A "self-rescue ship" is one where in an emergency, the mission can be abandoned and part of the ship can transport the crew home. NASA usually focused on this option because they did not have the budget for a separate rescue ship to go save the crew (with one or two exceptions). As you can read above, this is RocketCat's preferred option.
But for certain spacecraft emergencies, it is best if the crew and passengers abandon ship in some type of escape craft. This is also better for the science fiction author's dramatic purposes. A good example is when they took Alfred Hitchcock film Lifeboat and re-worked it into the science-fiction TV movie Lifepod.
A "life-raft" is a long endurance device carrying many castaways. Its purpose is to keep the castaways alive until they are found and saved by a rescue ship. It is analogous to a wet-navy life-raft. It is discussed here.
A "lifeboat" or "life pod" is a long endurance device carrying many castaways. Its purpose is to keep the castaways alive until they can travel to a safe haven with their rudimentary propulsion system. It is analogous to a wet-navy lifeboat with a motor. It is discussed here.
A "Reentry capsule" or "escape pod" is a short endurance devices carrying few or one castaway. It is only used to to leave a distress spacecraft if there is a Conveniently Close Planet. The castaway(s) bail out of the distressed spacecraft in the reentry capsule, which immediately heads for the planet and does its best land safely on the surface. It analogous to a parachute on an aircraft. It is discussed here.
As previously mentioned, a "self-rescue ship" is one where in an emergency, the mission can be abandoned and part of the ship can transport the crew home. NASA usually focused on this option because they did not have the budget for a separate rescue ship to go save the crew (with one or two exceptions).
This was seen in the Apollo 13 disaster, when the Command and service module's life-support system was destroyed they used the Lunar module as a "lifeboat" while the ship limped home on a free-return trajectory.
This is an emergency lunar escape vehicle concept, in case an Apollo Lunar Module crashed upon landing. It was designed to be assembled from various parts canibalized from the wreck. Note that in the two-man version, the pilot gets an acceleration chair, but the poor second astronaut is slung under the chair by straps. You can read more about this here, and here.
To reiterate: "lifeboat" or "life pod" is a long endurance device carrying many castaways that generally is not reentry capable. It is analogous to a wet-navy lifeboat. The main difference between a life-raft and a lifeboat is that the liferaft does not have a motor.
The technical term for a life-raft is Bail-Out-and-Wait device (BOW). You use it to escape from an uninhabitable spacecraft and await rescue from a remote source (ground-based or space-based). It has no propulsion module.
The technical term for a lifeboat is a Return-to-Space-Haven Bail-Out-and-Return device (RSH-BOR). It does has a propulsion module with enough delta-V to travel to some space based haven with a habitable enviroment. Do not get it mixed up with the RE-BOR, those have a reentry module.
There are some nifty lifeboat and one man reentry vehicles detailed here.
Christopher Weuve says that a merchant ship's primary piece of damage control equipment is a lifeboat. Keep in mind that he is mostly thinking about damage suffered during wartime due to hostile weapons fire.
If the lifeboat is designed for prolonged use, it would be useful for it to contain equipment to put the people into suspended animation. This will reduce the consumption of air, food, and sanity. The lifeboat Narcissus from the movie Alien had a suspended animation capsule.
However, Jim Cambias raises an important point:
If your science-fiction universe includes some coast-guard like service, it makes even more sense to avoid life boats and instead yell for help and sit tight.
The cold emptiness in her stomach congealed into a knot of tension. This whole voyage was turning into a fiasco. With what she'd learned from Martin—including his mission—there was no way the Navy could make a success of it; in fact, they'd probably all be killed. Her own role as a negotiator was pointless. You negotiate with human beings, not with creatures who are to humans as humans are to dogs and cats. (Or machines, soft predictable machines that come apart easily when you try to examine them but won't fit back together again.) Staying on was useless, it wouldn't help her deliver the package for George Cho, and as for Martin—
Rachel realized she had no intention of leaving him behind. With the realization came a sense of relief, because it left her only one course of action. She leaned forward and spoke quietly. “Luggage: open sesame. Plan Titanic. You have three hours and ten minutes. Get started." Now all she had to do was work out how to get him from the kangaroo court in the wardroom to her cabin; a different, but not necessarily harder task than springing him from the brig.
The trunk silently rolled forward, out from under her bunk, and its lid hinged back. She tapped away at the controls for a minute. A panel opened, and she pulled out a reel of flexible hose. That went onto the cold-water tap on her tiny sink. A longer and fatter hose with a spherical blob on the end got fed down the toilet, a colonoscopy probing the bowels of the ship’s waste plumbing circuit. The chest began to hum, expelling pulses of viscous white liquid into the toilet tube. Thin filaments of something like plastic began to creep back up the bowl of the toilet, forming a tight seal around the hose; a smell of burning leaked into the room, gunpowder and molasses and a whiff of sh*t. Rachel checked a status indicator on the trunk; satisfied, she picked up her gloves, cap, anything else she would need—then checked the indicator again, and hastily left the room.
The toilet rumbled faintly, and pinged with the sound of expanding metal pipework. The vent pipe grew hot; steam began to hiss from the effluent tube, and was silenced rapidly by a new growth of spiderweb stuff. An overhead ionization alarm tripped, but Rachel had unplugged it as soon as she arrived in her cabin. The radiation warning on the luggage blinked, unseen, in the increasingly hot room. The diplomatic lifeboat was beginning to inflate.
The shipping trunk in Rachel’s cabin had stopped steaming some time ago. It had shrunk, reabsorbing and extruding much of its contents. A viscous white foam had spread across the fittings of the cabin, eagerly digesting all available hydrocarbons and spinning out a diamond-phase substrate suitable for intensive nanomanufacturing activities. Solid slabs of transparent material were precipitating out of solution, forming a hollow sphere that almost filled the room. Below the deck, roots oozed down into the ship's recycling circuits, looting the cesspool that stored biological waste during the inbound leg of a journey. (By long-standing convention, ships that lacked recyclers only discharged waste when heading away from inhabited volumes of space; more than one unfortunate orbital worker had been gunned down by a flash-frozen t*rd carrying more kinetic energy than an armor-piercing artillery shell.)
The self-propelled trunk, which was frozen into the base of the glassy sphere, was now much lighter than it had been when Rachel boarded the ship. Back then, it had weighed the best part of a third of a tonne: Now it massed less than fifty kilos. The surplus mass had mostly been thick-walled capillary tubes of boron carbide, containers for thin crystals of ultrapure uranium-235 tetraiodide, and a large supply of cadmium; stuff that wasn’t easy to come by in a hurry. The trunk was capable of manufacturing anything it needed given the constituent elements. Most of what it wanted was carbon, hydrogen, and oxygen, available in abundance in the ship's sewage-processing plant. But if a diplomat needed to get away in a real hurry and didn’t have a potent energy source to hand … well, fission, an old and unfashionable technology, was eminently storable, very lightweight, and didn’t usually go bang without a good reason. All you needed was the right type of unobtanium to hand in order to make it work. Which was why Rachel had been towing around enough uranium to make two or three good-sized atom bombs, or the core of a nuclear saltwater rocket.
