This section is for attacking a planet from orbit. The next section is for defending a planet from orbit.
After all the interplanetary battles are over, and the defender's space fleets have been reduced to ionized plasma or fled in panic, the pendultimate stage is entered. The defenders orbital and planetary fortresses have to be neutralized, or at least neutralized enough so that ground troops can be inserted to set up a beachhead.
But please understand that bombing a planet back into the stone age is something that makes more sense in simplistic space operas, not in realpolitik.
Ken does have a good point. The motivation of the invaders puts limits on the allowed invasion techniques. If the invaders want slaves, it is counterproductive to kill every living thing on the defending planet. If the invaders want real estate, it is counterproductive to dust the planet with enough radioactive material to render it uninhabitable for the next ten thousand years. And so on.
The lack of a logical reason for invasion is up to the author to devise a solution for. Some of the motivational questions can be side-stepped by assuming the invasion is not an alien one, but instead a hypothetical human interstellar empire attempting to invade a human colony world. The motivation of the empire can be something stupidly human like "gotta collect 'em all!". This is actually the motivation in Larry Niven and Jerry Pournelle's The Mote In God's Eye. In that novel, there once was a loosely allied human interstellar empire that collapsed in a bloody secession war. The new imperium rose from the ashes, grimly determined that such wars will not happen ever again, and all human worlds must be incorporated into the empire with no exceptions.
If one must have aliens invading because they want some crucial resource, I like to use an analogy. Ordinary resources are not worth it. I don't care what you saw in the TV show V, Markus Baur points out that aliens invading Terra to steal our water makes about as much sense as Eskimos invading Central America to steal their ice. The same goes for gold, uranium, or our women. But what if we hand-wave an unknown resource, something that our scientists have not even discovered yet? (Wow, Zzazel! Their planet is incredibly rich in polka-dotted quarks!)
Then us poor humans will find ourselves in the same spot as a primitive African tribe who does not understand why these Western stranger want to bulldoze their village in order to dig up the dirt. The westerners tell the tribesmen that the dirt is called "Coltain", from which they can extract something called "Tantalum", which is absolutely vital for something called a "Cell Phone." But to the tribesmen, it looks just like the same dirt that is everywhere else, and more specifically, in places that are not under their beloved village. This causes hard feelings, but unfortunately the westerners have something else called "automatic rifles".
For an in-depth look at the topic, go to the indispensable Future War Stories.
If the concept of a huge cannon indirectly attacking targets over the horizon is "artillery", the concept of attacking planetary ground targets from orbit is "ortillery." (term was invented by Game Designer's Workshop)
While it is possible to target the enemy even if the only friendly observers are in orbit, accuracy will be much improved if there is a human or robot on the ground close to the target giving target coordinates. These are called artillery observers, spotters, forward observer, fire support specialist, or fister. Though I suppose in this case they will be called ortillery observers instead.
Of course ortillery shares with artillery the ever-present danger of "friendly fire. If your army units are on the planet battling enemy units, and you have ortillery assets in orbit, often you will need to call down ortillery strikes on hostile positions. But there are many assorted failure modes that will result in the strike hitting your units instead. Weapon malfunctions, ortillery operator mistakes, inaccurate target coordinates, there are many opportunities for things to go badly wrong.
At the basic level one drops nuclear warheads. Next one uses kinetic energy weapons such as Project Thor or The Moon is a Harsh Mistress. Next is Colony Drop. Next is Asteroid Bombardment. Next is Relativistic Weapons. Finally there is the Planetary Nut-Cracker.
This is sort of the outer space equivalent of holding the high ground.
Two people throwing rocks at each other is pretty much a fair fight. If one person is on a hill, they have an advantage. And if one person is at the bottom of a well, that's not fair at all. By analogy, it is beyond unfair if one person is in orbit. The lucky one in orbit does not need to use bullets, missiles or nuclear weapons; a nice selection of rocks and boulders will do. Nudge a rock hard enough to de-orbit it, and it will strike with most of the kinetic energy difference between orbit and the ground. The poor slob on the ground, however, has to use huge rockets just to boost weapons up to the level of orbital person. This is called the gravity gauge.
Please note that "unfair" does NOT mean "impossible".
Back in the 1950s, Robert Heinlein and others made a rather startling observation:
However, it might not be quite as bad as Heinlein thought.
Orbiting a string of nuclear weapons aimed at Earth would be an easy way of conquering the world. Or a Lunar missile base. This was why it was outlawed in the SALT II treaty of 1979. Robert Heinlein wrote about this in his novel Space Cadet and the short story "The Long Watch".
Or maybe it wasn't such a good idea in the first place. The blog Tales Of Future Past points out that neither the Moon nor Earth orbital bases turned out to offer any sort of advantage over surface-based missiles. Lunar bases are easy to target, require missiles with huge amounts of delta-V to deliver the nuclear weapon to the target on Earth, and will take days of transit time. Orbital bombs have utterly predictable orbits and can be seen by everybody (unlike ground based missiles), can only be sent to their target at infrequent intervals (unlike ground based missiles), and will require a deorbiting rocket with pretty much the same delta-V as a ground base missile. So what is the advantage? Please note that not all of these drawbacks apply to enemy spacecraft laying siege to Terra.
Attacking spacecraft dropping nuclear weapons would be somewhat like the situation faced by nations threatened by enemy intercontinental ballistic missiles except that in this case the weapons have no boost phase. The discredited Strategic Defense Initiative had all sorts of ideas of how to deal with the problem. For our purposes, ignore any solution that depends upon the boost phase (since there isn't any), space-based programs are "orbital fortresses", and ground-based programs are "planetary fortresses".
Rick Robinson is of the opinion that the gravity gauge is not quite as one-sided as it appears. In an essay entitled Space Warfare I - The Gravity Well he makes his case. The main point is that the orbiting invading spacecraft have nowhere to hide, while the defending ground units can hide in the underbrush.
Back before he was a science fiction author, Dr. Jerry Pournelle was working in operations research at Boeing. There he came up with the concept for Project Thor, aka "Rods from God". The USAF calls them "hypervelocity rod bundles.
(so it is not true that Project Thor was "invented by a science fiction writer", Dr. Pournelle had not yet started his writing career when he created it)
The weapons are rods of tungsten, ranging in size from that of a crowbar to that of a telephone pole (about 12 meters for all you young whipper snappers who have never seen a land-line phone). Each one has a small computer in the rear and control fins on the nose, i.e., they are dirt cheap and can be mass produced. Boost them into orbit, and each one can be deorbited to strike a specific target anywhere on Earth in a few minutes, striking it at about 3 to 9 kilometers per second. This is equal to 1 to 3 Ricks worth of damage, which means the unfortunate target will be on the receiving end of the equivalent of 3 kilograms of TNT for each kilogram of tungsten rod from god. Not bad for a crowbar. Especially since they are not covered under the SALT II treaty.
A 2003 USAF report describes rods that are 6.1 m × 0.3 m tungsten cylinder The report says that while orbital velocity is 9 kilometers pre second, the design under consideration would have slowed down to about 3 kilometers per second by the time it hit the target. The report estimates that the rod will impact with a force of 11.5 tons of TNT. The back of my envelope says that a cylinder that size composed of pure tungsten will have a mass of 8.3 metric tons, but the figures in the USAF report imply that the rod has a mass of 8.9 metric tons. Which is close enough for government work.
11.5 tons of TNT per rod is pretty pathetic, you might as well use a conventional bomb. This is because 3 kilometers per second is 1 Rick, which means each kilogram of rod is equal to one kilogram of TNT, so why not just drop TNT from a conventional bomber?
An article in Popular Science breathlessly suggests that the rods will strike the target at 11 kilometers per second. This is 13.4 Ricks, which will give the rod an impact of 120 metric tons of TNT. That's more like it, now we are getting into tactical nuclear weapons levels of damage. But the article does not explain how the rod is suppose to start at 9 km/s and strike at 11 km/s after being slowed by atmospheric friction. Popular Science left that as an exercise for the reader. Or as proof of questionable research.
The rod is admittedly quite difficult for the enemy to defend against. It is moving like a bat out of hell, er, ah, has a very high closing velocity, and it has a tiny radar cross section.
The trouble is, the "plasma sheath" created by atmospheric re-entry prevents remote control of the rod. Radio cannot pass through the plasma, so the bar has to be inertially guided. Or not. A Russian scientist thinks they have found the key to allowing radio signals to pass through the plasma sheath. A related problem is that anything on the rod that is not made of tungsten is going to want to burn up in re-entry. Things like the guidance computer, sensors, and hypothetical remote control radio.
The main drawback to Project Thor is the prohibitive cost of boosting the rods into their patrol orbits. Of course if you have a space-faring civilization, the rods can be manufactured already in orbit, thus eliminating the boost cost. Which means any planetary nation without a presence in space is going to be at a severe disadvantage, but that is always true.
