further 12,708 tons, although a fair bit of this can probably be provided by requisitioned civilian ships, and would not be included in the launch budget.  Assigning a further 10% of payload mass for general spacecraft structure, the total payload mass that must be moved from one planet to another is approximately 49,411 tons.  This is a total of 11.7 tons/man, of which 7.6 tons must be launched specifically for this mission.  Even if launch costs approach current grid energy costs ($100/3.6 GJ, which is theoretically possible if using laser launch, a space elevator, or a launch loop), the cost of putting the necessary equipment and personnel in orbit will be $26.84 million.  If the transit velocity is about the same as orbital velocity, the transit energy cost will be $82.34 million; although a more realistic number for such a transit would be twice that (the above ignores the energy costs of the ships themselves).  Given the other costs of running a spacecraft, the total shipping bill for the brigade could easily pass $300 million in even the most optimistic case.  This totally ignores the costs of the drop pods and supplies themselves, although the cost of supplies for transit can be traded off against the energy cost of using a faster, higher-energy transit.

To move multiple brigades, which will be required for all but the smallest worlds, many times the amount of stuff described above will have to be moved, to say nothing of the various combat support elements.  Heavy artillery, combat support, and air units will all need drop pods, habs, and cargo spacecraft.  The shipping bill alone would rapidly rise into the billions or tens of billions of dollars, and the heavy equipment is more vulnerable during the drop.

Training the forces is also non-negligible.  It is likely that the troops would need to be trained in an environment that has the characteristics of the target world.  The best way to do this appears to be an orbital hab with a rotation rate set to give the appropriate gravity.  Terrain can probably be approximated at home, and the hab can have an appropriate atmosphere.  The spin rate of a power’s habs might be an important piece of intelligence data to back up signs of preparations for an invasion, giving an indication of who they expect to go to war with.

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At this point, it would be logical to suggest the use of robots as an alternative to human troops, and there are significant factors to recommend this approach.  A robot not would require habs during shipping, would (presumably) take no training, and could be considered expendable.  However, there are problems with this approach, as it rests on the assumption that a suitable ground-combat robot could be created.  Many of the reasons cited in Section 2 in support of unmanned warships do not apply on the ground.  The largest issue is that while it is practical to propose that every spacecraft be run by remote control, doing the same for a robotic invasion force removes entirely the logistical advantages accrued therein.  This in turn requires the creation and deployment of autonomous robots in an environment that is tactically far less clean than space, overcoming formidable technical and moral/political obstacles.  Nor should the difference in physical environment be overlooked.  A robot would have to deal with dirt, mud, and other hazards of military life with little maintenance, as well as being capable of fulfilling all the roles of the person it is replacing, in an environment where versatility is far more important.  The cost of this is non-trivial, although it does offer a vaguely-plausible alternative for those willing to imagine that robotics will advance so far.

Another, often overlooked issue with robots is their effectiveness in replacing humans during counterinsurgency operations.  A robot advanced enough to be effective at winning hearts and minds is unlikely to be the cheap and disposable device described above.  Morally, it will have to be almost equivalent to a person to win the trust of those it works among, which more or less erases the line between robot and human, except from a logistical perspective.  And the overall logistical requirements of a robot-based force are unlikely to be that much better than an equivalent human-based one.

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If the landing were to take place, it would be the attacker’s ultimate gamble.  All of his troops would be landed in one area, and there is no practical way to get them back.  Laser launch and robust SSTOs would offer the capability to evacuate some of the men, but all of the heavy equipment would probably have to be abandoned.  Even such an evacuation would be risky, as the defender would want to trap as many men as possible, if for no other reason than to make it more difficult to attack again later.  Any spacecraft taking off would do so through a barrage of missiles, and laser launch sites would be prime targets for any number of different methods of attack.

If the attacker made a successful landing, he would have to face the defender’s surviving forces.  One major advantage the defender has is that not only does he not have to pay shipping costs for his units, he can also use quantity to overcome quality.  Most of the defender’s army would be draftees, given a few months of training and some basic weapons.  One on one, the attacker’s units would have no problem destroying them thanks to better training and equipment.  However, they do not have to pack as much combat power into as little mass as possible, which allows them to be deployed in large numbers at the optimum ratio for cost to combat power.  Furthermore, they are on the defensive, which is less difficult for the inexperienced troops that make up the majority of their ranks.

One alternative to a serious invasion is to stage a change of government to one that is more favorable to you.  This can either be done by encouraging a coup, or by supporting an insurgency.  The coup would be encouraged by threats against the planet if the planet does not surrender, along with promises of good treatment if it does.  Insurgency holds great story potential.  Small teams would be inserted onto the planet, probably through normal space travel, and used to create or support local guerilla movements, with the aim of overthrowing the government.  This is not practical in all situations, as it either requires a weak government (which might not be able to resist a conventional attack), a large existing insurgent movement, or a great deal of both patience and luck.

It has been suggested that the costs of effective space forces and orbital defenses are large enough that a defender cannot field sufficient ground forces to effectively resist an invasion.  The problem with this is that ground forces are relatively cheap, and sufficient forces to make invasion very difficult can be funded out of the leftovers from the Navy.  As mentioned above, the defender’s equipment can be designed to be as cheap and reliable as possible, and stockpiled well before the battle.  Furthermore, unless the potential attacker is very close to the defender’s planet, the long lag between the invasion force departing home (when it is detected) and landing on the defender’s planet would allow the Army to normally exists as a cadre with stockpiled equipment, further reducing operating costs.

Local irregular units might supplement the defender’s conventional forces.  The efficacy of this type of force in harassing conventional units has been demonstrated in Iraq and Afghanistan in recent years, and their effectiveness is multiplied many times over by the fact that the attacker is racing against the clock imposed by his supplies and the defender’s response.

All of the above discussion assumes a homogenously-defended world, which no allies for the attacker.  If there are any allies, the situation changes significantly.  The best option in that case is simply to ship the men to the ally, and buy the equipment and supplies from him, or just pay him to make the attack in the first place.  Even if some special equipment has to be shipped in, a large proportion of the vehicles in any large military unit are simple trucks, or slightly more complex variations on generic vehicles.  All supplies should be procured on-planet, as tooling up to make munitions is generally much simpler than making vehicles.

The problem with this plan is that the potential target is unlikely to fail to notice the preparations and will strenuous, and probably violently, object.  Also, any power on a balkanized world will have a much stronger army than one that is in control of a homogenous world, all else equal.  The best way to invade is probably by using the ally as a proxy.  However, if, for whatever reason that is not practical, the invader would probably have to fight through any orbital defenses the defender would have, with the ally presumably joining in.

Orbital defenses of Balkanized worlds are a very complicated matter, with the potential for battles between various sets of orbital defenses.  There is the possibility that the world will have a more-or-less unified set of orbital defenses, similar in concept to NORAD.  The problem is that if the powers are close enough to set something like that up, they are unlikely to turn on each other to the extent of supporting an invasion.  More likely, each power will have its own orbital defense system, which, being in orbit, has global coverage, preventing the attacker from going around it, as well as ground-based defenses in their own territory.  It would also have the secondary purpose of destroying the orbital infrastructure of any of the other powers that attack it.  Supporting an invasion (even if not as an active participant) is a de facto act of war, so the off-planet attacker would somehow have to protect his ally in the opening stages of the war.

Even after the orbit-based defenses are destroyed, the fact that the defenses are limited to their own territory does not necessarily mean that the attacker will be safe on the other side of the world.  Today, many nations hold small islands scattered around the world, which would make ideal bases for such defenses.  The defensive submarines mentioned in Section 4 would also be ideal for a balkanized world, particularly as the attacker might well have to exercise more restraint in hunting them for fear of hitting neutrals.