A nuclear saltwater rocket was just about the simplest interplanetary propulsion system that could fit in a steamer trunk. On the other side of the inner pressure hull from Rachel’s cabin, the trunk had constructed a large tank threaded through with neutron-absorbing, boron-lined tubes: this was slowly filling with water containing a solution of near-critical uranium tetraiodide. Only a thin layer of carefully weakened hull plates and bypassed cable ducts held the glassy sphere and its twenty-tonne saltwater fuel tank on the other side of the bulkhead, inside the warship. The hybrid structure nestled under the skin of the ship like a maggot feeding on the flesh of its host, preparing to hatch.
Elsewhere in the ship, toilets were flushing sluggishly, the officer's shower cubicle pressure was scandalously low, and a couple of environment techs were scratching their heads over the unexpectedly low sludge level in the number four silage tank. One bright spark was already muttering about plumbing leaks. But with a full combat engagement only hours away, most attention was focused on the ship's weapons systems. Meanwhile, the luggage's fabricator diligently churned away, extruding polymers and component materials to splice into the lifeboat it was preparing for its mistress. With only a short time until the coming engagement, speed was essential.
Subvocalizing again: “Luggage. Query readiness state."
"Lifeboat closed out for launch. Fuel storage subcritical and ready. Spare reaction mass loaded. Oxygen supply nominal. Warning, delta-vee to designated waypoint New Peterstown currently 86 k.p.s., decreasing. Total available maneuvering margin 90 k.p.s." That would do, she decided. The saltwater rocket was nearly as efficient as an old-fashioned fusion rocket; back home, it would do for an Earth-Mars return trip, surface to surface. This was pushing it a bit‐they wouldn't be able to ride it back up into orbit without refueling. But it would do, as long as‐
She swallowed, glanced at Martin and blinked twice, the signal for “hold your breath." “Luggage: prep for launch. Expect crew arrival from one hundred seconds. Launch hold at T minus twenty seconds from that time." Once they burned that particular bridge and jumped overboard, all she could do was pray that the bridge crew wouldn't dare light off their radar—and risk warning the Festival—in order to find her and kill her. The lifeboat was a soap bubble compared to the capital ships of the New Republican naval force.
(ed note: After some diversionary explosions and a running gun battle, Rachel and Martin manage to make it back to the secret lifeboat. Rachel is knocked unconsious but wakes up inside the boat.)“A minute ago," said Martin. “What's happened in here?” He was in the couch next to her. The capsule was claustrophobically tiny, like something out of the dawn of the space age. The hatch above them was open, though, and she could just see the inner door of her cabin past it. “Hatch, close." I said I had a lifeboat, didn't I?"
“Yeah, and I thought you were just trying to keep my spirits up." Martin's pupils were huge in the dim light. Above him, the roof of the capsule began to knit itself together. “What's going on?"
“We're sitting on top of—" She paused to pant for breath. “Ah. Sh*t. On top of—a saltwater rocket. Fission. Luggage full of—of uranium. And boron. Sort of unobtanium you need in 'mergency, stuff you can't find easily. My little insurance policy."
“You can't just punch your way out of an occupied spaceship! " Martin protested.
“Watch me." She grimaced, lips pulling back from her teeth. “Sealed—bulkheads. Airtight cocoon 'round us. Only question is—"
“Autopilot ready," announced the lifeboat. An array of emergency navigation displays lit up on the console in front of them.
“Whether they shoot at us when we launch."
“Wait. Let me get this straight. We're less than a day out from Rochard's World, right? This—thing—has enough legs to get us there? So you're going to punch a neat hole in the wall and eject us, and they're just going to let us go?"
“ ‘S about the size of it," she said. Closing her eyes to watch the pretty blue displays projected on her retinas: “About ten thousand gee-seconds to touchdown. We're about forty thousand seconds from perigee right now. So we're going to drift like a t*rd, right? Pretend to be a flushed silage tank. If they light out their radar, they give themselves away; if they shoot, they're visible. So they'll let us go, figure to pick us up later 's long as we get there after they do. If we try to get there first, they'll shoot…"
“You're betting the Festival will finish them off." (a Kardashev type 1.5 civilization in the area)
“Yup," she agreed.
“Ready to arm initiator pump," said the autopilot. It sounded like a fussy old man.
“M' first husband," she said. “He always nagged."
“And here was me thinking it was your favorite pet ferret." Martin busied himself hunting for crash webbing. “No gravity on this crate?"
“ ‘S not a luxury yacht."
Something bumped and clanked outside the door. “Oh sh*t."
“We launch in—forty-two seconds," said Rachel.
“Hope they give us that long." Martin leaned over and began strapping her into the couch. “How many gees does this thing pull?"
She laughed: it ended in a cough. “Many as we can take. Fission rocket."
“Fission?” He looked at her aghast. “But we'll be a sitting duck! If they—"
“Shut up and let me work." She closed her eyes again, busy with the final preparations.
Sneak was, of course, of the essence. A fission rocket was a sitting duck to a battlecruiser like the Lord Vanek; it had about four hours’ thrust, during which time it might stay ahead—if the uncompensated acceleration didn't kill its passengers, and if the ship didn't simply go to full military power and race past it—but then it was out of fuel, a ballistic casualty. To make matters worse, until she managed to get more than about ten thousand kilometers away from the Lord Vanek, she’d be within tertiary laser defense range—close enough that the warship could simply point its lidar grid at the lifeboat and curdle them like an egg in a microwave oven.
But there was a difference between could and would which, Rachel hoped, was big enough to fly a spaceship through. Activating the big warship’s drive would create a beacon that any defenders within half a light-minute or so might see. And torching off the big laser sensor/killer array would be like lighting up a neon sign saying INVADING WARSHIP—COME AND GET ME. Unless Captain Mirsky was willing to risk his Admiral’s wrath by making a spectacle of himself in front of the Festival, he wouldn't dare try to nail Rachel so blatantly. Only if she lit off her own drive, or a distress beacon, would he feel free to shoot her down—because she would already have given his position away.
However, first she had to get off the ship. Undoubtedly, they’d be outside her cabin door within minutes, guns and cutters in their hands. The weakened bulkheads between the larval lifeboat and the outer pressure hull were all very well, but how to achieve a clean separation without warning them?“Mech one. Broadcast primary destruct sequence."
“Confirm. Primary destruct sequence for mech one."
The transponder in her luggage was broadcasting a siren song of destruction, on wavelengths only her spy mechs— those that were left—would be listening to. Mech one, wedged in a toilet's waste valve in the brig, would hear. Using what was left of its feeble power pack, it would detonate its small destruct charge. Smaller than a hand grenade—but powerful enough to rupture the toilet’s waste pipe.