Another problem is maintaining the rods in orbit. Things are going to break down, so you either have to have a budget to boost replacements or have assets in orbit that can do maintenance.
Finally, no, this is not the same as the Magnetic Accelerator Cannon from the Halo games. That is a coil gun, Project Thor is more like a weaponized version of dropping a penny from the top of the Empire State building.
Predictably, some maniac made a "Rods from God" mod for the game Kerbal Space Program.
As mentioned in the Space War section, nuclear weapons behave quite differently in airless space (and airless planets) than they do in a planetary atmosphere.
On a planet with an atmosphere the x-rays are absorbed by the atmosphere and become thermal radiation and atmospheric blast. The duration of thermal pulse increases with yield from about 1 second for 10 kilotons to 10 seconds for 1 megaton.
In space it is just x-rays and neutrons.
|Percentage of total energy|
|Blast||40% to 50%|
|Thermal Radiation||30% to 50%|
(unless this is a neutron bomb)
|5% to 10%|
In the tables below the range between the detonation point and the affected target is called the "slant range." If the weapon detonates on the ground this is just the ground distance between the target and the explosion. However, nuclear weapons are commonly detonated at some height above the ground to increase their effect. Given the ground range and the detonation height, the slant range can be calculated by using the Pythagorean theorem:
Thermal Radiation Graph
- Explosion Yield is the yield of the nuclear weapon in kilotons. 1,000 kilotons = 1 megaton
- Slant Range is the distance between the target and the detonation point of the weapon, in miles.
- Curves are thermal flux in calories per square centimeters.
The vertical red line is for 1 megaton (1,000 kilotons). Remember these have a pulse duration of 10 seconds.
- 5 to 6 cal/cm2 for 10 seconds will cause second degree burns. (green line)
- 8 to 10 cal/cm2 for 10 seconds will cause third degree burns. (blue line)
- 20 to 25 cal/cm2 for 10 seconds will ignite clothing. (violet line)
The equation is:
Q ≈ 3000 * ( ƒ * τ * Y / D2 )
Q = thermal flux (cal/cm2)
ƒ = thermal energy fraction ( from 0.35 to 0.40 for air bursts, 0.18 for ground bursts)
τ = atmospheric transmission factor (0.6 to 0.7 at 5 miles, 0.05 to 0.1 at 40 miles. Even lower if foggy)
Y = nuclear weapon yield (megatons). Please note the graph above uses kilotons, not megatons
D = slant range (miles)
|Effects||Explosive yield / detonation height|
|1 kt / 200 m||20 kt / 540 m||1 Mt / 2.0 km||20 Mt / 5.4 km|
|Thermal radiation—ground range (km)|
|Third degree burns||0.6||2.5||12||38|
|Second degree burns||0.8||3.2||15||44|
|First degree burns||1.1||4.2||19||53|
A bit less than half the nuclear weapon's energy becomes atmospheric blast. This has two effects: a sharp increase in atmospheric pressure ("overpressure"), and incredibly strong winds. The overpressure crushes objects and collapses buildings. The wind turns lightweight objects into dangerous projectiles.
In the complicated equations for figuring the area that suffers from a given overpressure, the area is proportional to Y2/3 (where Y is the weapon's yield). This is called the "equivalent megatonnage" of a nuclear weapon. Why do we care? The point is that the combined equivalent megatonnage of several low-yield weapons is greater than that of a single weapon with the same total yield. In other words five warheads (2 megatons each) will do more damage to a city than a single warhead (10 megatons).
|20 psi||Heavily built concrete buildings are severely damaged or demolished.|
|10 psi||Reinforced concrete buildings are severely damaged or demolished.|
Small wood and brick residences destroyed.
Most people are killed.
|5 psi||Unreinforced brick and wood houses destroyed.|
Heavier construction severely damaged.
Injuries are universal, fatalities are widespread.
|3 psi||Residential structures collapse.|
Serious injuries are common, fatalities may occur.
|1 psi||Light damage to commercial structures|
Moderate damage to residences.
Window glass shatters
Light injuries from fragments occur.
Note that the same source says you need 40 psi before lethal effects are noted on people, which contradicts the 10 psi entry above. I don't know which to believe.
|Peak overpressure||Maximum Wind Velocity|
|50 psi||934 mph|
|20 psi||502 mph|
|10 psi||294 mph|
|5 psi||163 mph|
|2 psi||70 mph|
The x-axis is the slant range in feet, divided by the weapon yield in megatons rasied to the 1/3 power. Trace upward to intersect the curve, then to the left to find the peak overpressure in PSI.
The curve can be traced approximately by the formula:
z = Y1/3 / D
p = (22.4 * z3) + (15.8 * z3/2)
z = scaled yield (megatons1/3/mile)
Y = weapon yield (megatons)
D = slant distance (miles)
p = overpressure (lb/in2 or PSI)
|Effects||Explosive yield / detonation height|
|1 kt / 200 m||20 kt / 540 m||1 Mt / 2.0 km||20 Mt / 5.4 km|
|Blast—ground range (km)|
|Urban areas completely levelled|
(20 psi or 140 kPa)
|Destruction of most civilian buildings|
(5 psi or 34 kPa)
|Moderate damage to civilian buildings|
(1 psi or 6.9 kPa)
|Railway cars thrown from tracks and crushed|
(values for other than 20 kt are extrapolated
using the cube-root scaling)
Things are more complicated when the detonation point is some distance above ground level.
The primary shock wave expands outward as a sphere from the weapon detonation point. If this is not a ground-burst, at some point the sphere will expand until it hits the ground. The shock wave is reflected upward from the ground. Since the shocked region inside the sphere is hotter and denser than the rest of the atmosphere, the reflected shock wave travels faster than the primary shock wave. For certain geometries, the reflected shock wave catches up with the primary shock wave and the two shock fronts merge. This is called the Mach Stem. The overpressure at the stem is typically twice that of the primary shock wave.
The area the Mach stem passes over is called the Mach reflection region. The area from ground zero to the start of the Mach reflection region is called the Regular reflection region. It only suffers from the passage of two separate shock waves with the standard overpressure. The Mach reflection region suffers the double overpressure caused by the Mach stem.
The chart below plots the regular reflection region and Mach reflection region, given the detonation distance from the ground. To use, you divide the burst height and the distance from ground zero by weapon kilotons raised to the 1/3 power.
For instance, if the weapon had a yield of 1,000 kilotons (1 megaton) and the weapon burst 2,000 feet above ground level, 2000 / (10001/3)
Scaled Height of Burst = burstHeight / yield1/3
Scaled Height of Burst = 2000 / 10001/3
Scaled Height of Burst = 2000 / 10
Scaled Height of Burst = 200
so on the plot for the vertical scale you would use the tick-mark at 200. By the same token, for the horizontal scale, the tick mark for 800 corresponds to 800 * 10 = 8,000 feet (where 10 = 10001/3).
The dotted line shows where the regular reflection region stops and the Mach reflection region begins.
The bulges in the overpressure curves show where you can optimize the height of burst for a given overpressure. For instance, look at the 15 lb/in2 curve. Find the point on the curve that gets the farthest to the right. Trace a line horizontally to the vertical scale and you'll see this happens at a scaled height of burst of 650 feet. For a 1,000 kiloton weapon this is a burst height of 6,500 feet.
In other words, a weapon bursting at 650 scaled feet of altitude will throw 15 PSI of overpressure out to 1,200 scaled feet from ground zero. But a weapon doing a ground burst with 0 scaled feet of altitude will only throw 15 PSI out to 800 scaled feet from ground zero.
|Effects||Explosive yield / detonation height|
|1 kt / 200 m||20 kt / 540 m||1 Mt / 2.0 km||20 Mt / 5.4 km|
|Effects of instant nuclear radiation—slant range (km)|
|Lethal total dose (neutrons and gamma rays)||0.8||1.4||2.3||4.7|
|Total dose for acute radiation syndrome||1.2||1.8||2.9||5.4|
This is the radioactive fallout, radioactive dust that falls from the sky in a long plume extending downwind.
As a general rule, the fallout is dangerous for about one to six months after the bomb blast.
Unless it was a salted bomb, then you are probabably looking at a hundred years or so. A salted bomb whose fallout emitted a dosage of 10 sieverts per hour would need about 25 half-lives to decay to safe levels (i.e., to a dosage below natural background radiation). For example, a salted bomb producing Cobalt-60 would have fallout with a half life of 5.2714 years. 25 half-lives would be 131.785 years. Tantalum-182 has a half-life of only 114.4 days, it would be safe in about 7.8 years.
Air bursts tend to produce lesser amounts of fallout, but which travel at high altitudes and can scatter itself all over the entire planet.
Ground bursts tend to produce more severe levels of fallout, but which only travel relatively short distances from the detonation site (several hundred kilometers). The Castle Bravo 15 megaton nuclear test made a plume about 500 kilometers downwind with a maximum width of 100 kilometers.
Water surface bursts are sort of in-between.