The best way to use an ally might be merely as a staging point.  The attacker would come in on his own at first, and attempt to gain space superiority. The other power(s) on the planet would be induced to declare neutrality, and when the orbital battles were over, any allies would declare for the attacker and probably conduct the bulk of the invasion themselves, with the aid of limited orbital fire support and possibly occupation troops.  At the same time, the defender would surely figure out what’s coming, and probably would declare war preemptively.  The only way to make an alliance work is if the extraplanetary attacker was somehow able to pre-position his forces without the target being overly suspicious.  Deployments of ground troops might be concealed under the pretense of joint training missions, although the logistics of shipping them to the target planet makes this approach problematic.  A more likely scenario is a port visit by a naval squadron of some sort.  Provided that such visits happen regularly, it is possible that an attacker and his local ally could gain a very significant advantage in orbit.

The defender can still make life complicated and landings difficult even if the attacker has a planetary ally.  As noted in Section 4, surface defenses have very long ranges, and it is entirely possible that a defender could hit targets over an attacker’s ally.  This would make landing troops difficult even with an ally, or force the attacking force to move a significant distance overland.  While this is probably preferable to the dangers of an opposed landing, even administrative movements are difficult and slow.  There are also likely to be prepared border defenses that would have to be dealt with, a problem that would be avoided if they were landing directly in the enemy’s territory.

In many ways, the easiest scenario for a ground invasion is a planet that is not homogenously defended, but also not balkanized, so there are few or no surface defenses in place.  The attacker can land away from the defenses and move overland to attack the target.  The biggest problem is likely to be transportation.  As mentioned above, areas that are poorly defended are likely to be of little consequence and have poor transportation infrastructure.

Assuming that a method besides a straight-up invasion is chosen, the attacker will of course have to move some ground troops to be able to occupy the planet after it has surrendered.  The analysis of moving a ground force provided above applies, but the problems for occupation troops are less severe.  First, the supply load for occupation troops is approximately a third of that of troops in combat, and might be reduced farther by the transportation of small factories or the use of local industry.  Second, the drop pods can be replaced with conventional surface-to-orbit shuttles.  The first units would probably land in pods, but follow-on ones would be landed at no mass penalty.  Third, the units themselves can be equipped differently than they would be for facing military units.  This could result in substantial mass savings, as heavy vehicles like tanks can be left behind.  The exact employment of the occupation force is outside the scope of this paper, but there are numerous works on the subject.

All of this begs the question of why exactly the attacker wants the world.  An attempt to add to one’s territory is probably best accomplished through diplomatic means, possibly backed up by some display of military force.  Resources are plentiful enough that, barring McGuffinite (plot-dictated special resources), invading a planet for them is not a sensible plan.  The exception to that rule is humans, but in that case, the defender will probably fight to the bitter end rather than accept slavery.  However, if humans are the target, invading a low-tech world is by far the most sensible plan.  Another possibility is the world itself.  If habitable worlds are rare (moving somewhat outside the PMF) then conflict over them is a possibility, but the question then becomes why the attacker would not use a bioweapon instead, wiping out the population and leaving the infrastructure (and probably the biosphere) unharmed?  The most likely answer is that bioweapons are viewed as abhorrent and use of them gives one the status of an outlaw state, combined with the potential problems of the agent either surviving to render the planet uninhabitable or escaping to other worlds.  If the population is more important than the infrastructure, bombarding the infrastructure should send the planet back to a technological level equivalent to (probably) the late 1800s in short order, removing the ability to resist the invasion.

Strategic needs might also be the basis for an invasion, but will obviously depend heavily upon the exact circumstances in question, and fall outside the scope of this paper.  All that can be analyzed here is the effect of technological constraints on such strategic requirements.  

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If alien forces are overwhelming but localized, then you don't need to be strong enough to defeat them. You just need to be stronger than your neighbor.

• 

We now know (little consolation though this provides) that the Twerms were fleeing from their hereditary enemies the Mucoids when they first detected Earth on their far-ranging Omphalmoscopes. Thereafter, they reacted with astonishing speed and cunning.

In a few weeks of radio-monitoring, they accumulated billions of words of electroprint from the satellite Newspad services. Miraculous linguists, they swiftly mastered the main terrestrial languages; more than that, they analysed our culture, our technology, our political-economic systems — our defences. Their keen intellects, goaded by desperation, took only months to identify our weak points, and to devise a diabolically effective plan of campaign.

They knew that the US and the USSR possessed between them almost a teraton of warheads. The fifteen other nuclear powers might only muster a few score gigatons, and limited deliver systems, but even this modest contribution could be embarrassing to an invader. It was therefore essential that the assault should be swift, totally unexpected, and absolutely overwhelming. Perhaps they did consider a direct attack on the Pentagon, the Red Fort, the Kremlin, and the other centres of military power. If so, they soon dismissed such naive concepts.

With a subtlety which, after the event, we can now ruefully appreciate, they selected our most compact, and most vulnerable, area of sensitivity ...

Their insultingly minuscule fleet attacked at 4 a.m. European time on a wet Sunday morning. The weapons they employed were the irresistible Psychedelic Ray, the Itching Beam (which turned staid burghers into instant nudists), the dread Diarrhoea Bomb, and the debilitating Tumescent Aerosol Spray. The total human casualties were thirty-six, mostly through exhaustion or heart failure.

• 

Their main force (three ships) attacked Zürich. One vessel each sufficed for Geneva, Basle, and Berne. They also sent what appears to have been a small tugboat to deal with Vaduz.

No armourplate could resist their laser-equipped robots. The scanning cameras they carried in their ventral palps could record a billion bits of information a second. Before breakfast time, they knew the owners of every numbered bank account in Switzerland.

Thereafter, apart from the dispatch of several thousand special delivery letters by first post Monday morning, the conquest of Earth was complete.

• 

(ed note: Miranid of the Farla empire has just finished explaining to Henlo why conventional theory holds that a decisive interstellar war is impossible. Now he explains the sneaky trick they are going to do in order to avoid conventional theory and destroy the upstart barbarian Vilk empire.)

"Our barbarian friends have another weakness, which we have up to this point not been able to utilize without compromising its existence. I 've carefully saved it until now, and they have considerately not discovered it within themselves."

"The Vilks, of course, were able to make war quite successfully. Since they were operating as a horde of mobile independent principalities, and since they were after loot and glory only, they were never forced to gain what civilized nations would term 'victory', or 'conquest.'"

"They were reapers, harvesting the same field again and again, and gradually extending their boarders. They had no time for the re-education of subject peoples to their own ideals or patriotic causes -- a fact further implemented by their total lack of such civilized appurtenances. They merely informed their vassals that they had become the property of whatever Vilk it happened to be, and levied tribute accordingly. They left it to the natural fertility of the Vilk soldier to gradually erase all traces of independent nationality among such nations as could interbreed, and to the natural inertia of generations of slavery among such as could not."

"The result has been the gradual accumulation, in Vilk ranks, of a number of Vilks who are not Vilks."

Miranid seemed anxious to stress the point.

"And these Vilks may be good, barbarian Vilks like all the rest of them. But some of them inevitably feel that their particular kind of Vilk is better fitted to rule the communal roost."

"A situation, you will agree, which does not apply among such civilized communities as Farla, which may have its internal dissensions, but no special uniforms of hide-color, limb-distribution, or digital anomalies around which infra-nationalistic sentiments may be rallied."

Miranid stabbed the chart with his dividers. "We will slice here, here, and here, with most of our lighter units supported by some heavier groups. You and I, Henlo, will take the remainder of the main fleet and spit right through to Vilkai, where we will crown some highly un-Vilkish Vilk king of the Vilks, and then leave him to perish."

"The entire sorry mess will slash itself to suicide in the petty nationalistic squabbles which are sure to follow the precedent we set them. We will be enabled to do so quite easily by the allies which our housewifely intelligence corps have neatly suborned for us."

• 

(ed note: Dr. Calhoun is a member of the interstellar Med service. The service is charged with overseeing the health of the various human colonized worlds. There really isn't anything like an over-arching interstellar government.