Warships can’t use gravity-fed plumbing; the Lord Vanek’s sewage-handling system was under pressure, an intricate network of pipes connected by valves to prevent backflow. The Lord Vanek didn’t recycle its waste, but stored it, lest discharges freeze to shrapnel, ripping through spacecraft and satellites like a shotgun loaded with ice. But there are exceptions to every rule; holding waste in tanks to reduce the risk of ballistic debris creation was all very well, but not at the risk of shipboard disaster, electrical short circuit, or life-support contamination.
When Rachel's makeshift bomb exploded, it ruptured a down pipe carrying waste from an entire deck to the main storage tanks. Worse, it took out a backflow valve. Waste water backed up from the tank and sprayed everywhere, hundreds of liters per second drenching the surrounding structural spaces and conduits. Damage control alarms warbled in the maintenance stations, and the rating on duty hastily opened the main dump valves, purging the waste circuit into space. The Lord Vanek had a crew of nearly twelve hundred, and had been in flight for weeks; a fire spray of sewage exploded from the scuppers, nearly two hundred tonnes of waste water purging into space just as Rachel's lifeboat counted down to zero.
In the process of assembling her lifeboat, the robot factory in Rachel’s luggage had made extensive—not to say destructive—changes to the spaces around her cabin. Supposedly solid bulkheads fractured like glass; on the outer hull of the ship, a foam of spun diamond half a meter thick disintegrated into a talc-like powder across a circle three meters in diameter. The bottom dropped out of Rachel's stomach as the hammock she lay in lurched sideways, then the improvised cold-gas thrusters above her head kicked in, shoving the damply newborn lifeboat clear of its ruptured womb. Weird, painful tidal stresses ripped at her; Martin grunted as if he’d been punched in the gut. The lifeboat was entering the ship’s curved-space field, a one-gee gradient dropping off across perhaps a hundred meters of space beyond the hull; the boat creaked and sloshed ominously, then began to tumble, falling end over end toward the rear of the warship.
On board the Lord Vanek, free-fall alarms were sounding. Cursing bridge officers yanked at their seat restraints, and throughout the ship, petty officers yelled at their flyers, calling them to crash stations. Down in the drive maintenance room, Commander Krupkin was cursing up a blue streak as he hit the scram switch, then grabbed his desk with one hand and the speaking tube to the bridge with the other to demand an explanation. Without any fuss, the warship's drive singularity entered shutdown. The curved-space field that provided both a semblance of gravity and shielding against acceleration collapsed into a much weaker spherical field centered on the point mass in the engine room—just in time to prevent two hundred tons of bilgewater, and a twenty-tonne improvised lifeboat, from hammering into the rear of the Lord Vanek's hull and ripping the heat exchangers to shreds.
(ed note: Doing some pointless calculations, and linear interpolation of nuclear enrichment of uranium tetraiodine, my slide rule says:)
NSWR Lifeboat Fuel 20.4% enriched
Exhaust Velocity 91,780 m/s Specific Impulse 9,360 sec Uranium Tetraiodide Fuel Mass 250 kg Fuel/Propellant water solution of 2%
Fuel/Propellant Mass 12,500 kg Dry Mass 7,500 Wet Mass 20,000 kg Mass Ratio 2.66 ΔV 90,000 m/s
There is a good description of lifeboats in the eponomously named novel Lifeboat (AKA Dark Inferno) by James White.
The NTR passenger rocket's habitat module spins on its axis for artificial gravity. Since the rocket's designer failed to consult with Mr. Cambias, in the event of a nuclear engine disaster the crew and passengers escape in lifeboats.
The hatch to each lifeboat are set in the floor of the habitat module. The lifeboats are cylindrical but inflate into spheres once they are clear of the ship. At the top is the pressure hatch. 2.4 meters below the hatch is a plastic bag containing lightweight screens used for dividing the inflated pod. Below that is the service module and food store. While uninflated, the walls are folded with convolutions projecting inward. When inflated each lifeboat is three meters in diameter. The upper half of the sphere is transparent, the lower half is covered in reflective foil as a sun-screen.
The service module contains a two shot pre-measured solid rocket, a radio, one heavy set of sunglasses, and a lifesupport system. The lifesystem contains the breathing mix equipment, thermal control, toilet, and water reclamation.
The first passenger jumps into the pod. They then press backward into the side wall and raise their hands to help the next passenger into the pod. The second passenger does not jump, instead they sit on the edge of the hatch with legs dangling down while gripping the hatch coaming with both hands. The first passenger grabs the second's legs and helps them down. They both press backward and the second passenger helps the third in the same way. Three passengers is what the lifeboat lifesupport system is rated for. Passengers are warned to leave behind anything made of metal or having sharp edges, which could puncture the lifeboat walls.
The lifeboats are ejected radially perpendicular to the habitat module's spin axis, at a velocity of 2.45 m/s (1/4 g). Under normal conditions, each lifeboat's umbilical power line is remotely severed before ejection. In the event of a ship control failure, the umbilicals will not be severed, and will give each lifeboat an off-center tug as they separate. This will cause the lifeboats to slowly tumble. If there is an crewperson available, they can manually sever the umbilicals.
The crew cabins eject as four wedge shaped sections. Since they are closer to the spin axis than the floor of the passenger module, the ship's spin has to be increased so they too will be ejected at 2.45 m/s. The medical officer's cabin has a radio powerful enough to reach all the passenger lifeboats, since the officer will have to offer medical advice.
A radio beacon is left behind to designate the rendezvous point.
If a lifeboat is tumbling, the passengers can arrest the tumble by crawling. Lie flat on the transparent section of the lifeboat skin while holding the moulded finger-grips. Rotate their body until the Sun appears to be coming from the top of your head, passing in front of you, and then moving under your feet. Then start crawling in as straight a line as possible. When you come to the lock section or the services panel, or when you are crawling over plastic, which is not transparent, try to keep your line of movement straight by looking ahead to the next transparent section to see where the Sun is. Gradually the tumble will stop. If the Sun is moving too fast to see, blink as fast as you can to visually slow it down. If there is more than one passenger in the pod, they can help by crawling along the same line, evenly spaced around the interior wall. Or even hold on to each other with feet on the walls and heads near the center, and walk in the proper direction.
The desired attitude of each lifeboat is with zero tumble, and the silver section of the wall aimed at the Sun.
The ship proper, still under thrust, leaves the rendezvous point. Once the ship is safely away (after a few days), each lifeboat burns a pre-measured solid rocket to reverse their vector. The engine is oriented so that the thrust axis is aimed at the rendezvous point. The "A" pre-measured rocket is burned for 4.9 m/s of delta V. This cancels the 2.45 m/s outward vector, and gives a 2.45 m/s inward vector in the direction of the rendezvous point.
If the radio beacon is operational, orienting a lifeboat in the proper direction is easy, using fancy electronics.