The Wikipedia article stated that the crater of a ground burst would have fallout emitting radiation at a dosage rate of 30 grays per hour, but failed to specify the yield of the weapon.
Details are classified but the best I've found is the theoretical maximum for a neutron bomb is 80% of the energy is neutrons and 20% x-rays. For conventional nuclear weapons it is 80% soft X-rays, 10% gamma rays, 10% neutrons.
This is done by encasing the weapon in a jacket composed of some element that will easily be transmuted into a radioactive isotope by the weapon's neutron flux. Proposed elements for the jacket include cobalt-59, gold-198, tantalum-182, zinc-65, and sodium-24.
A conventional nuclear weapon typically generates fallout that will decay to safe levels in one to six months. A cobalt bomb whose fallout caused a dose rate of 10 sieverts per hour would take about 130 years (25 half-lives) to decay to safe levels (safe levels being defined as "less than natural background radiation").
The name "salted" comes from the expression "sowing the earth with salt".
A dirty bomb might spread a bit of mildly radioactive dust over a building or two.
A salted bomb will spread highly radioactive fallout across half a continent.
The linked Wikipedia article has an overview of the convoluted details, including a useful quote from a 2010 Oak Ridge National Laboratory report on common EMP misconceptions.
This is an old favorite among fans of nuclear weapons, the one everybody shakes their head over and says WHAT THE FLAMING FRACK WERE THEY THINKING??!? You often see it under such names as Project Pluto, Flying Chernobyl, S.L.A.M., The Flying Crowbar, Nightmare Missile, Flying Death Factory, and Armageddon Cruise Missile From Hell.
The original idea was a 1955 version of what we now call a cruise missile. Seeing that this was going to be a part of mutually assured destruction, perhaps even a possible replacement for the Strategic Air Command, the designers wanted SLAM to be long ranged. Very long ranged. Circle-The-Globe-Four-And-A-Half-Times long ranged.
Chemical fuel couldn't possibly fill the bill, the only thing with enough power was nuclear energy. Alas, cruise missiles share the same problem that aircraft and spacecraft have with atomic drives. The three vehicles all suffer from the Every Gram Counts limit so they want to be as light as possible. But anti-radiation shields are the opposite: the heavier the better. If the crew cabin was located far enough away from the reactor, you might be able to get away with using an anti-radiation shadow shield light enough so that the aircraft could actually get off the ground. It is a pity that anybody on the ground the aircraft flew over would be bathed in deadly radiation.
Then some cold-hearted genius in the research department saw how to turn the liability into an asset.
Understand that the SLAM reactor, like all reactors, are not very radioactive. Until the first time they are powered up, then they will emit torrents of radioactive death for centuries.
If the nation goes to DEFCON 1 you launch the SLAM using non-radioactive chemical rockets. These get the nightmare missile out to sea far enough so that no (United States) person was endangered. Then the totally unshielded reactor was powered up. Since the monster had a range of 182,000 km (x4.5 the circumference of Terra) it wasn't going to run out of fuel anytime soon. Especially since it didn't have to lug around a heavy radiation shield. It could fly in a circular holding pattern until nuclear war was initiated or called off, killing nobody with radiation except sea life and any unfortunate fishermen it flies over.
Somebody figured that "radiation in the defense of liberty is no vice". Somebody on Twitter remarked: "So it does fly without core containment, that is some serious Reaver sh*t."
If the war was called off, the SLAM(s) would abort by quenching their reactors and ditching into the (hopefully) deep ocean. Anybody with bright ideas about salvaging US weapons from the sunken SLAMs will have to deal with the radiation from its neutron-activated structure. The SLAM designers might deliberately incorporate cobalt or something similar into the structure as a rude surprise.
But if war is declared, the SLAMs will drop to a stealth wave-hugging altitude and proceed at supersonic velocity toward their designated Soviet targets, with a weapons loadout of 1 to 42 thermonuclear bombs (1@26 megatons, 42@5 kilotons each). 25 megatons is considered to be a "city-killer", though a single bomb that big tends to be a waste of nuclear energy. Since there are no skyscrapers a mile in the air or a mile underground, the most of the spherical nuclear fireball is wasted. It is more efficient to use a pattern of kiloton devices with a fireball about one skyscraper-height in radius.
The SLAM will cross the ocean at an altitude of 35,000 feet, but when it approached the Soviet air detection system it would drop below "radar detection altitude". One source said that was 500 to 1,000 feet, another said 50 feet.
Traveling at Mach 3 at treetop level (15 meters or 50 feet) means that any person standing underneath will be instantly killed by the sonic shockwave alone (they will also be made deaf by the 150 dB sound and given cancer, but these things matter not to a dead person). The thing is also white-hot so there will be a bit of thermal pulse as well, to add insult to injury.
The same cold-hearted genius also figured that after a given SLAM had dropped all its H-bombs it could still do damage by leisurely flying a criss-cross pattern over Soviet territory, irradiating the croplands and people with deadly radiation from the totally unshielded reactor (sowing the ground with salt, radioactive-style). This also meant that the SLAM designers didn't have to worry about preventing radioactive fission fragments from escaping out the exhaust, since it would give you bonus enemy fatalities out of each gram of fission fuel. Which means they didn't bother putting any cladding on the nuclear fuel elements, they are in direct contact with the air.
And if the Soviets managed to shoot down a SLAM, it would auger into the ground at Mach 3, pulverizing the entire reactor and spreading a plume of radioactive fallout rendering the impact region uninhabitable for about the next ten-thousand years. If they fail to shoot it down, it is programmed to crash anyway. Only after it has finished its sterilization criss-cross. The hot reactor elements will mix with the white hot vaporized forward vehicle structure to create a very fine smoke of radioactive uranium oxides. That is, of a fineness to extend the length of the fallout plume. As Scott Lowther puts it: "It'd make Chernobyl look like Three Mile Island."
The mechanical designer faces a challenge. The pressure drop in the direction of the air stream creates a force of several hundreds of thousands of kilograms trying to suck the reactor out the nozzle, which is a bad thing. The materials available to make supporting structures are limited in volume and nature because of neutronic requirements (too much structural metal and the reactor can go critical while it is being assembled) and high temperatures (standard metals will melt).
|Payload compartment dia (in)||55||58|
|Payload compartment len (in)||213||300|
|Total Vehicle Length (ft)||84||88|
|Hot reactor dia (in)||57||46|
|Hot day design Mach|
1,000 ft above sea level
|Hot day design Mach|
30,000 ft above sea level
|Reactor wall temp (°F)||25,000||3,000|
|Max number of warheads||18-24||26|
|Payload weight (lb)||14,000||15,000|
|Missile weight (lb)||55,800||60,779|
|Booster weight (lb)||61,380||67,465|
|Expected missile range (nm)|
1,000 ft above sea level
|Expected missile range (nm)|
30,000 ft above sea level
It is unclear if the expected range is limited by the nuclear fuel elements becoming clogged with neutron poisons, or because the ceramic reactor core crumbled. If the former, there are modern ways around that problem.
I was curious about the radiation dose the SLAM would inflict upon a person on the ground. It was traveling at 50 feet (15 meters) above the ground, near where the lethal dose was absorbed in about 5.76 seconds. But on the other hand the SLAM is traveling at about 1,000 meters per second (Mach 3) so exposure time is very short. I could not intuit whether the person would get a lethal dose or not. This calls for higher math, probably calculus. Unfortunately I failed to learn calculus (Bad Winchell! No rocket for you!). Therefore I used the old Tom Sawyer Whitewash technique.
On Google Plus I poised the question (please pardon the Imperial units):
For lack of a better source, the word problem below was created by me, unqualified though I am. Be told that it may contain unwarrented assumptions and misunderstood numerical values for which I take sole responsibility. Particularly I am assuming that the diagram above is accurate. Use the analysis below at your own risk.
Say there is a Project Pluto nuclear ramjet cruise missile in the area.
Say that forty feet away from it's center the radiation dose is 5×108 Röntgen/hour of gamma rays. Say that 35 feet away from the center the radiation dose is 5×106 Röntgen equivalent physical/hour of neutrons. The radiation falls off as per the inverse square law. Figure that the maximum range that the radiation has effect is about 15,300 feet, or the distance to the horizon.
It is traveling along line A-B where the line is at a constant altitude of 50 feet (tree-top level), at a speed of Mach 3 (which I think is about 3,350 feet per second since that altitude is practically sea level).
Somewhere near that line is point X, on the ground directly underneath line A-B. A poor hapless person is standing there.
At some point the Project Pluto nightmare missile will appear on the horizon, flash overhead at 3,350 ft/s, and vanish on the far horizon. Emitting deadly gamma-rays and neutrons all the while.
Question: What radiation dosage will the poor person at point X suffer?
Remember neutrons Röntgens equivalent physical have an average quality factor of 10.0 so equals an average of 0.096 Sievert. Gamma rays Röntgens have a quality factor of 1.0 so each equals 0.0096 Sievert (one-tenth that of neutrons).