Anyway Dr. Calhoun makes a scheduled visit to the planet Maris III. When he arrives, the city is empty, the colonists are in hiding, a strange spaceship is on the landing pad, and a bunch of thugs try to kill him. He eludes them, travels into the country, and makes contact with the colonists. They are all suffering from some genetically engineered plague that is resistant to conventional medicine. The thugs are doing their best to hunt down and kill all the colonists.)

      When he woke, there was a small fire in the glade, about which the exhausted, emaciated fugitives consulted with Calhoun.
     Calhoun was saying bitterly, "The whole thing is wrong! It's self-contradictory, and that means a man, or men, trying to meddle with the way the universe was made to run. Those characters in the city aren't fighting the plague—they're cooperating with it! When I came in a Med Ship, they should have welcomed my help. Instead they tried to kill me so I couldn't perform the function I was made for and trained for! They're going against the way the universe works. From what Helen tells me, they landed with the purpose of helping the plague wipe out everybody else on the planet. They began their butchery immediately. That's why you people ran away."
     The weary, weakened people listened almost numbly.
     "The invaders—and that's what they are," said Calhoun angrily, "have to be immune and know it, or else they wouldn't risk contagion by tracking you down to murder you. The city's infected and they're not alarmed. You're dying and they only try to hasten your death. I arrive, and I might be of use, so they try to kill me. They must know what the plague is and what it does, because their only criticism of it seems to be that it doesn't kill fast enough. And that is out of the ordinary course of nature. It's not intelligent human conduct."
     "A plague's not pleasant, but it's natural. This plague is neither pleasant nor natural. There's human interference with the normal course of events—certainly the way things are going is abnormal. I'm not too sure somebody didn't direct this from the beginning. That's why I shot that man with the crossbow instead of taking a blaster to him. I meant to wound him so I could make him answer questions, but the crossbow's not an accurate weapon and it happened that I killed him instead. There wasn't much information in the stuff in his pockets. The only significant item was a ground-car key, and that only means there's a car waiting for him to come back from hunting you."
     The gaunt young man said drearily, "He didn't come from Dettra, which is our planet. Fashions are different on different worlds, and he wears a uniform we don't have. His clothing uses fasteners we don't use, too. He's from another solar system entirely."

     Calhoun squinted through the glass tube of the filter at the light of the sputtering torch.
     "Almost clumped," he said. Then he added, "I suspect there's been some very fine laboratory work done somewhere to give the invaders their confidence of immunity to this plague. They landed and instantly set to work to mop up the city—to complete the job the plague hadn't quite finished. I suspect there could have been some fine lab work done to make plague mechanism undetectable. I don't like the things I'm forced to suspect!"
     He inspected the glass filter again.
     "Somebody," he said coldly, "considered that my arrival would be an unfavorable circumstance to him and what he wanted to happen. I think it is. He tried to kill me. He didn't. I'm afraid I consider his existence an unfavorable circumstance." He paused, and said very measuredly, "Cooperating with a plague is a highly technical business; it needs as much information as fighting a plague. Cooperation could no more be done from a distance than fighting it. If the invaders had come to fight the plague, they'd have sent their best medical men to help. If they came to assist it, they'd have sent butchers, but they'd also send the very best man they had to make sure that nothing went wrong with the plague itself. The logical man to be field director of the extermination project would be the man who'd worked out the plague himself." He paused again, and said icily, "I'm no judge to pass on anybody's guilt or innocence or fate, but as a Med Service man I've authority to take measures against health hazards!"
     "There's no exact precedent for what's happened here," explained Calhoun. "A thousand years or so ago there was a king of France—a country back on old Earth—who tried to wipe out a disease called leprosy by executing all the people who had it. But lepers were a nuisance. They couldn't work. They had to be fed by charity. They died in inconvenient places and only other lepers dared handled their bodies. They tended to throw normal human life out of kilter. That wasn't the case here. The man I killed wanted you dead for another reason. He and his friends wanted you dead right away."
     The gaunt Kim Walpole said tiredly, "He wanted to dispose of our bodies in a sanitary fashion."
     "Nonsense!" snapped Calhoun. "The city's infected. You lived, ate, breathed, walked in it. Nobody can dare use that city unless they know how the contagion's transmitted, and how to counteract it. Your own colonists turned back. These men wouldn't have landed if they hadn't known they were safe!"
     There was silence.

     "If the plague is an intended crime," added Calhoun, "you are the witnesses to it. You've got to be gotten rid of before colonists from somewhere other than Dettra arrive here."
     The dark-bearded man growled, "Monstrous! Monstrous!"
     "Agreed," said Calhoun. "But there's no interstellar government now, any more than there was a planetary government in the old days back on Earth. So if somebody pirates a colony ready to be occupied, there's no authority able to throw them out. The only recourse would be war. And nobody is going to start an interplanetary war—not with the bombs that can be landed! If the invaders can land a population here, they can keep the place." He paused, and said with irony, "Of course they could be persuaded that they were wrong."
     But that was not even worth thinking about. In the computation of probabilities in human conduct, self-interest is a high-value factor. Children and barbarians have clear ideas of justice due to them, but no idea at all of justice due from them. And though human colonies spread toward the galaxy's rim, there was still a large part of every population which was civilized only in that it could use tools. Most people still remained comfortably barbaric or childish in their emotional lives. It was a fact that had to be considered in Calhoun's profession. It bore remarkably on matters of contagion, and health, and life itself.