If the disaster renders the beacon inoperable, the passengers in the lifeboats have to do orientation the hard way. The navigation officer will calculate the reference stars for each lifeboat. The stars will be in a plane perpendicular to the desired vector. The boat's passengers will have to orient such that the line of demarcation between the transparent and the silvered skin hemispheres touches each of the reference stars. They use the same technique used to arrest lifeboat tumble: by crawling on the skin. The officer will have to teach the passengers enough constellations so they can identify the reference stars. Failure to properly orient the lifeboat will probably doom the occupants.
The navigational officer will give each specific lifeboat a precise count-down to igniting the "A" pre-measured rocket.
When the lifeboats near the rendezvous point, the lifeboat will orient itself so that the thrust axis point away. Then on command from the navigational officer they burn the "B" pre-measured rocket and come to a halt. The rocket gives a delta V of 2.45 m/s, cancelling their vector. In this case the proper orientation of the lifeboat is secondary to igniting the B rocket at precisely the correct time. Improper orientation will merely result in a small amount of lateral drift. Improper timing means the lifeboat could stop way short or way past the rendezvous point, possibly even far outside the rendezvous area.
At the rendezvous point they will meet the rescue ship.
The life support section can supply breathable atmosphere enough for three people for two weeks (42 person-days).
The life support section can handle the body heat of up to three adults. Past that the environment will become hotter. Passengers should avoid exertions and remove some clothing in order to prevent heat build up.
The food supply is low-residue and highly concentrated. This is to avoid straining the toilet. The lack of bulk will mean the passengers will always be hungry even though there is enough nourishment to keep them alive. There is enough food for three persons to last two weeks (also 42 person-days).
Water is reclaimed from the toilet and atmospheric humidity. It is more pure than most tap water, but passengers might detect a psychosomatic stink from it if they dwell too much on its source.
For you ugly Americans who have not heard of Perry Rhodan, it is a German science fiction series that has been steadily published installments since 1960 (more than 2,850 as of April 2016). Pretty much the most successful science fiction book series ever written.
To reiterate: A "Reentry capsule" or "escape pod" is a short duration devices carrying few or one castaway that allows them to bail out of a spacecraft in orbit around a planet and safely land on the surface. It is much like a parachute on an aircraft. Except when you pull the ripcord on one of these things the fall will be about two orders of magnitude higher.
The technical term for a reentry capsule is Return-to-Earth Bail-Out-and-Return device (RE-BOR). They include a reentry module. Do not confuse them with RSH-BOR, those have a propulsion module but no reentry capability.
Note that all of the reentry capsules shown here rely heavily upon aerobraking, they would not work on an airless planet or moon. For that the reentry capsule will need seriously large engines and propellant tanks (i.e., you need a full lander). On the plus side any planet or moon with no atmosphere will also have lower gravity. In our solar system the largest airless body is the planet Mercury, and its surface gravity is only 0.38 of Terra. This will reduce the propellant required.
Under the heading of "some people have too much free time on their hands", there are a few science fiction stories featuring bored people using reentry capsules as a sport, much like sky-diver do today. Jumping out of a perfectly good spacecraft. Adrenaline junkies will always be with us.
A deluxe reentry capsule will also contain a survival kit. There are two basic types:
Hostile environment survival kit: those kits that assist survival on nasty deadly planets that will kill unprotected humans in a few seconds. Non-habitable planets, in other words.
A first-aid kit and other medical gear which are useable by an untrained person. You can assume a nurse or doctor will have their own full medical kits.
Making a survival kit for a planet with an enviroment lethal to an unprotected human is incredibly difficult. An castaway using a reentry capsule to land on Terra might wind up in unpleasant places such as a jungle, desert, or ocean; but at least they will have access to unlimited amounts of breathable air. Maybe even food and water. A castaway landing on Mars will not be so lucky. Just ask Mark Watney.
Basically the kit will have to include a pup tent sized habitat module with an entire life support system (Poul Anderson called them "sealtents"). Might as well just make the reentry capsule into a freaking spacecraft. It will probably take the form of some type of inflatable habitat module.
Alternatively you'll need compact equipment to re-fill your space suit's oxygen tanks (and make more O2). Meaning your space suit will be your habitat module. I hope the suit has sanitary facilities or it is going to be really nasty as the suit fills up with poop.
In a paper entitled An overnight habitat for expanding lunar surface exploration by Samuel S. Schreiner et al is described a piece of equipment that could be adapated into a hostile enviroment pup-tent. The item was intended only to be an overnight habitat used for eight hours or so, but it is a start.
The system is intended to enable two astronauts, exploring with an unpressurized rover, to remove their space suits for an 8-h rest away from the lunar base and then conduct a second day of surface exploration before returning to base. This system is composed of an Environmental Control and Life Support System (ECLSS) on the rover, an inflatable habitat, a solar shield and a solar power array...
...The mass, volume, and power analyses of each subsystem are integrated to generate a total system mass of 124 kg and a volume of 594 L, both of which can be accommodated on the Apollo Lunar Roving Vehicle with minor improvements.
The rover ECLSS connects to the habitat via umbilical cables to maintain the atmosphere in the habitat. A thermal control unit on the rover is connected to the liquid cooling garments worn by the astronauts to provide active thermal control, while a solar shield is used to provide passive thermal control to minimize the load on the thermal control unit. The ECLSS contains a carbon dioxide scrubber, a “slurper” to remove humidity, an oxygen tank for respiration, and a water tank for the sublimator, crew hydration, food preparation, hygiene or medical use. The solar array provides power for the overnight system and recharges the rover batteries for the second day of exploration...
2.1. Inflatable ribbing concept
When the astronauts first enter the inflatable habitat, the airlock volume requires a support structure in order to retain its internal shape while at zero internal pressure. Inflatable ribbing may be chosen for structural support. This ribbing consists of a frame of small-diameter inflatable tubes that, when inflated to high pressure, provide a rigid structure for the habitat. Thus, the astronauts can inflate the ribbing prior to entry without filling the interior of the habitat with O2. Then the astronauts can enter the habitat, close the airlock, and fill the interior of the habitat to the desired pressure. A similar inflatable ribbing concept is used in commercially available inflatable camping tents.
2.2. Flexible membrane airlock design
To reduce the total size of the habitat, a novel flexible membrane was designed such that the same internal volume could function as both an airlock and habitat. As shown in Fig. 3, a thin, flexible, airtight membrane divides the internal habitat volume into an airlock side (left) and a habitat side (right). The membrane material is similar to the habitat outer surface without the micrometeorite protection, resulting in approximately 1/4 the surface density. The membrane is sized such that at any given time the entire volume can be used either as an airlock or as a habitat.
The concept of operations for entering the habitat using the flexible membrane airlock is illustrated in Fig. 3. After the astronauts have entered the habitat and pressurized the airlock, they remove their suits on the airlock side (top row of Fig. 3). Next, the airlock membrane is moved manually by the astronauts to its neutral transition configuration (middle row of Fig. 3). A valve in the membrane is used to regulate air flow from one side of the habitat to the other while the membrane is moved and the flow path is filtered to ensure that lunar dust is not transferred from the airlock side to the habitat side. After moving the membrane to the neutral position (in which it divides the habitat into two equal halves), the astronauts unzip an airtight zipper and proceed to the habitat side through the hole in the airlock membrane. Equipment is passed through in the same way. Next, the airtight zipper is closed and the membrane is manually moved towards the airlock side, maximizing the volume of the habitat side (bottom row in Fig. 3). The astronauts close the valve to the airlock side and then conduct activities within the habitat...