Thank you very much, Peter Schmidt and Simon Smith! Even if the figures and assumptions I supplied you with were incorrect, the technique revealed will be useful elsewhere. I really have to buckle down and learn calculus, and master Wolfram Alpha.
The Acute Radiation Chart says that 5.8 Grays is at the "Death probable within 3 weeks" level, 16 Gy is "Certain death in one week or less" along with the cruel Walking Ghost period, and 2,440 Gy is about thirty times the 80 Gy "Instant coma and certain death in 24 hours".
Peter Schmidt's formula is:
integrate 1/(x-35)^2 * 5*10^6 from x=50 to x=15300, then multiply by 2
35 = distance from SLAM of the reference dosage rate
5*10^6 = Röntgen/hour reference dosage rate value
x=50 = closest distance SLAM comes to person (altitude from ground)
x=15300 = farthest distance SLAM recedes from person (vanishes over horizon)
1/(x-35)^2 = inverse-square law, how radiation intensity varies with distance
which was derived from the word problem stating: Say that 35 feet away from the center the radiation dose is 5×106 Röntgen equivalent physical/hour of neutrons and Figure that the maximum range that the radiation has effect is about 15,300 feet, or the distance to the horizon and at a constant altitude of 50 feet. The units used for distance do not matter, as long as you use the same units for all three variables. The units used for absorbed dose do not matter, the answer will be in the same units.
This is fed into WolframAlpha as value of integral of 1/(x-35)^2 * 5 * 10^6 from x=50 to x=15300, times 2
Let's try it out. For gamma-rays it was 40 feet away from the center of radiation had a dose of 5×108 Röntgen/hour. So we feed into WolframAlpha value of integral of 1/(x-40)^2 * 5 * 10^8 from x=50 to x=15300, times 2 and it returns 1.0 * 10^8 Röntgen/hr.
1.0 * 10^8 Röntgen/hr / 3600 sec/hr * 9.13 sec = dose of 254,000 Röntgen. Which is the figure Simon Smith calculated, so we are golden.
The above figures are for a SLAM flying at 50 foot tree-top level altitude. Other sources suggest it may fly at up to 1,000 foot altitude. This will drastically reduce the radiation dosage on the ground, but how much?
I used Mr. Schmidt's handy formula, substituting "1000" for "50".
It reduces the neutron dose from a death-in-minutes 163 Gy (1,700 R) to a fighting-chance 50%-fatality 2.5 Gy (26 R).
Sadly for the person on the ground the gamma dose went from an instant-death 2,440 Gy (2.54×105 R) only to a death-in-two-days 25 Gy (2,642 R). Immediate disorientation, coma in seconds to minutes, convulsions, and certain death within 48 hours.
Using Ms. Smith's technique if you adopt a certain death dosage of 10 Gy (394,300 R/hr for 9.13 seconds) as your trigger level, this means the SLAM kills pretty much everybody within a half mile (790 meters) radius of the flight path (15,300 ft ⇒ 2,600 ft ⇒ 15,300 ft). And doesn't do the topsoil any good either. Yes, this is narrower than 3/4 of a mile, but it is only a 30% reduction. After all a half mile radius means the SLAM is laying down a path of scorched dead earth one mile wide and thousands of miles long.
The SLAM may fly at a 500 foot altitude instead of 1,000 feet, which will just increase the dosage. I leave the math as an exercise for the reader.
Hold everything. A gentleman named Giorgio Tiburzi contacted me, and has noted some flaws in the above analysis. Please note that the error appears to be me mis-reading the diagrams, it is not the fault of Mr. Schmidt and Ms. Smith. Apparently I gave them incorrect data and incorrect assumptions. Mr. Tiburzi's analysis is below:
CRASHING THE SLAM
(ed note: the radiation exposure is reported in the obsolete unit Roentgens (R). The SI unit is coulomb per kilogram (C/kg). One roentgen equals 0.000258 C/kg )
An important aspect of test flight of a PLUTO vehicle is the hazard that would arise if the vehicle were to crash in an inhabited region. This hazard will be discussed on the assumptions that the reactor operated for 10 hrs at 600 MW immediately prior to the crash, and that essentially all fission products generated were retained.
The crash is assumed to render the reactor highly supercritical such that it disassembles violently and 10% of its fission product inventory escapes to the atmosphere. The fission products generated at impact are due to the fission of less than one gram of U235 whereas 250 grams of U235 were consumed in the previous ten hour period. Therefore the nuclear disassembly is significant only as a dispersal mechanism.
The dose rates arising from direct radiation at various distances and times after collision are given in Table I.
DOSE RATES AT VARIOUS DISTANCES AND TIMES AFTER COLLISION
Time After Collision 1000 Ft 2000 Ft 3000 Ft 4000 Ft 5000 Ft 6000 Ft 1 hour 10,000 R/hr 530 R/hr 50 R/hr 5.7 R/hr 770 mr/hr 110 mr/hr 1 day 900 R/hr 47 R/hr 4 R/hr 510 mr/hr 70 mr/hr 10 mr/hr 1 Week 90 R/hr 5 R/hr 0.4 R/hr 50 mr/hr 7 mr/hr 1 mr/hr
Attenuation of the gamma rays by air accounts for over a three order reduction in intensity at a distance of one mile from the reactor.
Upon collision, some portions of the reactor will ay off with an initial velocity of 3000 ft/sec. These will have a maximum range not in, excess of 2000 ft. The latter value has been confirmed experimentally in ballistic studies of non-aerodynamically shaped bodies of aluminum, steel, and uranium. Initial velocities of 10,000 ft/sec. were attained. Calculations also corroborate the value of maximum range, for frontal drag acts to reduce the initial velocity rapidly and so limit the range.
Other possible mechanisms for exposure to people in the neighborhood of the crash include fallout and immersion in the cloud. To achieve a realistic and yet conservative value for exposure from fallout, micro-meteorological constants which were determined from the KIWI-A (NTS) test run were employed. Also, a particle size was chosen to maximize the deposition rate at different distances; it varied slightly from a diameter of 30 microns. The maximum fallout dose rate, assuming the escape of 10% of the fission products, was 100 mr/hr at 5500 meters from the crash point and 15 minutes after the crash.
Exposure from direct immersion in the cloud is found to be small with respect to the fallout dose. To compare the two, the integrated dose was determined, for the immersion exposure occurs only during transit of the cloud past the downwind point in question while the fallout hazard is very prolonged. Figure 1 shows that the peak dose from cloud immersion is 35 mr at 5500 meters from the crash point. The fallout dose is also maximized here and is 1.7 r.
The direct dose is also shown for a point source. Since there may be dispersal of reactor contents, the curve may shift left or right 2000 ft., or ~600 meters.
It is seen, therefore, that at distances within 3000 meters from the crash point, direct radiation is the most important cause of exposure, while at greater distances fallout is the most important.
If the crash occured in a populated area, an exclusion radius of 3000 meters, or ~two miles is recommended. Great care would be required for closer approach to the vehicle. Aerial surveillance should be conducted with caution.
|Fissionable Core||47.24 in.|
|Core Length||50.70 in.|
|Critical Mass of Uranium||59.90 kg.|
|Avg. Power Density||10 MW/cubic foot|
|Total Power||600 MW|
|Avg. Element Temperature||2,330° F|
This is from material from the Fourth Symposium on Advanced Propulsion Concepts parts i, iii, iii and from Aerospace Project Review Issue Volume 1, Number 5. As always, in the datablocks you see in on the edges of this page the values in black are from the source documents but the values in yellow are not. Yellow values are ones that I have personally calculated, sometimes using questionable assumptions. Yellow values are not guaranteed to be accurate, use at your own risk.
In March of 1965 the Orion program was pretty much over. Nobody was interested in a spacecraft powered by hundreds of atom bombs. In a frantic attempt to keep it alive, General Atomic released a report describing several potential military applications. Hey, Pentagon, here are some great serving suggestions for an Orion! Please don't let the program die.
It didn't work but you can't blame them for trying.
|Pusher Diameter (m)||8||10||12|
|Exhaust Velocity (m/s)||26,700||32,400||36,000|
The applications used all three of the standard Orion engines: eight, ten, and twelve meter pusher plate sizes. Since a nuclear launch was pretty much out of the question, each proposal used a stage of quick-and-dirty solid rocket clusters to loft the Orion to an altitude of 76,200 meters before the nukes started. The liftoff thrust-to-weight (T/W) ratio was 1.8 for all three Orion sizes. The solid rockets got the spacecraft up to 76,200 meters and 2,900 m/sec, the Orion drive kicked it the rest of the way into a 370 km orbit. The back of my envelope says the Orion has to expend 8,300 m/s of delta-V, some of that is aerodynamic drag and gravity drag.
8-meter Orion spacecraft would be lofted by a cluster of seven 120-inch solid rocket boosters, developed from the strap-on solid rockets used on the Titan III launch vehicle. They would have been more powerful than the Space Shuttle solid rocket boosters.