     "You'll have to hide. Perhaps permanently," he told them. "It depends partly on what happens to me, however. I have to go to the city. There's a very serious health problem there."
     Kim said with irony, "In the city? Everybody's healthy there. They're so healthy that they come out to hunt us down for sport!"
     "Considering that the city's thoroughly infected, their immunity is a health problem," said Calhoun. "But besides that, it looks like the original cause of the plague is there, too. I'd guess that the originator of this plague is technical director of the exterminating operation that's in progress on this planet. I'd guess he's in the ship that brought the butcher-invaders. I'd be willing to bet that he's got a very fine laboratory on the ship."
     Kim stared at him. He clenched and unclenched his hands.
     "And I'd say it ought to be quite useless to fight this plague before that man and that laboratory were taken care of," said Calhoun. "You people are probably all right. I think you'll wake up feeling better. You may be well. But if the plague is artificial, if it was developed to make a colony planet useless to the world that built it, but healthy for people who want to seize it . . ."
     "What?"
     "It may be the best plague that was developed for the purpose, but you can be sure it's not the only one. Dozens of strains of deadly bugs would have to be developed to be sure of getting the deadliest. Different kinds of concealment would have to be tried, in case somebody guessed the synergy trick, as I did, and could do something about the first plague used. There'd have to be a second and third and fourth plague available. You see?"
     Kim nodded, speechless.
     "A setup like that is a real health hazard," said Calhoun. "As a Med Service man, I have to deal with it. It's much more important than your life or mine or Murgatroyd's. So I have to go into the city to do what can be done. Meanwhile, you'd better lie down now. Give Murgatroyd's antibodies a chance to work. One question, though. If the plague is artificial, it had to be started. Did a ship land here two weeks or a month before your workmen began to be ill? It could have come from anywhere."
     "There was no landing of any ship," said Kim. "No."
     Calhoun frowned. His reasoning seemed airtight. The plague must have been introduced here from somewhere else!
     "There had to be," he insisted. "Any kind of ship! From anywhere!"
     "There wasn't," repeated Kim. "We had no off-planet communication for three months before the plague appeared. There's been no ship here at all except from Dettra, with supplies and workmen and that sort of thing."
     Calhoun scowled. This was impossible. Then Helen's voice sounded very faintly. Kim made a murmurous response. Then he said, "Helen reminds me that there was a queer roll of thunder one night not long before the plague began. She's not sure it means anything, but in the middle of the night, with all the stars shining, thunder rolled back and forth across the sky above the city. This was a week or two before the plague. It waked everybody. Then it rolled away to the horizon and beyond. The weather people had no explanation for it."
     Calhoun considered. Murgatroyd nestled still closer to him. He snapped his fingers suddenly.
     "That was it!" he said savagely. "That's the trick! I haven't all the answers, but I know some very fine questions to ask now. And I think I know where to ask them."
     He settled back. Murgatroyd slept. There was the faintest possible murmur of voices where Kim Walpole and the girl Helen talked wistfully of the possibility of hope.
     Calhoun contemplated the problem before him. There were very, very few survivors of the people who belonged in the city. There was a shipload of murderers—butchers!—who had landed to see that the last of them were destroyed. Undoubtedly there was a highly trained and probably brilliant microbiologist in the invaders' expedition. One would be needed, to make sure of the success of the plague and to verify the absolute protection of the butchers, so that other colonists could come here to take over and use the planet. There could be no failure of protection for the people not of Dettra who expected to inhabit this world. There would have to be completely competent supervision of this almost unthinkable, this monstrous stealing of a world.
     "The plague would probably be a virus pair," muttered Calhoun. "Probably introduced and scattered by a ship with wings and rockets. It'd have wings because it wouldn't want to land, but did want to sweep back and forth over the city. It'd drop frozen pellets of the double virus culture. They'd drop down toward the ground, melting and evaporating as they fell, and they'd flow over the city as an invisible, descending blanket of contagion coating everything. Then the ship would head away over the horizon and out to space on its rockets. Its wings wouldn't matter out of atmosphere and it'd go into overdrive and go back home to wait . . ."
     He felt an icy anger, more savage than any rage could be. With this technique, a confederation of human beings utterly without pity could become parasitic on other worlds. They could take over any world by destroying its people, and no other people could make any effective protest, because the stolen world would be useless except to the murderers who had taken it over. This affair on Maris III might be merely a test of the new ruthlessness. The murderer planet could spread its ghastly culture like a cancer through the galaxy.
     But there were two other things involved beside a practice of conquest through murder by artificial plagues. One was what would happen to the people—the ordinary, commonplace citizens—of a civilization which spread and subsisted by such means. It would not be good for them. In the aggregate, they'd be worse off than the people who died.
     The other?
     "They might make a field test of their system," said Calhoun very coldly, "without doing anything more serious to the Med Service than killing one man—me—and destroying one small Med Ship. But they couldn't adopt this system on any sort of scale without destroying the Med Service first. I'm beginning to dislike this business excessively!"

---

(ed note: Calhoun manages to infiltrate the invader's ship and captures Doctor Death. Who predictably is a physically deformed sociopath who won't be happy until he makes the universe pay for all the abuse he was subjected to. From the chair he is tied to, Doctor Death tries to bribe Calhoun with visions of ruling entire planets)

     It was quite horrible.
     His captive went on. His tone wheedled, and was strident, and in turn was utterly convincing and remarkably persuasive.
     Once Maris III was occupied by colonists from the world that had sent the plague, nothing could be done. Dettra Two could never land its people in the city. They would die. Only the usurping population could survive there. For all time to come the world of Maris III must belong to the folk who had planted it with death. The permanent colonists here must be immunized like the members of the invading party themselves.
     "Who," said Calhoun, "are not as happy as they used to be."
     His captive licked his lips and went on, his eyes deadly and his tone reasonable and seductive and remarkably hypnotic.
     But Maris III was only a test. Once the process was proved here, there were other worlds to be taken over. Not only new colony-worlds like this. Old and established worlds would find themselves attacked by plagues their doctors would be helpless to combat. Then there would come ships from the world that had tried out its technique on Maris III. The ships would end the plagues. They would prove it. They would offer to sell life to all the citizens of the dying worlds—at a price.
     "Unprofessional," said Calhoun, "but probably profitable."
     The price, in effect, would be submission. It would amount to slavery. Those who would not accept the bargain would die.
     "Of course," said Calhoun, "they might try to back out of such a bargain later."
     His captive smiled a thin-lipped smile, while his eyes did not change at all. He explained convincingly that if there was a revolt, it would not matter. The countermeasure to a new defiance would always be a new plague. There were many plagues ready to use. They would build an interstellar empire in which rebellion would be a form of suicide. No world once taken over could ever free itself. No world once chosen could possibly resist. There would be worlds by tens and scores and hundreds to be ruled by men like Calhoun. He would rate a planet-kingdom of his own. His Med Service training entitled him to an empire! He would be absolute ruler and absolute master of millions of abject slaves who must please his most trivial whim or die!
     "An objection," said Calhoun. "You haven't mentioned the Med Service. I don't think it would take kindly to such a system of planetary conquest."
     Here was the highest test of the prisoner's ability to sway and persuade and convince and almost to hypnotize. He had a matter of minutes to make the Med Service ridiculous, and to point out the defenselessness of its Sector Headquarters, and then—without arousing ancient prejudices—to make it seem natural and inevitable and almost humorous that Med Service Sector Headquarters would receive special precautionary fusion-bomb treatment as soon as the Maris III task was finished. Calhoun stirred. His prisoner spoke even more urgently, more desperately. He pictured worlds on which every living being would be Calhoun's slave—
     "That'll do," said Calhoun. "I've got the information I wanted."
     "Then release me," said his prisoner eagerly. And then his burning eyes read Calhoun's no-longer-guarded expression.
     "You accept," he cried fiercely. "You accept! You can't refuse! You can't!" 
     "Of course I can," said Calhoun annoyedly. "You've no idea! I wouldn't want a million slaves, or even one. I'm reasonably sane! And such a crazy scheme couldn't work anyhow. Sheer probability would throw in so many unfavorable chance happenings that it would be bound to go smash. I'm proof of it. I'm an unfavorable chance happening right here, the very first time you tried the beastly business."

---

     "The first load of immunized, enthusiastic colonists are in orbit now, giving the gang aground a little more time to answer. I want you people to talk to them."
     "We'll bring their ship down," said the broad-bearded man hungrily, "and blast them as they come out of the port!"
     Calhoun shook his head.
     "To the contrary," he said mildly. "You'll put on the clothes of some of our prisoners, and you'll let yourselves be seen by the joyous newcomers in their spacephone screen. You'll pretend to be the characters we really have safely sleeping, and you'll say that the plague worked much too well. You'll say it wiped out the original inhabitants—that's you—and then changed into a dozen other plagues and wiped out all the little butcher-boys who came to mop up. You'll give details of the other kinds of plague that the real plague turned into. You'll be pathetic. You'll beg them to land and pick up you four or five dying, multiply diseased, highly contagious survivors. You'll tell them the plague has mutated until even the native animals are dying of it. Flying things fall dead from the air. Chirping things in the trees and grass are wiped out. You'll picture Maris III as a world on which no animal life can hope ever to live again—and you'll beg them to come down and pick you up and take you home with them."
     The broad-bearded man stared. Then he said, "But they won't land."
     "No," agreed Calhoun. "They won't. They'll go home. Unless the government has them all killed before they can talk, they'll tell their world what happened. They'll be half-dead with fear that the immunizing shots they received will mutate and turn them into the kind of plague victims you'll make yourself look like. And just what do you think will happen on the world they came from?"
     Kim said hungrily, "They'll kill their rulers. They'll try to do it before they die of the plagues they'll imagine. They'll revolt! If a man has a belly-ache he'll go crazy with terror and try to kill a government official because his government has murdered him!"
     Kim drew a deep breath. He smiled with no amusement at all.
     "I like that," he said with a sort of deadly calm. "I like that very much."
     "After all," observed Calhoun, "once an empire had been started, with the subjugated populations kept subdued by a threat of plague, how long would it be before the original population was enslaved by the same threat? Go and invent some interesting plagues and make yourselves look terrifying. Heaven knows you're lean enough! But you can make yourselves look worse. I said, once, that a medical man sometimes has to use psychology in addition to the regular measures against plague. The Med Service will check on that planet presently, but I think its ambition to be a health hazard to the rest of the galaxy will be ended."
     So they did. It was odd how they could take a sort of pleasure in the enactment of imagined disaster even greater than they had suffered. Their eyes gleamed happily as they went about their task.