...When considering entry and exit of the habitat, a net could potentially be used to restrain the airlock membrane in its neutral transition position in circumstances where the habitat side is pressurized but the airlock side is not. With a net in place, only partial venting of the volume would be required for entry and exit. The flexible membrane concept makes efficient use of the available space and reduces the total required internal volume of the habitat.
2.3. Inflatable geometry optimization
A preliminary geometric analysis was used to select a cylindrical geometry with hemisphere end caps and a flat floor. The cylinder was designed to accommodate the two astronauts standing vertically to don/doff their suits and the two astronauts sleeping side-by-side. The design was further constrained to a minimum interior volume of 12 m3 as a conservative estimate , and was required to have a flat cylinder wall between the end caps that was long enough to accommodate a door 0.75 m wide for entry and egress. The radius of the cylinder, the width of the flat floor, and the length of the cylinder were optimized to ensure that these requirements were met while minimizing the total mass of the inflatable skin and ribbing...
Table 1. Optimal inflatable pill mass and volume Component Mass
Support ribbing 1.10 0.09 0.0007 Adjustable airlock 4.04 1 0.0160 Wall/ceiling 26.27 5 0.1117 Floor 3.60 4 0.0155 Packed volume – – 0.2879 Total 35.01 – 0.1440
Table 2. The optimized geometry of the inflatable cylindrical flat-floor habitat Cylinder radius 1.29 m Cylinder flat side length 0.75 m Maximum floor width 1.80 m Maximum floor length 2.55 m Maximum height 2.21 m Interior volume 12.00 m3 Door height 1.84 m
2.5. Inflatable deployment and stowing
...Using the packaged volume of 0.2879 m3 determined in Section 2.3 (packing factor of 2), the folded inflatable can be expected to fit into a rectangular prism of dimensions 1.4 m×0.7 m×0.294 m...
4. Environmental Control and Life Support Systems
To enable an overnight stay on the lunar surface, the system needs to provide a suitable environment and consumables such as water and food. To meet this need, an Environmental Control and Life Support System (ECLSS) was designed to support two astronauts during the overnight stay and to recharge the astronauts׳ Portable Life Support Systems (PLSS) for a second day of exploration. The demands of the first day were not included in the system design because they would be met by the astronauts׳ (PLSS)...
Table 5. Oxygen and water requirements and storage system sizing for the overnight mission Consumables storage Oxygen Water Quantity required (kg) 8.1 23.9 Tank mass (kg) 6.8 4.0 Tank volume (L) 99.9 23.9
6. Results: system mass and volume estimates
Mass Breakdown ECLSS 28.5 kg Emergency Power 2.0 kg Emergency Inflatable Seat 6.0 kg Power 13.2 kg Thermal Shield 4.6 kg Inflatable 35.0 kg ECLSS Consumables 34.1 kg Total 123.4 kg
ECLSS Consumables Mass Breakdown H2O - Med, Hygeine, Food Prep 7.8 kg H2O - Crew Hydration 7.1 kg H2O - Rover Sublimator 5.9 kg H2O - Refill Suit Sublimator 3.9 kg Oxygen for Ribs 1.5 kg Oxygen for Habitat + Respiration 6.6 kg Food 1.3 kg Total 34.1 kg
Volume Breakdown Inflatable Habitat
287.9 L Thermal Shield 4.1 L Power 62.6 L ECLSS 186.0 L Emergency Inflatable Seat
51.2 L Total 34.1 kg
Castaways will need survival skills or they will be facing a real short life-span. They will get to see how good they are at playing Robinson Crusoe or Swiss Family Robinson. Which could be a real challenge if the planet does not have a human-habitable biome.
As the duration on the planet without rescue drags on, the line between castaway and colonist becomes blurred. A few old-timey science fiction stories postulate a "castaway's code" where people marooned on a habitable planet with no hope of rescue must marry each other and found a colony, by law. Left unstated is why such a bizarre law would have been passed in the first place. Rampant imperialism, I guess.
Sometimes space explorers won't crash but will discover a shipwrecked spacecraft or life boat and will do a search for castaways. That is, of course, if it is a Terran spacecraft. If it is extraterrestrial, more caution is needed. If it from an unknown extraterrestrial species, call out the marines and the first contact specialists. And do keep in mind the movie "Alien."
If explorers discover lots of shipwrecked spacecraft, go to red alert because you have apparently discovered a "Sargasso of Space planet". And if you are not real careful you'll be the next shipwreck. Whatever wrecked all those other spacecraft might still be active.
Old pulp science fiction stories sometimes take the slant that deliberately marooning another human on a wilderness planet for the rest of their life is an unspeakable act, the crime of crimes. It doesn't matter if they are your worst enemy, it just isn't done.
More recent science fiction is a bit more cynical. Vaporizing your enemy with a laser pistol is too merciful, marooning them ensures they suffer your maximum revenge as they slowely starve to death.
Novels and short stories that cover the shipwrecked spaceship and castaway theme include:
- The Martian by Andy Weir
- The Moon Is Hell by John Campbell
- Transit of Earth by Arthur C. Clarke
- Enemy Mine by Barry Longyear
- Five Against Venus by Philip Latham
- No Man Friday (aka First on Mars) by Rex Gordon
- The Man Who Lost the Sea by Theodore Sturgeon
- Shipwreck by Charles Logan
Movies that cover the shipwrecked spaceship and castaway theme include:
Equipment used to save untrained civilians in case of a loss of pressure can be found here.
The science fiction suit hinges on some kind of oxygen you can inject into your blood stream to avoid anoxia. Coupled with some kind of suit to provide pressure to avoid Ebullism, Decompression Sickness, Kittinger Syndrome, and other nasty ways that space kills you.
Star Trek predicted something along these lines called "tri-ox compound." The novel Phase Two postulated "dioxo solution." As it turns out there is a real world version of injectable oxygen being experimented with. It only works for 15 minutes but I'm sure that will be improved.
An emergency space suit that can be donned in 30 seconds would be great, but is currently science fiction. And even if such quick-don suits are available, if there is a catastrophic loss of pressure, a crewperson has about 10 seconds max before they go unconsious.
What you need is a tiny cubicle you can jump into, slam the door, and yank the cable to the emergency oxygen tank. In under 10 seconds. An Emergency Shelter in other words. Though to make the situation survivable, the shelter needs to include some sort of space suit.
Such shelters will have to be located at strategic spots in the habitat module. And there should be enough shelters so a hull breech does not trigger a death-race among the crew, where slowest gets to die of hypoxia.