10-meter Orion spacecraft would be lofted by a cluster of four 156-inch solid rocket boosters. These were studied in the 1960s as possible strap-ons for the Saturn V, and as a cluster to replace the first stage of the Saturn Ib.
12-meter Orion spacecraft would be lofted by a cluster of seven 156-inch solid rocket boosters.
When the Orion drive started up at 76,000 m, its T/W was only 0.55. This meant a very ugly gravity tax, but the total payload delivered to orbit was maximized. Who cares about gravity tax, the Orion has delta-V to spare.
From a military standpoint, the Orion drive is attractive not only because of its high thrust and specific impulse. The drive is also resistant to damage. Fussy delicate chemical engines can be disabled with a handgun. Orion drives are built to be tough enough to withstand hundreds of impacts by nuclear explosions at close proximity. A handgun bullet will just bounce off. The enemy will have to use massive weapons in order to dent one of those babies. This is not as big a selling point for NASA, who generally does not have to worry about enemy spacecraft taking pot-shots at them.
For the same reason such drives are very easy to maintain and repair. You don't need needle-nosed pliers and micro-screwdrivers. A sledge hammer and a cold chisel will do. It helps that the engine is made of good ol' simple to fix steel, instead of cantankerous titanium or aluminum.
And unlike nuclear thermal rockets, Orions have very low residual radioactivity. It is safe to go out and work on an Orion drive only a few minutes after the last nuke exploded. Nuclear thermal rockets on the other hand will be unsafe to go near for a few thousand years.
Some of the applications had the Orion spacecraft stationed in space, others had them based on the ground. The former was basically using the Orion drive to loft an outrageously huge military space station into permanent orbit, in one piece. Applications stationed in space could be launched at leisure. Applications stationed on the ground on the other hand were a reaction force. The Orions would sit in their silos "on alert", ready to launch at a moment's notice. For space based system the primary concern is maneuverability and survivability. For ground based systems the primary concern is readiness.
The minor drawback of the Orion spacecraft's titanic mass is there was no practical way to land them back on Terra (short of lithobraking). Once they were launched into space, they stayed there. The crew was rotated by space shuttles or small reentry vehicles. Trying to land under Orion drive power is a very bad idea, especially on a planet with an atmosphere. The ship will be entering the center of each raging nuclear fireball with lamentable results.
STATIONED IN SPACE
- Strategic Weapon Delivery ("Bomber")
- Space Defense
- Orbit Logistics
- Lunar Base Support
- Space Rescue and Recovery
- Satellite Support
- R&D Laboratory
STATIONED ON TERRA SURFACE
- Emergency Command/Control
- Space Interceptor
- Damage Assessment
- Space Rescue and Recovery
- Satellite Support
EMERGENCY COMMAND/CONTROL (ECCS)
|Stage 2 Orion Engine|
|Pusher dia||8 m|
|Exhaust Vel||26,700 m/s|
|Payload Mass||91,000 kg|
|Orion Engine Mass||82,000 kg|
|Dry Mass||172,700 kg|
|Pulse Units Mass||290,300 kg|
|Wet Mass||463,000 kg|
|Total ΔV||26,300 m/s|
|Reserve ΔV in LEO||18,000 m/s|
|Stage 1 Chemical Engine|
|Payload Mass||463,000 kg|
|Wet Mass||2,540,000 kg|
|Total ΔV||3,100 m/s|
|Stack Height||64 m|
|Stack Max Dia||9.1 m|
In case NORAD gets taken out by a dastardly nuclear first strike on the United States, the ECCS Orion was designed to survive in its secret armored launch silo. It would boost into orbit and take over NORAD's functions, coordinating the nuclear retaliation.
Actually the plan was to launch before the enemy bombs actually hit the ground. NORAD can probably predict it will be unlikely to survive an incoming nuclear strike long before the bombs actually arrive.
The ECCS was housed in an 8-meter Orion. The surface geometry was smooth to avoid creating shot-traps, since an enemy would target an ECCS with lots of hostile weapons fire. After expending all those extra nukes to obliterate NORAD the enemy will be obligated to destroy all the ECCS NORAD-back-ups, otherwise they will have wasted all those warheads and have nothing to show for it.
Since the ECCS would operate beyond Terra's magnetosphere, the crew would need radiation shielding from galactic cosmic rays. Not to mention enemy nuclear warheads, possibly including enhanced radiation weapons.
The wet mass was 2,540,000 kg (5,600,000 lbs), of which 91,000 kg (200,000 lbs) was payload (apparently "payload" is the dry mass of the Orion spacecraft, without any nuclear pulse units. At least that's what my calculation suggest). Stack height with solid rocket boosters was 64 m (210 ft) (cluster of seven 120-inch solid rockets) and a maximum diameter of 9.1 m (30 ft). The boosters loft the Orion to an altitude of 76.2 km (250,000 ft). Then the 8-meter Orion engine uses its 2,400,000 N (530,000 lbf) of thrust and 2,750 seconds of Isp to get the rest of the way to a 370 km (200 nautical mile) circular orbit. At this point it would still have a delta-V reserve of 18,000 m/sec (60,000 ft/sec) for further maneuvers. The reserve can be used to provide orbit altitude and plane changes to provide the most effective surveillance coverage and to evade hostile weapon interceptions.
The ECCS will require a silo only slightly larger than a standard ATLAS or TITAN ICBM silo.
The ECCS would carry a crew of from ten to twenty, with lots of advanced surveillance and communication equipment. Average mission was 30 days, with provisions for up to 60 days. Radiation shielding on the order of 244 kg/m2 (50 lb/ft2) would be around all command/control and crew operating station, to protect against galactic cosmic rays and possible hostile enhanced radiation weapons. The structure, life support systems, and attitude jet fuel will provide an additional 244 kg/m2 for a total of 488 kg/m2 (100 lb/ft2). By way of comparison, a storm cellar protecting the crew from a significant solar storm should have at least 5,000 kg/m2.
Several ECCS would be on constant standby in their silos. If nuclear war was immanent one would be launched as a show of force, demonstrating that the US was "not unprepared to defend itself." Along with a diplomatic reminder that there are more ECCS where that came from.
One would NOT be launched if it was only a time of crisis instead of immanent war. That would be provocative, and could precipitate matters. It is difficult to convince the enemy to stand down from DEFCON 2 when you are massing troops on their boarder, so to speak.
Deployed in low orbit allows immediate surveillance coverage of enemy territory and maximum image resolution. Deployed in remote orbits provides broader coverage of the planet's surface and also allows early warning of incoming hostile weapons fire aimed at the ECCS.
|Stage 2 Orion Engine|
|Pusher dia||10 m|
|Exhaust Vel||32,900 m/s|
|Payload Mass||136,000 kg|
|Orion Engine Mass||110,000 kg|
|Dry Mass||246,000 kg|
|Pulse Units Mass||354,000 kg|
|Wet Mass||600,000 kg|
|Total ΔV||29,300 m/s|
|Reserve ΔV in LEO||21,000 m/s|
|Stage 1 Chemical Engine|
|Exhaust Vel||2,880 m/s|
|Payload Mass||600,000 kg|
|Engine Mass||936,000 kg|
|Dry Mass||1,536,000 kg|
|Propellant Mass||2,964,000 kg|
|Wet Mass||4,500,000 kg|
|Total ΔV||3,100 m/s|
|Stack Height||96 m|
|Stack Max Dia||10 m|
Three of these would be placed in geosynchronous orbit to provide constant global surveillance. They would augment their coverage via inter-ship relay. This will allow the ships to randomly change their positions and frustrate enemy weapons interceptions, yet still maintain coverage. One ship will be the "flagship" but others could take over if the flagship is disabled.
The wet mass was 4,500,000 kg (10,000,000 lbs), of which 136,000 kg (300,000 lb) was payload. Stack height with the stage 1 solid rocket boosters was 320 feet (cluster of four 156-inch solid rockets) and a maximum diameter of 96 m (33 ft). The solid rocket booster has a mass of 3,900,000 kg (8,500,000 lbs). At an altitude of 76.2 km (250,000 ft) the 10-meter Orion engine uses its 3,500,000 N (780,000 lbf) of thrust and 3,300 seconds of Isp to get the rest of the way to a 42,162 km (22,766 nautical mile) geosynchronous orbit. At this point it would still have a delta-V reserve of 21,000 m/s (70,000 ft/sec) for further maneuvers, though in theory it is in its forever home.
Actually, since the SSCCS will be launched in leisurely times of peace instead of under the urgent pressures of impending nuclear armageddon, solid rocket boosters are not needed. Instead the more sophisticated (but more time consuming) liquid-fueled Saturn V's S-IC stage could be used. Especially if NASA ever manged to make the S-IC recoverable, which as SpaceX has demonstrated drastically lowers the launch cost. Such a stack would have a wet mass of 3,300,000 kg (7,200,000 lbs).