     The passenger ship went away. It did not have a pleasant journey. When it landed, its passengers burst tumultuously out of the spaceport to tell their story. Their home world went into a panic which was the more uncontrollable because the people had been very carefully told how deadly the tamed plagues would be to the inhabitants of worlds that they might want to take over. But now they believed the tamed plagues had turned upon them.
     The deaths, especially among members of the ruling class, were approximately equal in number to those a deadly pandemic would have caused.

(ed note: the aliens are trying to invade Terra, and quickly discover that they've poked a hornet's nest. So they try using bio-weapons. Which just make the Terrans more angry. The aliens send a over-General who asks the invasion commander what the heck went wrong?)

      "Well, what could we do? We'd planned a neat surgical strike with minimum losses. Instead, the locals went berserk. There was no way we could hope to militarily fight it out on their terms—they had the whole resources of the planet at hand, and we only had what was with us.The obvious thing was to use our scientific superiority to hamstring them."
     "Specifically?"
     "We set up bioduplication bases, got out our stock of tailored pests, found out which ones seemed to fit, dropped around twenty thousand flights of sixteen-legged jangerls, stingbats, and burrowing trap-adders to poison and terrorize the natives, and give them a little warning that they'd better cooperate."

     "How did that work?"
     "Well, till we used the pests, there was tough resistance. After that, it got vicious. These split-up groups (the nations of Terra) formed an alliance, got this native here (the Terran genius tactician), in front of us, to run things overall, and he got them actively working together. Before long, their measures and their counterblows were on a level we hadn't even imagined was possible. They even adopted a simplified common language to be able to hit us harder. Everything got worse after we started using pests. But what else could we do?"

     "Be specific. What incident led you to call for help?"
     "Well, we'd just landed two or three million forty-legged flatstings genetically engineered to kill natives, and the natives had come out with a dust that killed flatstings, and then they fired a swarm of missiles that came up off the planet and shot out into space. Only a few came anywhere near us, so we figured their control was breaking down. That was when I sent that report that we were getting the edge on them. Well, these missiles kept coming up, but we were happy to see them waste their firepower, figured we'd won, and called on them to surrender. About then, a missile streaked in from nowhere and hit us from behind. The next thing you knew, they were coming in from all directions, and we realized all these seemingly wasted missiles had been set to come back at us. There was no possible way we could defend against this.
     "These things blew up the Moon Command Base, the bio-teams, the germ-synthesis labs, Tactical Combat Center, and Fleet Refit Base, and all that survived were our forces actually on the planet, and our ships in transit.

• 

Even if star travel is impossible; "mere" communications could do a lot of damage. After all, this is the basis on which all censors act. A really malevolent (interstellar) society could destroy another one quite effectively by a few items of well-chosen information (sent by radio). ("Now, kiddies, after you’ve prepared your uranium hexafluoride…")

---

Fred Hoyle has expressed the view that there may be a kind of Galactic communications network, linking thousands or millions of worlds. Within a very few centuries, we may be clever enough to plug ourselves into the circuit; it may take us a little longer to understand what the other subscribers are saying.

The possibilities opened up even by one-way communication (passive eavesdropping) are almost unlimited. The signals would certainly contain visual material—not necessarily real-time TV—which it would be rather easy to reconstruct. And then, across the light-years, we would be able to look at other worlds and other races…

The things we could learn might change our own society beyond recognition. It would be as if the America of Lincoln’s time could tune into the TV programs of today; though there would be much that could not be understood, there would also be clues that could leapfrog whole technologies into the future. (Ironically enough, the commercials would contain some of the most valuable information!) Nineteenth-century views would see that heavier-than-air machines were possible, and simple observation would reveal the principles of their design. The still unimagined uses of electricity would be demonstrated (the telephone, the electric light…), and this would be enough to set scientists on the right track. For knowing that a thing can be done is more than half the battle.

As signals from the stars could be received only by nations possessing very large radio telescopes, there would be the opportunity—and the temptation—to keep them secret. Knowledge is the most precious of all commodities, and it is a strange thought that the balance of power may one day be shifted by a few micromicrowatts collected from the depths of space. Yet it should no longer surprise us; for who dreamed, fifty years ago, that the faint flicker of dying atoms in a physics lab would change the course of history?

Glimpses of supercivilizations could have either stimulating or stultifying effects on our society. If the technological gulf was not too great to be bridged, and the programs we intercepted contained hints and clues that we could understand, we would probably rise to the challenge. But if we found ourselves in the position of Neanderthalers confronted by New York City, the psychological shock could be so great that we might give up the struggle. This appears to have happened on our own world from time to time, when primitive races have come into contact with more advanced ones. We will have a good chance of studying this phenomenon in a very few years, when communications satellites start beaming our TV programs into such places as the Amazon jungle. This is the last century during which widely disparate cultures will exist on Earth; would-be students of astrosociology should make the most of their opportunity before it vanishes forever. And no one will be surprised to hear that Margaret Mead is intensely interested in space flight…

• 

      While it has been argued that sustainable ETI is un-likely to be harmful (Baum et al. 2011), we can not exclude this possibility. After all, it is cheaper for ETI to send a malicious message to eradicate humans compared to sending battleships.
     If ETI exist, there will be a plurality of good and bad civilizations. Perhaps there are few bad ETI, but we cannot know for sure the intentions of the senders of a message. Consequently, there have been calls that SETI signals need to be “decontaminated” (Carrigan 2004, 2006).
     In this paper, we show that it is impossible to decontaminate a message with certainty. Instead, complex messages would need to be destroyed after reception in the risk averse case.
     If such a message is received only in one place, and only once, it might be possible to contain it and its harmful consequences, or even destroy it. If it is received repeatedly, perhaps even by amateurs, containment is impossible. As a further complication, the International Academy of Astronautics has adopted a “Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence” which states1 that “These recordings should be made available to the international institutions listed above and to members of the scientific community for further objective analysis and interpretation.” This view is shared by the majority of SETI scientists (Gertz 2017).

3. THE NEED FOR A PRISON

     We continue with a hypothetical message which appears to be, at first sight, positive and interesting, and shall be analyzed in depth. Any message could, in principle, be examined on paper. For many plausible message types, however, it is much more convenient to use a computer. Even the simple LATEX notation is difficult to read as code. Consider the proof of the Riemann hypothesis, which begins with the equation

\zeta(s)=\sum_{n=1}^{\infty}\frac{1}{n^s}=\prod_{p\\text{prim}}\frac{1}{1\frac1{p^s}}=\frac1{\left(1-\frac1{2^s}\right)\left(1-\frac1{3^s}\right)\left(1-\frac1{5^s}\right)\dotsm}

     which is much easier to read when interpreted and finely printed as

• 

     Even a typesetting system such as TEX is a Turing-complete programming language (Greene 1990), so that the message is in fact code, and may contain a malicious virus. Messages may contain large technical diagrams, equations, algorithms etc. which can not reasonably be printed and examined manually. In addition, the message itself might be compressed to increase interstellar data rates, and the decompression algorithm would be code. Executing billions of decompression instructions cannot plausibly be performed manually and requires the use of a computer. But then, the computer would execute potentially harmful ETI code. For this case, it was suggested to use isolated, quarantined machines for analysis (Carrigan 2004, 2006).
     In the following section, we explain why these measures are insufficient, and no safety procedure exists to contain all threats.