I was wondering how big these Clarke emergency shelters would have to be; since they have to accomodate one crewmember, one space suit, and enough extra room so that the crewmember can actually wiggle into into the suit. On the International Space Station, they use Extravehicular Mobility Units. These separate into two parts at the waist, which means you need lots of room to suit up in one of those things.
The thought occured to me that you can make the emergency shelter smaller if the suit is outside, attached to a Suitport. Then the shelter proper just needs enough space for the crewmember and swinging room for suit's backpack/entryhatch.
A smart person who goes by the handle of ReLuxe made the idea even better. Instead of a rigid cabinet for the emergency shelter, replace it with a Life Support Ball. A rigid cabinet is always the same size, the life support ball deflates down into a flat package. If vacuum strikes a crewmember can leap into the ball, seal it, and inflate with emergency oxygen in under 10 seconds. Now they have an hour to power up the suit, prep it, and squeeze into the blasted thing (donning one of those hinged backpack suits can take about five minutes, mostly squirming into the water cooled long-johns).
He was Gulliver Foyle, Mechanic's Mate 3rd Class, thirty years old, big boned and rough . . and one hundred and seventy days adrift in space. He was Gully Foyle, the oiler, wiper, bunkerman; too easy for trouble, too slow for fun, too empty for friendship, too lazy for love. The lethargic outlines of his character showed in the official Merchant Marine records:
FOYLE, GULLIVER — AS-128/127:006
EDUCATION: NONE SKILLS: NONE MERITS: NONE RECOMMENDATIONS: NONE
A man of physical strength and intellectual potential stunted by lack of ambition. Energizes at minimum. The stereotype Common Man. Some unexpected shock might possibly awaken him, but Psych cannot find the key. Not recommended for further promotion.
He had reached a dead end. He had been content to drift from moment to moment of existence for thirty years like some heavily armored creature, sluggish and indifferent, Gully Foyle, the stereotype Common Man, but now he was adrift in space for one hundred and seventy days, and the key to his awakening was in the lock. Presently it would turn and open the door to holocaust.
The spaceship Nomad drifted halfway between Mars and Jupiter. Whatever war catastrophe had wrecked it had taken a sleek steel rocket, one hundred yards long and one hundred feet broad, and mangled it into a skeleton on which was mounted the remains of cabins, holds, decks and bulkheads. Great rents in the hull were blazes of light on the sunside and frosty blotches of stars on the darkside. The S.S. Nomad was a weightless emptiness of blinding sun and jet shadow, frozen and silent.
The wreck was filled with a floating conglomerate of frozen debris that hung within the destroyed vessel like an instantaneous photograph of an explosion. The minute gravitational attraction of the bits of rubble for each other was slowly drawing them into clusters which were periodically torn apart by the passage through them of the one survivor still alive on the wreck, Gulliver Foyle, AS-128/127:006.
He lived in the only airtight room left intact in the wreck, a tool locker off the main-deck corridor. The locker was four feet wide, four feet deep and nine feet high. It was the size of a giant's coffin. Six hundred years before, it had been judged the most exquisite Oriental torture to imprison a man in a cage that size for a few weeks. Yet Foyle had existed in this lightless coffin for five months, twenty days, and four hours.
On the one hundred and seventy-first day of his fight for survival, Foyle answered these questions and awoke. His heart hammered and his throat burned. He groped in the dark for the air tank which shared his coffin with him and checked it. The tank was empty. Another would have to be moved in at once. So this day would commence with an extra skirmish with death which Foyle accepted with mute endurance.
He felt through the locker shelves and located a torn spacesuit. It was the only one aboard Nomad and Foyle no longer remembered where or how he had found it. He had sealed the tear with emergency spray, but had no way of refilling or replacing the empty oxygen cartridges on the back. Foyle got into the suit. It would hold enough air from the locker to allow him five minutes in vacuum … no more.
Foyle opened the locker door and plunged out into the black frost of space. The air in the locker puffed out with him and its moisture congealed into a tiny snow cloud that drifted down the torn main-deck corridor. Foyle heaved at the exhausted air tank, floated it out of the locker and abandoned it. One minute was gone.
He turned and propelled himself through the floating debris toward the hatch to the ballast hold. He did not run: his gait was the unique locomotion of free-fall and weightlessness … thrusts with foot, elbow and hand against deck, wall and corner, a slow-motion darting through space like a bat flying under water. Foyle shot through the hatch into the darkside ballast hold. Two minutes were gone.
Like all spaceships, Nomad was ballasted and stiffened with the mass of her gas tanks laid down the length of her keel like a long lumber raft tapped at the sides by a labyrinth of pipe fittings. Foyle took a minute disconnecting an air tank. He had no way of knowing whether it was full or already exhausted; whether he would fight it back to his locker only to discover that it was empty and his life was ended. Once a week he endured this game of space roulette.
There was a roaring in his ears; the air in his spacesuit was rapidly going foul. He yanked the massy cylinder toward the ballast hatch, ducked to let it sail over his head, then thrust himself after it. He swung the tank through the hatch. Four minutes had elapsed and he was shaking and blacking out. He guided the tank down the main-deck corridor and bulled it into the tool locker.
He slammed the locker door, dogged it, found a hammer on a shelf and swung it thrice against the frozen tank to loosen the valve. Foyle twisted the handle grimly. With the last of his strength he unsealed the helmet of his spacesuit, lest he suffocate within the suit while the locker filled with air if this tank contained air. He fainted, as he had fainted so often before, never knowing whether this was death.
Sometimes in an emergency situation, the crew will have to deal with people who cannot wear a space suit. This includes people who are too wounded, too unconscious, too untrained, or too stupid to use a suit (or even put one on). It will be useful to have some kind of basic no-frills life support equipment that you can shove the people into and trust it to keep them alive without your attention.
|Oxygen Supply||1 hour|
|Habitable Volume||0.33 m3|
It will also be useful to supplement one's supply of space suits with Personal Rescue Enclosures aka emergency life support balls. These are basically bare essential spherical suits with no arms, legs, or heads for use by people who are injured or untrained in suit operations.
The ball had three layers: urethane inner enclosure, Kevlar middle layer, and a white outer thermal protective cover. The user enters the ball, puts on the oxygen mask, cradled in their arms a carbon dioxide scrubber/oxygen supply box, and a crewperson outside zips it up. The ball would be connected by an umbilical to the shuttle to supply air until the airlock depressurized. Then the oxygen box gives the user one hour of breathable air, while a crewperson tows the ball to safety.
Mercifully the ball included a tiny Lexan window to prevent total sensory deprivation.
When a passenger liner has a problem, the crew members will stuff the passengers into these balls, zip them up, and tow them to safety. And even a person highly skilled in space suits can be a problem if they are unconscious and suffering from a broken arm. It will be much quicker to slip them into a ball instead of trying to suit them up.
For passengers, one would be wise to use balls that cannot be opened from the inside. Passengers can do remarkably silly things at the worst possible moment.