The SSCCS will require about 3 megawatts with a peak of 9 MW or so for the surveillance and communication systems. This can be provided with RTG or other advanced power source. The crew will number from 20 to 30, with six-month tours of duty. The SSCCS will stay on location for their operational lifetimes, 15 to 20 years. The long lifetimes are due to the fact that upgrading obsolete surveillance and comm systems is a snap when you are using Orion drive cargo ships. No matter how much the replacements weigh. The communication/surveillance section is basically a chassis accepting plug-in replaceable modules.
STRATEGIC WEAPON DELIVERY (SSSWD or "Bomber")
|Stage 2 Orion Engine|
|Pusher dia||12 m|
|Exhaust Vel||36,000 m/s|
|Payload Mass||136,000 kg|
|Orion Engine Mass||170,000 kg|
|Dry Mass||306,000 kg|
|Pulse Units Mass||424,000 kg|
|Wet Mass||730,000 kg|
|Total ΔV||31,300 m/s|
|Reserve ΔV in LEO||23,000 m/s|
|Stage 1 Chemical Engine|
|Payload Mass||730,000 kg|
|Wet Mass||6,800,000 kg|
|Total ΔV||3,100 m/s|
|Stack Height||88 m|
|Stack Max Dia||12 m|
This would require a full blown 12-meter Orion engine, because nuclear missiles are very heavy. And because you want to carry as many as you possibly can.
The wet mass was 6,800,000 kg (15,000,000 lbs), of which 136,000 kg (300,000 lbs) was payload. Stack height with the solid rocket boosters was 88 m (290 ft) (cluster of seven 156-inch solid rockets). At an altitude of 76.2 km (250,000 ft) and a speed of 3,100 m/s (10,000 ft/sec) the 12-meter Orion engine uses its 4,300,000 N (970,000 lbf) of thrust and 3,670 seconds of Isp to get the rest of the way to its patrol orbit. At this point it would still have a delta-V reserve of 23,000 m/s (75,000 ft/sec) for further maneuvers.
- At A the SSSWD boosts into LEO (370 km) with solid rockets and Orion drive. The crew does a systems checkout.
- At B burns into a Hohmann transfer (blue arc)
- At transfer apogee C it burns to circularize the orbit. SSSWD is now in a 190,000 km circular orbit (green circle)
- At D burns to enter Patrol orbit (red ellipse). Orbit has a perigee of 190,000 km and apogee of 410,000 km (a 190,000-410,000 km Terran orbit). The orbital period is 18.9 days
The crew will number 20 or more. A semi-closed ecological system will be used to permit a six-month tour of duty, with an emergency capacity of one year. It would require about 1 megawatt of onboard power for ship systems.
The interesting details about the weapons loadout are either not defined or classified. They are not in the report at any rate. Drat!
Defensive weapons include decoys and antimissile weapons. Defensive weapons are carried because bombers are the enemy's prime targets. The enemy knows that every single strategic weapon a SSSWD carries is a mushroom cloud with their name on it.
The strategic nuclear weapons were to be carried internally to allow easy access for maintenance. That way the technician wouldn't have to wear a space suit. The weapons are probably either megaton-range "city-killer" nukes, or MIRVs of deci-megaton-range. For reference, the original Minuteman-II ICBM carried a 1.2 megaton W56 thermonuclear warhead. The Minuteman-III had a MIRV bus carrying three 0.17 megaton W62 thermonuclear warheads (170 kilotons). Scott Lowther's recreation of the SSSWD carries 25 MIRVs, each with three warheads.
The nukes could be launched in either of two ways.  warheads could be mounted on missiles, launched from deep space, and guided to their targets.  the Orion bomber could use its 23,000 m/s of delta-V to enter a close hyperbolic flyby of Terra and release the warheads when near Terra.
On the one hand, the first option means the Orion does not have to get close to the target and be exposed to hostile weapons fire. On the other hand the missiles will have very limited delta-V because you cannot cram a full sized ICBM into the Orion bomber. True, the missiles will start with the Orion's orbital velocity but still. Since the paper cites enemy interceptor missiles requiring a day or two to reach the Orion bomber, presumably any missile the SSSWD launched will require a similar amount of time to reach the enemy cities.
The second option means the Orion bomber has to go into harms way. The up side is it can use its awesome amount of delta-V to deliver the MIRVs ballistically. And it probably can deliver the warheads to the target much quicker than any missile. One can just imagine the enemy generals freaking out at the sight of a three-hundred-ton spacegoing ICBM-farm dive-bombing you at hyperbolic speeds on a trail of freaking nuclear explosions while machine-gunning your continent with city-killer nukes.
According to the paper, a fleet of about 20 spacecraft would be deployed. Presumably this will ensure that there will always be several bombers close enough so that the MIRVs travel time will be short enough to give the enemy a major strategic problem. If my slide-rule is not lying to me, a 190,000 km-410,000 km orbit has an orbital period of 1,635,282 seconds or 18.9 days. With 20 SSSWD evenly spaced, that would have a bomber passing through perigee every 81,764 seconds or every 22.7 hours. I picked 410,000 km as a nice round value "beyond Luna" since the report did not give a precise figure. They might have selected an apogree figure to make a bomber pass through perigee once a day.
Siteing strategic nuclear weapons in deep space would be a major escalation of the nuclear arms race. Such Orion bombers are much more difficult to attack, compared to ICBMs in silos or nuclear submarines. It would require entirely new strategic planning and weapons systems. The high orbits mean that enemy weapons would require a day or more to reach the orbiting Orion bombers. If the enemy wishes to take out the Orion bombers simultaneously with the US ICBM silos and nuclear missle submarines, they will be forced to give the US a day or more of warning time. This sort of spoils the surprise of a first strike. In addition the long warning gives the Orion bombers ample time to take evasive action and/or deploy decoys and antimissile weapons.
On the minus side, such a drastic escalation may panic the enemy into starting a nuclear war before the Orion Bomber network was fully established. If the enemy is only half-panicked, they will probably start a crash-priority project to make their own Orion bomber network.
If the attacker wants to just destroy the defender's civilization but does not want to necessarily make the defenders extinct or render the planet uninhabitable, asteroid bombardment might be just the thing. Now there is the chance of disrupting the ecosystem and rendering the planet temporarily uninhabitable, but at least it won't be radioactive.
Most solar systems have enough asteroids so the ammo is mostly free. All you have to supply is the delta-V to send them at the besieged planet at high velocity.
In a balkanized solar system, this is the reason for each space-faring nation to have their own Spaceguard. The idea is to prevent unauthorized changes in asteroid orbits. The idea for several independant national spaceguards is to keep all the spaceguards honest. Quis custodiet ipsos custodes? and all that.
First off, laser weapons used for ship-to-ship combat in the vacuum of space can use whatever laser wavelength they feel like. But things change if you are using laser cannons on ground targets of a planet with an atmosphere.
Wavelengths shorter than 200 nanometers (ultraviolet, x-rays, and gamma rays) are absorbed by Terra's atmospheric gases (so they are sometimes called "Vacuum frequencies"). Note that once a section of atmosphere has been heated into a plasma by the laser (or whatever) things change. Plasma is transparent to vacuum frequencies while non-vacuum frequences are absorbed.
Understand that a tunnel of plasma is only going to last for a fraction of a section so if you want to put a second laser bolt down it you'd better hurry.
And some wavelengths of infrared are absorbed by water vapor in the air. On Terran type habitable planets, moist air is everywhere. Naturally once the water vapor has been heated into plasma, it isn't water vapor any more. Just oxygen and hydrogen ions. Sadly plasma also absorbs infrared.
The US Navy is exploring the feasibility of using a high energy laser weapon as a ship-borne self-defense system against sea-skimming cruise missile attacks. Since the attenuation of laser energy by the atmosphere is the highest at low altitudes and varies with frequency, the selection of appropriate wavelengths becomes critical for a laser weapon to be effective. A high energy free electron laser (FEL) is suitable for employment in the envisaged role because it can be designed to operate at any desired frequency and, to a degree, is tunable in operation. This study aims to determine the optimal atmospheric windows for high energy, pico second, short pulse lasers.
Suitable wavelength windows were selected from either the Jan 1 or July 1, 2004 spectra for the date with a narrower transmittance window by meeting the following two criteria:
- Transmittance value of at least 90%, 95% and 99% respectively over a 10 km long, 10 m high horizontal path.
- Absorption coefficient value of less than 0.02 per km.
Table 5 summarizes the suitable wavelengths. The first four bands from 0.95 μm to 2.5 μm were able to meet the criteria of at least 90% transmittance and absorption coefficient of not more than 0.02 per km. However, there are no wavelengths in the 3.45 to 4.16 μm band that can meet the two specified criteria. The best wavelength window for this band is chosen for 70% transmission and absorption coefficient less than 0.04 per km.