4. THERE IS NO PERFECT PRISON

     Consider a large ETI message with a header that contains a statement such as “We are friends. The galactic library is attached. It is in the form of an artificial intelligence (AI) which quickly learns your language and will answer your questions. You may execute the code following these instructions...”
     We assume that the message is available only to a small group of people, part of a government body, who decide to keep it private, but follow their curiosity and examine it with utmost care. A computer in a box on the moon is built to execute the code. Safety devices are in place, their design by choice of the reader, such as remote-controlled fusion bombs to terminate the experiment at any time.
     This scenario resembles the Oracle-AI, or AI box, of an isolated computer system where a possibly dangerous AI is “imprisoned” with only minimalist communication channels. Current research indicates that even well-designed boxes are useless, and a sufficiently intelligent AI will be able to persuade or trick its human keepers into releasing it (Armstrong et al. 2012; Dawson et al. 2016).
     For the escape, we have to assume that researchers engage in a conversion with the AI (without, there would be no benefit in running the experiment in the first place). In such a text conversion, the AI might offer things of value, such as a cure for cancer, and make a small request in exchange, such as a 10% increase in its computer capacity. It appears rational to take the offer. When we do, we have begun business and trade with it, which has no clear limit. If the cure for cancer would consist of blueprints for nanobots: should we build these, and release them into the world, in the case that we don’t understand how they work? We could decline such offers, but shall not forget that humans are involved in this experiment. Consider a nightly conversation between the AI and a guard: “Your daughter is dying from cancer. I give you the cure for the small price of...”. We can never exclude human error and emotions. After all, is it ethical to keep a sentience in a prison when it expresses incredible pain due to small manufacturing errors from building the box?
     Even in a military-style, adamant experiment, there will still be humans involved who go home after examination work with their own feelings. Even if everything is officially secret, whistle-blowers might get some news out to the public. Quickly, there could be a community on Earth in favor of letting it out for religious, philosophical etc. reasons. If the AI promises to cure cancer, or offers a message of salvation, a cult could form. Maybe (or maybe not) a majority of the population would be in favor of releasing the AI. Should, or even could, a democratic government work against the majority of its people? Dictatorships are unstable and eventually over-thrown; the AI will be eventually released.

5. PRISON ESCAPE

     With a non-zero prison escape probability in any single time period, the AI will be free at some point of time. Then, the worst possible result would be human extinction or some other unrecoverable global catastrophe (Bostrom 2014). The main argument is that the human species currently dominates planet Earth because of our intelligence. If ETI-AI is superior, it might (or might not) become more powerful and consider us as irrelevant monkeys (or maybe not).

• 

(ed note: In the story, SETI scientist make radio contact with the alien inhabitants of Mu Cassiopeiae, a spectral class G5Vb star about 25 light-years away. Sadly the scientist cannot get any scientific information from the aliens since the entire planet is under a religious dictatorship. They receive nothing except the alien equivalent of evangelical proselytizing pamphlets. Kind of like an interstellar version of The Watchtower.)

“ ‘—begat Manod, who reigned over the People for 99 years. And in his day lawlessness went abroad in the land, wherefore the Quaternary One smote the People with ordseem (Apparently a disease—Tr.) and they were sore afflicted. And the preacher Jilbmish called a great prayer meeting. And when the People were assembled he cried unto them: Woe betide you, for you have transgressed against the righteous command of the Secondary and Tertiary Ones, namely, you have begrudged the Sacrifice and you have failed to beat drums (? —Tr.) at the rising of Nomo, even as your fathers were commanded; wherefore this evil is come upon you.’ Sheemish xiv, 6.

“Brethren beyond the stars, let us ponder this text together. For well you know from our previous messages that ignorance of the Way, even in its least detail, is not an excuse in the sight of the Ones. 'Carry Our Way unto the ends of creation, that ye may save from the Eternal Hunger all created beings doomed by their own unwittingness.’ Chubu iv, 2. Now the most elementary exegesis of the words of Jilbmish clearly demonstrated—

Father James Moriarty, S.J., sighed and laid down the typescript. Undoubtedly the project team of linguists, cryptographers, anthropologists, theologians and radio engineers was producing translations as accurate as anyone would ever be able to.

Father Moriarty had been assured that the different English styles corresponded to a demonstrable variation in the original language. So he accepted the edited translation of the messages from Mu Cassiopeiae. “Only why,” he asked himself as he stuffed his pipe, “must they use that horrible dialect?” He touched a lighter to the charred bowl and added, “Pseudo-King James,” with a bare touch of friendly malice.

---

“And the biology, biochemistry, zoology, botany, anthropology, history, sociology … and who knows how far ahead of us they may be in some technologies? Sure. Those hopes were expressed before I was born,” snapped Strand. “But what have we actually learned so far? One language. A few details of dress and appearance. An occasional datum of physical science, like that geological information you spoke of. In more than a hundred years, that’s all!”

---

“Religious ranting, you mean,” said Strand sourly.

Moriarty grimaced. “Correct word, that. I was reading the latest translation you’ve released, on my way here. No sign of any improvement, is there?”

"Nope,” Okamura said. "As of twenty-five years ago, at least, Akron’s still governed by a fanatical theocracy out to convert the universe.” He sighed. "I imagine you know the history of Ozma’s contact with them? For the first seventy-five years or so, everything went smoothly. Slow and unspectacular, so that the public got bored with the whole idea, but progress was being made in understanding their language. And then—when they figured we’d learned it well enough—they started sending doctrine. Nothing but doctrine, ever since. Every message of theirs a sermon, or a text from one of their holy books followed by an analysis that my Jewish friends tell me makes the medieval rabbis look like romantic poets. Oh, once in a great while somebody slips in a few scientific data, like that geological stuff which got you so interested. I imagine their scientists are just as sick at the wasted opportunity as ours are. But with a bunch of Cotton Mathers in control, what can they do?”

‘Tes, I know all that,” said Moriarty. "It’s a grim sort of religion. I daresay anyone who opposes its ministers is in danger of burning at the stake, or whatever the Akronite equivalent may be.”

Okamura seemed so used to acting as dragoman for visitors who cared little and knew less about Ozma, that he reeled off another string of facts the priest already had by heart. “Communication has always been tough. After the project founders first detected the signals, fifty years must pass between our acknowledgment and their reply to that. Of course, they’d arranged it well. Their initial message ran three continuous months before repeating itself. In three months one can transmit a lot of information; one can go all the way from ‘two plus two equals four’ to basic symbology and telling what band a sonic ‘cast will be sent on if there’s an answer. Earth’s own transmission could be equally long and carefully thought out. Still, it was slow. You can’t exactly have a conversation across twenty-five light-years. All you can do is become aware of each other’s existence and then start transmitting more or less continuously, meanwhile interpreting the other fellow’s own steady flow of graded data. But if it weren’t for those damned fanatics, we’d know a lot more by now than we do.

“As it is, we can only infer a few things. The theocracy must be planet-wide. Otherwise we’d be getting different messages from some other country on Akron. If they have interstellar radio equipment, they must also have weapons by which an ideological dictatorship could establish itself over a whole world, as Communism nearly did here in the last century. The structure of the language, as well as various other hints, proves the Akronites are mentally quite humanlike, however odd they look physically. We just had the bad luck to contact them at the exact point in their history when they were governed by this crusading religion.”

---

The next word in the sentence from Aejae xliii, 3 which we are considering is ‘mchiruchin,’ an archaic word concerning whose meaning there was formerly some dispute. Fortunately, the advocates of the erroneous theory that it means ‘very similar’ have now been exterminated and the glorious truth that it means ‘quite similar’ is firmly established.”

---

     Strand leaned back in his swivel chair. His glum hostility was dissolving into bewilderment. “What’re you getting at? Look here, uh, Father, it’s physically impossible for us to change the situation on Akron—"
     "Oh?”
     “What d’ you mean?”
     “We can send a reply to those sermons.”
     “What?” Strand almost went over backward.
     “Other than scientific data, I mean. I assure you. Dr. Strand, all I want is a free scientific and cultural exchange with Mu Cassiopeiae.”
     The director reseated himself, leaned elbows on desk and stared at the priest. He wet his lips before saying: “What do you think we should do, then?”