Damage control facilities are generally only found on military vessels. One room will be Damage Control Central (DCC), often near or in the engineering section. This is where the Damage Control Officer coordinates the damage control parties. Generally you want the DCC to be in the section of the ship that is hardest to damage (actually, the second hardest spot to damage. The hardest spot should be occupied by the bridge/CIC).
There may be small damage control lockers sited at strategic locations throughout the ship. Locker contents may include hull patches, emergency power cables (i.e., glorified extension cords), short range radios, testing and sensing instruments, portable emergency power generators, fuses, fire extinguishers and tools. They may also have first-aid kits.
Lockers near the reactor or drive will also include geiger counters or other radiation detection and monitoring gear. The detectors will be mounted on long telescoping rods, so one can poke the detector around a corner or near a suspicious breach without exposing oneself.
On wet-navy ships there is a special damage-control deck, which is the lowest deck with longitudinal breaks in the watertight bulkheads. This allows quick access to all parts of the ship. However, since our ships are tail-landers instead of belly-landers, in place of a damage-control deck might be one or more special ladderways running along the core of the spacecraft.
The cables, pipes, and duct work will either be exposed along the corridors, behind removable panels to protect them from clumsy crew, or accessable via manholes.
If the ship's power grid goes dead, the emergency lighting will go on. This will be red to preserve the night vision of the damage control parties. This means the cables and pipes will be labeled in black text since red lighting makes color coding ambiguous.
Christopher Weuve says that a merchant ship's primary piece of damage control equipment is a lifeboat.
Damage Control Gallery
Primitive spacecraft (like we make today) tend to use lightweight power supplies. Since the one-lung propulsion systems cannot cope with anything massive, not without savagely cutting into the payload mass. But once the state of the art advances, ships become electricity hogs. Especially if they are warships.
While plentiful power is always welcome, it does come at a cost. Besides the fact that they are aglow with lethal radiation, such plants can occasionally become — how can we put it — unstable. Which is real exciting if the plant is using fission, fusion, or antimatter reactions.
Alternatively, a ship could be inexorably heading for a crash landing and you'd just as soon not share the crash site with a reactor going all China Syndrome on you. Or with magnetic cannisters of antimatter fuel, which are much more touchy than nitroglycerin bottles and contain orders of magnitude more bang.
Remember, Jim Cambias said If it's a reactor emergency you're worried about, don't eject the crew in pods, EJECT THE REACTOR!
The point is there has to be some mechanism to quickly quench the power reaction (whatever it is), and render both the reactor and the fuel inert and safe. Or a mechanism to eject the blasted thing and get it as far away as possible.
There will be a SCRAM button to shut down the power plant and a JETTISON button to eject the power plant. Paranoid designers will also have computerized monitoring systems to watch the power plant and automatically push the appropriate button in a fraction of a second.
The term "Scram" means "the sudden shutting down of a nuclear reactor usually by rapid insertion of control rods." Urban myth alleges it came from "Safety Control Rod Axe Man" but this is incorrect.
In many cases powerful rocket engines incorporate dangerous power technologies integral to their design. Just like dangerous power generators, you will need the ability to SCRAM or eject them in emergencies. A good example is solid-core nuclear thermal rockets, which are literally nuclear reactors with the hot working fluid piped to an exhaust nozzle instead of a generator turbine.
NASA had even more worries during the NERVA project. Instead of just worrying about the crew, they also has to worry about the unfortunate inhabitants on Planet Terra who lived near the (radioactive) engine crash site.
I found two interesting reports: Nuclear Rocket Destruct System Requirements by W. H. Esselman of Westinghouse Electric Corporation (Astronuclear Laboratory) and A Destruct System For the NERVA Engine by K. N. Kreyenhagen, W. H. Thiel, and S. K. Yoder of Aerojet-General Corporation. You can find them in this report along with more scary reading. I'll try to give you an executive summary.
For NASA's purposes, there are actually two separate types of engine jettison: pre-operational ("anti-criticality") and post-operational ("disposal"). Or "before you power-up the reactor" and "after you power-up the reactor". Pre-op happens when the chemical booster lofting the nuclear spacecraft into orbit fails mid-flight. Post-op happens when the nuclear spacecraft has been delivered into orbit, is flying around under nuclear power, and suddenly starts to crash on Terra.
You see, a brand-new nuclear reactor that has never been powered-up is actually not very radioactive. After you power-up the little monster it creates all sorts of hideously radioactive radioisotopes in the fuel rods, and neutron-activates nearby structural members exposed to the neutron flux.
What's the difference? Well, for pre-op jettison you eject the engine and use explosive shaped charges to coarsely chop it into sub-critical bits. Bits that will not undergo nuclear fission even if they land in the ocean (water is a great nuclear moderator). A relatively chunky 0.205 grams of U235 per square centimeter (750 grams within a 27 inch diameter circle). The idea is that uranium is relatively harmless, you just want to prevent the blasted stuff from gathering in a critical mass and undergoing nuclear fission. Even if the fuel elements dissolve into goo and start flowing around.
Post-op is different. Now the engine is full of dangerous radioisotopes. To have less than quote "acceptable" unquote levels of contamination, you have to use explosives to finely pulverize the reactor into itty-bitty fragments that will ablate down to less than 25 microns (9.84×10-4 inches) in size by the time they fall down to the 30 kilometer altitude level. The report figures the bits will have to start out at 1 mm in diameter to ablade enough. The report helpfully defines "acceptable" as "no excessive radioactivity returns to a populated area."
They did lots of math that you can read all about in the report to analyse various reactor fragment sizes, see what size it will ablade down to, and calculate the radiation dose it emits. They assumed the nuclear engine operated for 30 minutes at 1120 megawatts. The results are in the table below. The important parts are the last two columns. They figured a dose rate of 0.018 Rads per hour (1.8×10-4 Grays per hour) was acceptable. This translates to an initial fragment size of 1/32 inch (0.79 mm or "about 1 mm").
Now, since the post-op minimum fragment size is smaller than the pre-op fragment size, one would assume that you could use the same post-op explosives system for either type of engine destruct. But you'd be wrong. You see, pre-op the nuclear engine is perched on top of the chemical booster, a gigantic thin-walled tank jam-packed with chemical fuel. NASA safety experts concluded that you want to use the smallest explosive system possible because detonating the chemical booster will make everything worse. And the post-op explosives system is much larger that the pre-op, it will detonate the chemical booster for certain. Bottom line is you'll need two separate explosive systems, one for pre-op and one for post-op.
Shaped charged explosive systems were selected for the design because they had the lowest mass of all the reactor disassembly systems. (It might be worth while to review the difference between a shaped charge and a self-forging projectile, they are similar enough to be confused together, but are quite different in end result. The report tends to use the two terms interchangeably.)
PRE-OP DESTRUCT CONCEPTS
Concept 1 consists of a girdling array of linear shaped charges. When detonated, they cut through the crunchy outside reactor casing and neutron reflector layers, to get at the chewy core in the center. The shock pulverizes the core, and the sliced and diced reactor casing allows the core to disperse. Simple and reliable.