From Table 5, the optimal wavelength windows for molecular atmospheric absorption are between 1.03 μm and 1.06 μm, and around 1.241 and 1.624 μm. This band provides a transmittance of more than 99%. However, as noted earlier, the main drawback of operating in a lower wavelength band is the strong extinction of energy from aerosol scattering.
Table 5. Suitable wavelength windows for various values of T(z) in μm Wavelength
T(z) > 90%
αabs < 0.01/km
T(z) > 95%
αabs < 0.005/km
T(z) > 99%
αabs < 0.001/km
T(z) > 70% 0.95 to 1.11 μm 0.990 - 1.075 0.992 - 0.998
1.002 - 1.006
1.01 - 1.067
1.030 - 1.060 N/A 1.11 to 1.33 μm 1.230 - 1.260
1.271 - 1.283
1.235 - 1.256 1.241 N/A 1.47 to 1.82 μm 1.530 - 1.680 1.535 - 1.565
1.58 - 1.595
1.610 - 1.660
1.624 N/A 2 to 2.5 μm 2.125 - 2.140
2.220 - 2.245
N/A N/A N/A 3.45 to 4.16 μm N/A N/A N/A 3.91 - 3.94
Summary of suitable wavelength bands for FEL operation for a 10 km horizontal path, 10 m above the ocean with no aerosol extinction.
(ed note: 400 nm equals 0.4 μm)
The possibility of using a laser beam as a ship-borne self-defense weapon has become more feasible with recent advancements in laser technology. The advantages of a high energy laser as a weapon are its key attributes of speed-of-light response, ability to handle fast maneuvering and crossing targets, deep magazine capacity, minimal collateral damage, target identification and adaptability for lethal to non-lethal employment. The attenuation of laser energy by the atmosphere is a result of molecular attenuation and scattering. Atmospheric scattering mainly disperses the energy of the laser beam but molecular absorption heats the atmosphere, reducing the index of refraction and thereby creating thermal blooming. The FEL has potential as a shipborne weapon system because it can be designed to operate at any desired frequency and, to a degree, is tunable in operation. The ability to select an operating frequency greatly enhances the successful propagation of the laser beam through the relatively dense air at low altitudes.
The objective of this thesis was to determine optimal operating wavelength bands for a high energy FEL weapon between 0.6 μm and 4.2 μm using the US Air Force PLEXUS Release 3 Version 2 program to set up MODTRAN 4 Version 2 and FASCODE 3 atmospheric transmission programs. Since PLEXUS and its user interface are export limited, this thesis was restricted to processing the MODTRAN and FASCODE output files. These codes allow for complex atmospheric transmittance and radiance calculations based on absorption and scattering phenomena for a variety of path geometries. The input parameters chosen for the simulation runs are meant to represent likely operational scenarios for ship self defense against a cruise missile attack. The main consideration was a 10 m altitude horizontal transmission path. Korea, Taiwan and the Persian Gulf were the three geographical areas chosen for the study. The effect of a short FEL laser pulse was modeled by convolving a normalized Gaussian frequency spectrum with the MODTRAN and FASCODE transmission and absorption coefficient spectra. The result of the convolution operation averages the transmittance values over a number of wavenumbers. The amount of averaging increases as the length of the FEL pulse decrease.
2. FASCODE Results
The higher resolution 0.1 cm-1 FASCODE was used to conduct further analysis on five selected bands or “windows” found from the MODTRAN results. Using the FASCODE aerosol extinction output file results, absorption coefficients for each wavenumber (or spectral frequency) were calculated. The molecular absorption coefficient is a key parameter for thermal blooming calculations. Data for the absorption coefficient were also used to compute the transmission spectrum for molecular absorption only. Using the transmission spectrum and absorption coefficient graphs, the optimal wavelength bands for employment of FEL at low altitudes were identified and summarized in Table 5. The four main bands of 0.95 to 1.11 μm, 1.11 to 1.33 μm, 1.47 to 1.82 μm, and 2 to 2.5 μm contain quite a number of suitable wavelengths that allow transmittance of at least 90% for a 10 km path and have absorption coefficient values of 0.02 per km or less. For a more stringent requirement of at least 99% transmittance, the suitable wavelength windows are between 1.03 to 1.06 μm and around 1.241 and 1.624 μm. However, the main concern for laser transmission through the atmosphere in the 1 μm region is the strong aerosol extinction.
This is a ludicrous orbital bombardment weapon popular in science fiction in the early previous century. Presumably some cruel little boy incinerated some ants on a sunny day using their magnifying glass, and when they grew up to write science fiction they figured scaling it up would be a good idea. Upscale the ants into enemy cities, and upscale the magnifying glass into a titanic parabolic mirror. In space.
TV Tropes calls it the Solar-Powered Magnifying Glass
The main drawback is the mirror would be a hard-to-miss kilometer wide target possessing all the tensile strength of aluminium foil. One nuclear missile and months of work instantly frizzles up like, well, ants under a magnifying glass.
This material is presented here mostly for its entertainment value.
If the invaders are attacking the planet using relativistic weapons, it is more or less game over. There really is no realistic defense, unless the defenders are a Kardashev type II civilization. The problem is light-speed lag. Since the r-bombs are traveling so near the speed of light, they are only a little bit behind the wave of photons announcing their presence. In other words, you only see where they were, not where they are now. From the target's point of view, they would suffer from the optical illusion of the r-bomb apparently moving faster than light. Before you had time to react, the r-bombs would hit with all their devastating effects.
The thing to keep in mind is that all the energy the r-bomb releases has to be put into it in the first place. It takes an astronomical amount of energy to accelerate an object up to 92% lightspeed. If your civilization has managed to anger another civilization who has access to that much energy, you already know you are in deep trouble.
In the novel, the lunar colony is fed up with the yoke of Terran oppression and stages their very own war of independence. Among their assets is a large external mass driver (called a "catapult") ordinarily used to send shipments of grain back to Terra. The colonists weaponize it, firing cannisters of steel-belted solid rock as orbital bombardment weapons.
If the interstellar conflict in question is all about extermination, with none of that realpolitik nonsense, there is no point in a limited orbital bombardment. Assuming you do not want the planet as a possible colony site, then you might as well nuke the place until it is a black glassy sphere that will glow radioactive blue for the next million years or so. The result will be a cemetery planet object lesson for future alien civilizations to come that the inhabitants really pissed you off (or were some hideous species that was far too dangerous to live).
Have your interstellar bomber dump a hellburner, a planet-wrecker nuclear bomb, a planet-sterilizing torch warhead, a planet-cracker antimatter warhead, or a planet-buster neutronium-antimatter warhead. Or take a bit more time to simply carpet-bomb the planet with old-school nuclear warheads.
You take a sizeable planet which you can spare, somehow transport it into the enemy's solar system, then fly the planet on a collision course with the enemy world. If you really want to splatter the enemy homeworld, you fly in two planets on diametrically opposed courses with the enemy in the middle. Sort of like a hammer and anvil. A cosmic-scale sledge-o-matic.
This is a strictly handwavium space-opera style weapon. Very cinematic but nohow nowhere scientifically possible.
(ed note: in the far future of space opera, all nine worlds of the solar system have been colonized. But one fine day the sun starts to cool off. To avoid a frozen death, the planets resolve to place gigantic atom-blasts on each world, fly the planets out of the solar system, and find a warm young star.
They pass several unsuitable stars, but disaster strikes at the star Antolia. The star is going to go nova. And the natives are rather upset at that. The Antolians attempt to capture the passing Solar planets but are beaten off. However, the copy-cat Antolians put atom-blasts on their planets and set off in hot pursuit. The Solar planets finally find a new home star, but the Antolian planets are coming to invade. What to do?)WE STARED, our triumph frozen. In the telescopes the four Antolian planets were plainly visible, passing Walaz and moving on with mounting speed toward us.
"We must do something!” Hurg cried. "If those Antolian worlds reach this sun and take up orbits around it, it means endless war with them, war that may result in our destruction!”
"We can not stop them from coming on,” Julud said sadly. "I had hoped they would stop their worlds at Walaz, but they are coming on.”
"If there were only some way to stop them before they get here!” Runnal exclaimed.
An idea seared across my brain. "There is a way of stopping them!” I cried. "I can stop them with my world, with Mercury!
"Don’t you understand?” I said. "All of Mercury’s inhabitants can be transferred to other of our worlds and then I’ll take Mercury out and crash it head-on into those four oncoming worlds!”
"Good, and I’ll go with you, Lonnat!” cried Hurg.
"And I too!” said Tolarg, eyes gleaming.
Immediately Julud ordered the transfer of Mercury’s people to other worlds as I requested. All our worlds’ ships swarmed to Mercury and engaged in transporting Mercury’s people to the other planets. It was so tremendous a task that by the time Tolarg and Hurg and I with my assistants in the control-tower were the only people left on Mercury, the four oncoming worlds of the Antolians had almost reached Vira.