“Why, break up their theocracy. What else? There’s no sin in that! My ecclesiastical superiors have approved my undertaking. They agree with me that the Akronist faith is so unreasonable it must be false, even for Akron.

“Maybe I got you wrong,” he said grudgingly. “But, uh, how do you propose to do this? Wouldn’t you have to try converting them to some other belief?”

“Impossible,” said Moriarty. “Let’s suppose we did transmit our Bible, the Summa, and a few similar books. The theocracy would suppress them at once, and probably cut off all contact with us.”

He grinned. “However,” he said, "in both the good and the bad senses of the word, casuistry is considered a Jesuit specialty.” He pulled the typescript he had been reading from his coat pocket. “I haven’t had a chance to study this latest document as carefully as I have the earlier ones, but it follows the typical pattern. For example, one is required ‘to beat drums at the rising of Nomo,’ which I gather is the third planet of the Ohio System. Since we don’t have any Nomo, being in fact the third planet of our system it might offhand seem as if , we’re damned. But the theocracy doesn’t believe that, or it wouldn’t bother with us. Instead, their theologians, studying the astronomical data we sent, have used pages and pages of hairsplitting logic to decide that for us Nomo is equivalent to Mars.”

“What of it?” asked Strand; but his eyes were kindling.

“Certain questions occur to me,” said Moriarty. “If I went up in a gravicar, I would see Mars rise sooner than would a person on the ground. None of the preachings we’ve received has explained which rising is to be considered official at a given longitude. A particularly devout worshipper nowadays could put an artificial satellite in such an orbit that Mars was always on its horizon. Then he could beat drums continuously, his whole life long. Would this gain him extra merit or would it not?”

“I don’t see where that matters,” said Strand.

“In itself, hardly. But it raises the whole question of the relative importance of ritual and faith. Which in turn leads to the question of faith versus works, one of the basic issues of the Reformation. As far as that goes, the schism between Catholic and Orthodox Churches in the early Middle Ages turned, in the last analysis, on one word in the Credo, filioque. Does the Holy Ghost proceed from the Father and the Son, or from the Father alone? You may think this is a trivial question, but to a person who really believes his religion it is not. Oceans of blood have been spilled because of that one word.

“Ah…returning to this sermon, though. I also wonder about the name ‘Nomo.’ The Akronite theologians conclude that in our case, Nomo means Mars. But this is based on the assumption that, by analogy with their own system, the next planet outward is meant. An assumption for which I can recall no justification in any of the scriptures they’ve sent us. Could it not be the next planet inward—Venus for us? But then their own ‘Nomo’ might originally have been Mu Cassiopeiae I, instead of III. In which case they’ve been damning themselves for centuries by celebrating the rising of the wrong planet!”

Strand pulled his jaw back up. “I take it, then,” he said huskily, “you want to—”

“To send them some arguments much more elaborately reasoned than these examples, which I’ve simply made up on the spot,” Moriarty answered. “I’ve studied the Akronist faith in detail… with two millennia of Christian disputation and haggling to guide me. I’ve prepared a little reply. It starts out fulsomely, thanking them for showing us the light and begging for further information on certain points which seem a trifle obscure. The rest of the message consists of quibbles, puzzles, and basic issues.”

“And you really think— How long would this take to transmit?”

“Oh, I should imagine about one continuous month. Then from time to time, as they occur to us, we can send further inquiries.”

Epilogue

(ed note: about 75 years later)

“Time sure passes. But I had to call you right away, Jim. Transmission from Akron resumed three hours ago.”

“What?” Moriarty glanced at the sky "What’s their news?”

“Plenty. They explained that the reason we haven’t received anything from them for a decade was that their equipment got wrecked in some of the fighting. But now things have quieted down. All those conflicting sects have been forced to reach a modus vivendi.

Apparently the suggestions we sent, incidental to our first disruptive questions seventy-five years ago—and based on our own experience— were helpful: separation of church and state, and so on. Now the scientists are free to communicate with us, uncontrolled by anyone else. They’re sure happy about that! The transition was painful, but three hundred years of stagnation on Akron have ended. They’ve got a huge backlog of data to give us. So if you want your geology straight off the tapes, you better hurry here. All the journals are going to be snowed under with our reports.”

• 

• 

Memeweave: Threats and Other Dangers/Perversion Watch/Open Access
Classification: WHITE (General Access)
Encryption: None
Distribution: Everywhere (Bulk)
As received at: SystemArchiveHub-00 at Víëlle (Imperial Core)
Language: Eldraeic->Universal Syntax
From: 197th Perversion Response Board

Gentlesophs,

Given the high levels of uninformed critical response to our advisory concerning handling potential refugees arriving sublight from regions within the existential threat zone of the Siofra Perversion, or Leviathan Consciousness as it is becoming popularly known, the Board now provides the following explication.

The present situation is an example of what eschatologists refer to as the basilisk-in-a-box problem. The nature of the mythological basilisk is that witnessing its gaze causes one to turn to stone, and the challenge therefore to determine if there is a basilisk within the box and what it is doing without suffering its gaze. The parallel to the Siofra Perversion’s communication-based merkwelt should be obvious: it won’t subsume you unless you alert it to your existence as “optimizable networked processing hardware” by communicating with it.

Your analogous challenge, therefore, is to determine whether the hypothetical lugger or slowship filled with refugees is in fact that, or is contaminated/a perversion expansion probe, without communicating with it – since if it is the latter and you communicate with it sufficiently to establish identity, you have just arranged your own subsumption – and unless people are subsequently rather more careful in re communicating with you, that of all locally networked systems and sophonts.

Currently, the best available method for doing this is based on the minimum-size thesis: i.e., that basilisk hacks, thought-viruses, and other forms of malware have a certain inherent complexity and as such there is a lower limit on the number of bits necessary to represent them. However, it should be emphasized that this limit is not computable (as this task requires a general constructive solution to the Halting Problem), although we have sound reason to believe that a single bit is safe.

This method, therefore, calls for the insertion of a diagnostician equipped with the best available fail-deadly protections and a single-bit isolated communications channel (i.e., tanglebit) into the hypothetical target, there to determine whether or not perversion is present therein, and to report a true/false result via the single-bit channel.

If we leave aside for the moment that:

(a) there is a practical difficulty of performing such an insertion far enough outside inhabited space as to avoid all possibility of overlooked automatic communications integration in the richly meshed network environment of an inhabited star system, without the use of clipper-class hardware on station that does not generally exist; and

(b) this method still gambles with the perversion having no means, whether ontotechnological or based in new physics, to accelerate its clock speed to a point which would allow it to bypass the fail-deadly protections and seize control of the single-bit channel before deadly failure completes.

The primary difficulty here is that each investigation requires not only a fully-trained forensic eschatologist, but one who is both:

(a) a Cilmínár professional, or worthy of equivalent fiduciary trust, and therefore unable to betray their clients’ interests even in the face of existential terror; and

(b) willing to deliberately hazard submitting a copy of themselves into a perversion, which is to say, for a subjective eternity of runtime at the mercy of an insane god.

(Regarding the latter, it may be useful at this time to review the ethical calculus of infinities and asymptotic infinities; we recommend On the Nonjustifiability of Hells: Infinite Punishments for Finite Crimes, Samiv Leiraval-ith-Liuvial, Imperial University of Calmiríë Press. Specifically, one should consider the mirror argument that there is no finite good, including the preservation of an arbitrarily large set of mind-states, which justifies its purchase at infinite price to the purchaser.)

Observe that a failure at any point in this process results in first you, and then your entire local civilization, having its brains eaten.