However, the girdle cannot withstand the radiation or the intense heat of normal engine operation. Before you fire up the reactor you have to somehow dismount or discard the girdle, or it will unexpectedly blow up the engine.
Concept 2. My apologies, the image is almost worthless. I think the original was in color. It is supposed to show a conical shaped charge inside the nozzle. Upon detonation it sends a self-forging hypervelocity jet of metal upward through the throat of the nozzle, scoring a direct hit on the bottom of the reactor core. This shatters the core, and hopefully also ruptures the reactor casing so the fuel rods can escape. While this concept is lighter than Concept 1, it is unclear if the shock will be enough to rupture the casing.
Obviously the pilot had better eject the conical shaped charge before firing up the engine or they will get a very rude surprise. The pilot will find the hot exhaust ignites the shaped charge and
shoots them in the a... destroys the engine.
Concept 3 is merging Concept 1 and Concept 2. You reduce the power (and mass) of C1's girdle so it is just strong enough to rupture the casing. C2's up-the-nozzle shot only has to take care of the core. The researchers actually tested this using a steel rocket casing, magnesium bars to simulate reflector segments, and a Titan nozzle. It flew into pieces like a champ. They used 57 kilograms of C-4 plastic explosive for the girdling charge with a cross-sectional area of 29 square centimeters. This actually proved to be over-kill, they wanted to try even smaller charges.
POST-OP DESTRUCT CONCEPTS
This is a challenge. You have to take a 1,360 kilogram core of fuel-enriched graphite and pulverize it into 1 mm particles.
Since the core is surrounded by pyrolitic graphite tiles, support tiles, a lateral support system, graphite reflector barrel, steel barrel, shim rods, coolant channels, tie bolts, beryllium reflectors, control rods, and the aluminum pressure hull, designers have focused on somehow introducing an explosive charge into the core and detonating it in the center. Otherwise the explosive force has to waste energy cutting through all the crap surrouding the core. This is known as the "central burster" concept.
Obviously the explosive charge cannot be resident inside the core during normal operation, for the same reason you do not store crates of dynamite inside a furnace. You have to somehow quickly get the explosive charge into the core and trigger it.
Concept 4 has the explosive charges inside a series of long projectiles. This are stored in launcher tubes above the engine, behind the radiation shadow shield. The latter is because radiation is bad for the explosives. Upon command, the projectiles are launched, penetrate the shield, enter the core, then blow up. They require an impact velocity of 300 meters per second.
The guns or launchers have to be lightweight, reliable, capable of delivering the projectiles simultaneously and capable of detonating the projectiles simultaneously. This is going to cost you lots of mass, "lightweight" is a relative term. If the explosive charges are 14 kg apiece and there are four projectiles, the total mass will be a whopping 680 kg, not counting the control and power source circuitry.
Concept 5 has a series of shaped charges with self-forging warheads that are attached to vertical bars. These are stored above the radiation shadow shield. Upon command, the bars are slowely lowered so they surround the core. Sort of a three dimensional circular firing squad. When detonated they fire hypervelocity jets of molten metal through the stuff surrouding the core and shred the core.
The advantage over Concept 4 is much lower system mass, it is trival to deliver them simultaneously and it is relatively easy to trigger the charges to go off simultaneously. For the same 680 kg system mass, Concept 5 can utilize a hundred or more shaped charges.
Concept 6 uses slabs of plastic explosive instead of racks of shaped charges. The idea is for the explosion to implode the core, crushing it.
RADIATION DAMAGE TO EXPLOSIVES
Nothing really enjoys radiation, and explosives are touchier than most. You do not want the radiation from the engine degrading the explosive's punch nor do you want them to detonate prematurely. A NERVA engine typically produces a dose rate of 105 rad/sec at the side and 103 to 104 rad/sec in the shadow of the radiation shield. So over an operating time of 1,200 seconds the total dose will be from 106 to 108 rads.
Premature detonation happens when the radiation flux heats the explosive by gamma absorption and inelastic scattering. Typically explosives blow up when they reach a temperature of 150 to 200°C. They may not actually explode, but it is almost as bad if the stuff undergoes decompostion or deflagrates. They will not be able to perform their duty. Some coolant may be required.
Explosive degradation happens as radiation breaks chemical bonds in the explosive's molecules. This gradually turns the plastic explosive into just plain plastic. This seems to happen at about 107 to 108 rad which means the radiation shadow shield might provide enough protection. There is some suggestive evidence that cooling helps slow degradation, which is a good thing. Coolant weighs less than radiation shielding.
Self-destruct is a mechanism (protocol or device) that can cause an object to destroy itself on command. The object can be totally blown into smithereens or merely render the object useless if captured by the enemy (the latter is called scuttling). It is rather common in media science fiction since it is so dramatic. That agonizing count-down really ratchets up the tension.
Reasons for including such a device on a spacecraft, space station, or planetary base include:
Most real-world boosters and spacecraft include self destructs to prevent lawsuits and massive negative publicity if the rocket goes off course. Manned rockets generally have some sort of launch escape system to propel the habitat module clear of the blast radius (with the notable exception of the Space Shuttle).
The range safety officer with their finger on the big red button are usually located at some distance from the object they are blowing up. So they will have some objectivity (i.e., not hesitate because they are scared of committing suicide).
If civilian owned spacecraft have propulsion systems frightful enough to be weapons of mass destruction then by law all such ships will be equipped with destruct devices controlled by the Launch Guard. Just in case a tramp freighter with an antimatter engine has a drunk pilot and starts heading towards a major metropolitan area.
Military ships do not have self-destructs for range safety reasons, but they might have them for scuttling purposes. Or because the civilian goverment does not trust the space navy.
The data banks are a treasure trove of valuable information: space navy secret code books, battle plans, task force compositions, etc. If the enemy gets their hands on any of that, the results could be more damaging than losing a battle. All data stores will need some kind of explosive charge or whatever to render the data unreadable. With the charges capable of being detonated on remote command from the CIC or manually by the crew stationed nearby. In the old wet navy the code books had covers made out of lead, to help speed them to Davy Jone's Locker when the captain throws them overboard. That won't work in space.
Building space warships takes such an inconveniently long time. If the enemy captures one of your warships intact they will gleefully replace the crew, hastily paint on their national insignia, and thus instantly have a new (slightly used) unit in their space navy. To prevent that you want to scuttle your ship. You don't have to atomize it, just damage it enough so that its major contribution to the enemy's war effort is as a load of scrap metal.
This is a specialized form of scuttling a captured warship's data banks, where the emphasis is on destroying any star charts you have on board.
If you are super paranoid you might have to destroy the entire ship with crew. It is surprising how much aliens can learn about your home planet by examining seemingly innocent details of the ship. For instance, they can learn clues to your homeworld star's spectral class by analyzing the frequencies emitted by the ship's lamps and track lighting. And the crew can be tortured for information, especially the astrogators (to get them to cough up your homeworld's coordinates) .