Quickly I opened up Mercury’s propulsion-blasts and sent the little planet hurtling out from Vira, back along the way we had come toward the four nearing worlds. Tensely I and Tolarg and Hurg held it toward them. Outside the control-tower were our waiting ships.
Toward each other, booming through space with immense speed, thundered Mercury and the four oncoming worlds. The Antolian worlds loomed larger and larger before us. Then they veered to one side.
"They’re veering! 'They’re trying to escape the collision!” cried Hurg. "It’ll do them no good!” I exclaimed. I swung Mercury aside in the same direction to meet them.
Again the column of four planets veered as they rushed closer, seeking desperately to escape the oncoming doom. Again I swung Mercury to meet them. Then the foremost of the oncoming Antolian worlds loomed immense in the heavens before our rushing planet.
"They’re going to crash!" I cried. "Up and away before they meet!”
"Up and away!” yelled Tolarg and Hurg as we threw ourselves from the control-tower into the ships.
Our ships darted up like lightning. The rushing globe of Mercury was almost to the oncoming sphere of the first Antolian world. And then as we shot away from them into space, they met!
There was no sound in the soundless void, but there was a blinding, dazing glare of light that darkened even the great sun behind us for the moment, and then the two worlds became glowing red, molten, blazing with doom! A wave of force struck through space that rocked our fleeing ships.
And behind the first Antolian world the other three of the column came on and crashed into that glowing mass! One by one they crashed and were destroyed; and then the four worlds were one white hot mass that veered oflF into space at right-angles to Vira and away from it. The four colliding worlds had become a new small sun!
I stared after that receding, dazzling mass. There were tears in my eyes as I watched it move away, with the remains of Mercury in it. Mercury, my world, that I had piloted across the great void through the suns only to hurl it at the last into doom.
Hurg was grasping my arm excitedly. "We’ve won, Lonnat!” he cried. "The Antolians and their worlds destroyed, and Vira ours now for our eight remaining worlds!”
Tolarg held out his hand to me, all mockery gone from his face now. "What you said was right, Lonnat,” he said. "It’s not the size of a planet that measures its importance. Yours has saved us all.”
if your budding "Weakly Godlike civilization" wants to graduate to Kardashev Type II, they have to harness all of the power available from a single star. Presumably the primary around which their homeworld orbits. The obvious technique is to surround the entire blasted star with solar power collectors so not a single solar photon wastefully escapes into deep space. The concept was invented by Olaf Stapledon in Star Maker (1937) and later popularized by Freeman Dyson in his 1960 paper "Search for Artificial Stellar Sources of Infrared Radiation" (abstract). Due to the second law of thermodynamics some of the power is going to show up as waste heat, making the "Dyson Sphere" resemble a red giant star. If astronomers do not look closely they may dismiss an observation of an alien megastructure as "just another boring red giant." Naturally science fiction authors fell in love with the concept so there is no shortage of examples in the literature.
But now that your ultra-civilization has access to around 400 yottawatts of power, what are you going to do with it?
Noted science fiction personage James Davis Nicoll had the answer. He brainstormed the concept of the dreaded Nicoll-Dyson Laser. Take the most practical variant, the so-called Dyson Swarm. Equip each of the swarm satellites with a phased array laser. Now you can emit a planet-frying death ray capable of ending all life on any world within a range of anywhere in the Local Group of Galaxies. Timelag is going to be a huge issue, but anyone who can build a Dyson swarm ought to be able to deal with it.
Naturally, as is always the case with any arms race, things get complicated if a second civilization builds one of these planet-pasteurizers. Or several thousand for that matter. Here on Terra we reacted to a similar situation with the doctrine of Mutual Assured Destruction. I'm sure the ultra-civilizations will cosmically sophisticated interlocking strategies far beyond our mental keen.
III. Blast Modeling
We investigate the activity and immediate aftermath of a planet-destroying laser blast with a series of approximations. We consider our target to be an Earth-analog, and so we use the properties in Table 1 for this planet, with values from Kite et al. (2009). We additionally use approximations of the average temperature of the core and mantle as 6000K and 1270K, respectively. Previous work has already examined the question of the energy needed to destroy a planet in this way, and we use their value of 2 × 1032 J in order to destroy an Earth-like planet (Boulderstone et al., 2011). However, it would not be realistic to treat the superweapon as fully efficient, and so we use values based off of nuclear explosions, where 50% of the energy goes into the kinetic energy of the planet, 35% into thermal radiation that raises the temperature of the planetary material, and 15% into an immediate, short-duration flash of electromagnetic radiation2. The observable energy from the explosion then comes from two components, the immediate release of energy during the explosion (what we refer to as the ’flash’) and the long-term thermal radiation from the debris of the planet (what we refer to as the ’remnant’). For the flash, we treat this as a blackbody with a surface of the Earth that will release all of the energy of this component in 2 seconds, or the equivalent of blackbody radiation for a surface at 106 K. We consider the debris of the planet to be well-mixed and be of a single temperature, and when this is calculated for the total energy, we find it to be a blackbody with a temperature of 29,000K. As this is occurring while the planet is being destroyed, the radius will be increasing, however as the escape velocity is 11 km/s we treat this object as consistent with earth-sized for the immediate aftermath. A more time-dependent examination would require accounting for the debris cloud growing in size, as well as the cooling of the debris (a time scale on order of 100 days if approximated as linear cooling) and changes to the optical depth of the debris cloud.
Table 1: Earth Properties Parameter Value Units Earth mass 5.97 × 1024 kg Earth radius 6.37 × 106 m Core mass fraction 0.325 Specific heat capacity, mantle 914 J K-1 kg-1 Specific heat capacity, core 800 J K-1 kg-1
We show the blackbody curves for the flash and the remnant in Figure 2. We also include a blackbody curve for a Sun-like star at 5800K for comparison. We then convolve each of these blackbody curves with the filter throughputs for LSST. Unsurprisingly considering the high temperatures involved, we see that the most significant contributions from both the flash and the remnant will occur in the bluer bands. We treat the solar-mass star as our reference for calibrating the absolute magnitudes by using the method for determining the absolute magnitude in each band using the method that was outlined in Lund et al. (2015). We then compare the total flux in each bandpass for the Sun and for the flash and remnant in order to get relative magnitudes, followed by absolute magnitudes. An important consideration here is that the radius of the planet must be included in these calculations, and so the remnant is a close analogue of a white dwarf in radius and temperature. The absolute magnitudes that we determine are listed in Table 2. It becomes readily apparent that the remnant is generally no more than 1% of the brightness of a solar-mass star, and the flash is only brighter than a solar-mass star in the u band.
Table 2: Absolute Magnitudes Band Sun Flash Remnant u 7.23 6.53 11.16 g 5.86 6.56 11.00 r 4.49 6.23 10.52 i 4.33 6.67 10.87 z 4.29 6.98 11.13 y 3.70 6.62 10.73
These results are even more constraining than they may appear at first glance. The simulated flash duration is 2 seconds, however LSST will have exposures that are 15 seconds in duration. To correctly get the measured apparent magnitude, this difference in duration has to be accounted for, and the flash will look on order of 2 magnitudes fainter in the 15-second exposures of LSST, meaning that it will be slightly fainter than the star. As an inhabited Earth-analog planet (and, therefore, any planet likely worth destroying) would be expected to be around a solar-mass star, the light from the flash and remnant would have to be of considerable brightness with respect to the host star to be observed, and it does not appear that this is the case.
There are, however, three scenarios that may result in the destruction event still being detectable. The first is if the star and planet are close enough to our Solar System that the planet’s destruction can be angularly resolved. Given that LSST will saturate at 16th magnitude, however, it seems extremely unlikely that any geometry exists where this would be possible. The second is if the planet is orbiting a smaller star. A red dwarf, for example, will be several magnitudes fainter, particularly on the bluer end of the LSST filter set. In this case, the flash, and possibly the remnant, will be brighter than the host star. While red dwarfs have not been the typical stars searched for planets in the past, there is no reason to think that an inhabited planet could not orbit around a red dwarf. Finally, the flash in the u band is still brighter than a solar mass star if it is observed instantaneously. In the case of LSST or other survey, this could also be accomplished by having a shorter exposure time, and so an exposure of 2-3 seconds would mean that any flash from a planetary explosion will be significantly brighter than the host star. In the case of LSST, however, the costs of this change to the observing schedule greatly outweigh this benefit as it would significantly curtail the observations that LSST will be able to make of fainter objects.
When merely burning off a planet is not violent enough, pulp science fiction loves to turn the volume up to 11 with the Nova Bomb. None of this fooling around carpet bombing with nuclear weapons, just induce the primary star to explode and incinerate the entire enemy solar system. Use this when the alien species is so horribly dangerous that it absolutely, positively has to be exterminated 100% overnight. You will be sure none of the enemy species escapes (unless they have one of those pesky "jump-type" faster-than-light starships that are immune to your military blocade).
There are no known scientific ways to cause an instant nova, with the possible exception of a strangelet bomb. And even that may be more handwavium than unobtainium.