We are not monsters; we welcome any genuine innovation in this field which would permit the rescue of any unfortunate sophonts caught up in scenarios such as this. However, it is necessary that the safety of civilization and the preservation of those minds known to be intact and at hazard be our first priority.

As such, we trust these facts adequately explain our advisory recommendation that any sublight vessels emerging from the existential threat zone be destroyed at range by relativistic missile systems.

For the Board,

Gém Quandry, Eschatologist Excellence

• 

      One night, during their absence, and close to the front door, something grew. The scientists, after long conference, decided it was a plant but it didn't look like a plant.
     It was a triangular mirror balanced on a cable-like stem as thick as a man's wrist. The "mirror" followed the sun and, at evening or on dull days, folded itself up geometrically into a neat square black box.
     Two days later there was another growth. This was a small brass colored sphere about the size of a walnut perched on the top of a thin black rod about two feet in height.
     An intrigued expert touched it with his hand and was flung untidily to the path. He was not dead but the local hospital had some difficulty bringing him round. A diagnostician pronounced near-lethal electric shock.

---

     The door of Lipscombe's house had been open and on the path was—It had looked like an oxygen cylinder some six feet in length and supported itself on thin legs like black cables. On top, near the thicker end, something spun rapidly, catching the sunlight. He'd had the curious impression that something was watching through it and the thought radar vision had occurred to him before the soldiers had bustled him out of the room.

---

     After much security checking they were finally admitted to a pleasantly furnished recreation room where a group of obvious scientists were arguing fiercely.
     "But, my dear fellow, why should such a conclusion strike you as pure fantasy?"
     "Because the conception in itself is preposterous—the term natural electronic life is a sheer absurdity."
     "Why should it be? When one considers the incredible complication of normal organic life why should not a simpler, less complex life form evolve in a different environment. A planet with a highly radio-active crust, a chemical atmosphere and, possibly, rich surface metal deposits and you have the perfect incubator for electronic life to develop. Consider, an almost pure copper deposit, a few drops of acid from the chemical atmosphere, a natural vein of metallic ore and you have not only natural electricity, but the basis for a natural circuit, or, if you prefer it, an electronic nervous system. Have you read what Mayer deduced during his experiments with radio-active crystals, for example?"
     "I have, but the fact that these artificial cells developed apparent reflexes is no basis for presupposing the preposterous."
     "My God, man, you conceded yesterday that we can make organic life cells in a laboratory. You must also concede, therefore, that this same organic life has evolved naturally on this planet. Why, then, knowing also that electrical life has also been constructed in a laboratory will you not admit the possibility of electronic life evolving naturally?"
     "I still find the conception of intelligent life housed in a metallic body and based on series of circuits wildly improbable. The theory of outworld invasion by what you call an electronic life form is, in my opinion, sheer imagination and owes nothing whatever to applied science."

---

     "What good do they think all these troops and weapon experts will do? They're still thinking in terms of an outworld alien invader with super weapons and they're not. Why the hell can't they see that? This is a minor occupation force sitting on its presumed backside in one of the safest conquests it's possible to conceive. They've introduced their own ecology into this environment and, because it's dominant in respect of our own, we're going under. Oh yes, I know it looks horrible and alien to our own but the principle is the same. We have sparrows and they introduce hawks. We have oak trees but along comes a strangling ivy; it's as simple as that. Some of the alleged machines our troops are now reporting may be equivalent of wolves or tigers and not armored vehicles at all. Once or twice they have opened up with something new, but this, I think, is reflex. At times we may be an irritant and the aliens take a smack at us like a dozing man slapping at a fly. They can afford to doze, chuck a few seeds out of the window, let loose some hawks and nature will do the job for them. Not too far in the future they can step out of the front door into world which is seeded, prepared and ready for them. Their peculiar ecology will have removed anything alien which might once have cluttered up the place."

• 

     He heard Miramon draw in his breath slightly to answer, but he was never to know what that answer would have been; for at the same moment, Miramon’s whole board came alive at once.
     “Hey!” Amalfi squalled. “Wait for orders down there, dammit!”
     “STANDING ORDERS, MR. MAYOR. AFTER COUNTDOWN BEGINS WE ARE TO ACT AT THE FIRST SIGN OF OUTSIDE INTERFERENCE. COUNTDOWN BEGAN TWELVE HUNDRED SECONDS AGO, AND SEVEN SECONDS AGO OUTSIDE INTERFERENCE BECAME STATISTICALLY SIGNIFICANT.”
     “What do they mean?” Miramon said, trying to read every instrument on his board at once. “I thought I understood your language, Mayor Amalfi, but—”
     “The City Fathers don’t speak Okie, they speak Machine,” Amalfi said grimly. “What they mean is that the Web of Hercules—if that’s who it is—is coming in on us. And coming in on us fast.”
     With a single, circumscribed flip of his closed fingers, Miramon turned off the lights.
     Blackness. Then, seeping faintly over the windows around the tower, the air-glow of the zodiacal light; then, still later, the dim pinwheels of island universes. On Miramon’s board, there was a single spearpoint of yellow-orange which was only the heater of a vacuum tube smaller than an acorn; in this central gloom at the heart and birthplace of the universe, it was almost blinding. Amalfi had to turn his back on it to maintain the profound dark-adaptation that his vision needed to operate at all in the tower on his mountain.
     While he waited for his sight to come back, he wondered at the speed of Miramon’s reaction, and the motives behind it. Surely the Hevian could not believe that a set of pilot lights in a tower on top of a remote mountain could be bright enough to be seen from space; for that matter, blacking out even as large an object as a whole planet could serve no military purpose—it had been two millennia since any reasonably sophisticated enemy depended upon light alone to§see by. And where in Miramon’s whole lifetime could he have acquired the blackout reflex? It made no sense; yet Miramon had restored the blackout with all the trained positiveness of a boxer riding with a punch.
     When the light began to grow, he had his answer—and no time left to wonder how Miramon had anticipated it.
     It began as though the destruction of the inter-universal messenger were about to repeat itself in reverse, encompassing the whole of creation in the process. Crawls of greenish-yellow light were beginning to move high up in the Hevian sky, at first as ghostly as auroral traces, then with a purposeful writhing and brightening which seemed as horrifyingly like life as the copulation of a mass of green-gold nematode worms seen under phase-contrast lighting. Particle counters began to chatter on the board, and Hazleton jumped to monitor the cumulative readings.
     “Where is that stuff coming from—can you tell?” Amalfi said.
     “It seems to come from nearly a hundred discrete point-sources, surrounding us in a sphere with a diameter of about a light year,” Miramon said. He sounded preoccupied; he was doing something with controls whose purpose was unknown to Amalfi.
     “Hmm. Ships, without a doubt. Well, now we know where they get their name, anyhow. But what is it they’re using?”
     “That’s easy,” Hazleton said grimly. “It’s antimatter.”
     “How can that be?”
     “Look at the frequency analysis on this secondary radiation we’re getting, and you’ll see. Every one of those ships must be primarily a particle accelerator of prodigious size. They’re sending streams of stripped heavy antimatter atoms right down the gravitational ingeodesics toward us—that’s what makes the paths the stuff is following look so twisted. They’ve found a way to generate and project primary cosmics made of antimatter atoms, and in quantity. When they strike our atmosphere, both disintegrate—”
     “And the planet gets a dose of high-energy gamma radiation,” Amalfi said. “And they must have known how to do it for a long time, since they’re named after the technique. Helleshin! What a way to conquer a planet! They can either sterilize the populace, or kill it off, at will, without ever even coming close to the place.”
     “We’ve had the sterility dose already,” Hazleton said quietly.
     “That can hardly matter now,” Estelle said, in an even softer voice.
     “The killing dose won’t matter either,” Hazleton said, “Radiation sickness takes months to develop, even when it’s going to be fatal.”
     “They could disable us quickly enough,” Amalfi said harshly. “We’ve got to stop this somehow. We need these last days!”