Designing an escape capsule for a novel

[TheWhiteZombie]

I'm not sure if this is the correct place, or if NasaSpaceFlight allows these sort of threads, but you are the best space geeks I know and if any of you are willing, I would love your input.

I am attempting to design an escape pod for a starship (science fiction, figure at least 200 years in the future). I tried many simple designs, many one man "pods", a few life boat muti-crew vessels, but none really seemed to fit. This had to be a system that would evacuate the entire crew of a navy frigate, except that this frigate can travel between star systems, and it's in space. The crew could have to survive months (or years) before rescue depending on where they are forced to evacuate. (Definitely no 5 minute ftl jumps. Possibly no FTL at all, TBD). But there is limited space available on a starship (especially a warship).

My solution was to have 5 man pods, with "coffins" (to be changed) for the crew to slide into, with the outer layers being expandable walls, to allow a tolerable living space. For most people, the concept would be enough to write the novel, but I am very detail oriented, and even if only a tenth of the information will end up in ink on the page, I need to know what I am writing about. I need to understand the setting. I've sketched the basics here, please excuse the imperial units. I'd almost finished before I caught myself. Heavily inspired by bigelow, and his modular station.

Capsule is cylindrical, storage in the center for essentials along with short term life support and ISRU (misspelled in sketch). 5 2'x1 1/4' coffins for crew, with everything possible packed in around them. Then the collapsed walls, and then a metal cover on the outside to allow smooth rapid ejection from station.

1.5 feet designated for hatch on front, 6 feet for crew coffins, another 1.5 for the second hatch, then three feet for communal equipment - shared essentials that aren't needed for every capsule. (like a group of hikers, one gets the tent, another the stove, and another the pot and pan). I.E. long term life support units, water recycling, long distance communication unit, etc. About half would be extra supplies, and the outer canister for these would be used to extend the docking hatch (to space them out from the mating blocks.)

Mating blocks are launched packed with additional supplies, but no crew and ejected when the evacuation order is given.

The ship these specific capsules are designed for is a frigate with a compliment of 200 crew. With 5 men each, the entire ship would require 40 capsules.

The illustrations are limited to basic drafting, because I am completely useless drawing anything without a compass or ruler. I have most of the details worked out, coffin frames used for storage once the capsule is expanded, the zero g "beds" are the strapped & padded harness of the coffin. All crew has pressure suits.

I am probably over thinking all of this for my novel, but the modular station is the setting for a sizable section at the start of my book. There is an additional maintenance/utility craft for assisted assembly.

Please note, the cross section side view is not an actual cross section, just the best visualization I could do. The pod would not be symmetrical at a cross section because there are 5 coffins.

I present to you, the Ark(Or EXITS, Emergency eXtraction Inflatable Temporary Station)- torn between the two.

[A_M_Swallow]

If the pods cannot fly to the destination then they will have to have long range communications equipment so the rescuers can find them.

[TheWhiteZombie]

If the pods cannot fly to the destination then they will have to have long range communications equipment so the rescuers can find them.

Sorry, I just realized how little information I actually included in my post. That three feet at the end of the capsule is communal equipment. I'm assuming 200 years from now a three foot thick cylinder with an 8 foot diameter would be enough to pack in a powerful comm suite or beacon.

Initial post updated with much more detailed information on capsule.

[RonM]

Do you need the escape capsule for the story? Is it a SF lifeboat story? If not, then it would make more sense to stay with the ship. The crew really isn't going to be going anywhere and the ship could have all the survival supplies needed for the emergency.

Why is the crew so large? Troops or colonists? A SF ship should be highly automated, requiring a small crew.

If you haven't already checked out the Atomic Rockets website, its worth looking into. Good resource for writers.

http://www.projectrho.com/public_html/rocket/

[TheWhiteZombie]

Do you need the escape capsule for the story? Is it a SF lifeboat story? If not, then it would make more sense to stay with the ship. The crew really isn't going to be going anywhere and the ship could have all the survival supplies needed for the emergency.

Why is the crew so large? Troops or colonists? A SF ship should be highly automated, requiring a small crew.

If you haven't already checked out the Atomic Rockets website, its worth looking into. Good resource for writers.

http://www.projectrho.com/public_html/rocket/

It is something of a castaway story, in space of course. Ship is rendered completely uninhabitable (atmosphere vented and swiss cheese) and only a handful of the capsules will actually survive. The MC of the story is an engineer, they are stranded in an asteroid belt in a backwater, lawless system. They can't activate their distress beacons for fear of attracting the attention of pirates, raiders, or reavers (the cause of their ship's destruction) and have to wait and hope that their colony sends a rescue crew to the location where the frigate went down (last broadcast of the ships S.O.S. beacon) and hope they search long enough to find them. They will find what is left of a completely ruined alien space station, and between their temporary modular station (which is missing some essential parts, some communal gear and their spares didn't survive.) and this ruined hulk, they will struggle to survive.

The 20-ish survivors have 4-5 surviving capsules, the ruins of three ships, a derelict alien station, a single engineering/utility pod, and all the asteroids their little hearts desire.

I am using a sci-fi style asteroid field, with a much higher density than occurs in reality. Think star trek/star wars, asteroids everywhere.

Not the best setting, but something I've always wanted to write.

As for the crew, I figure:
20 bodies for cic/command deck, three shifts = 60
20 engineers (fighter/shuttle bay, armory, utility drone service/control, life support, engines, etc.) x 3 = 60
4 pilots for fighter craft, backup pilots = 8
30 marines, for boarding actions both offensive and defensive.
~22 for everything else. Chefs, plumber, IT, etc.

seems fairly reasonable. It's a fairly large ship.

[GreenShrike]

Off-hand notes -- feel free to disregard, hand-wave or magi-tech away.

Have you determined a maximum usage duration for these capsules? "Months (or years)" is a very long time to be surviving without some sort of resupply. Is there any reason the survivors need to be conscious the entire time? Cryogenic suspension/induced coma/hyper-sleep can cut down on required supplies if very long durations are required, and the tech is available.

I see "food/water" listed on the diagram, but while water can be recycled pretty efficiently -- though cleaning filters may be interesting after a while -- food sort of sets a hard limit on crew survival, unless you have some way to grow/manufacture more out of waste materials (there a toilet somewhere?) and an energy input. There doesn't seem to be a lot of volume for hydroponics.

Have you done the math on those solar panels? Even assuming magical 100% efficiency, you're going to be limited by panel area and by distance from the star (e.g. Mars gets around half the sunlight Earth does, and the asteroid belt even less). How are the panels deployed? The skin of the capsule won't have much area facing the sun, but extendable arms presumably increase the capsule's detection surface and in an SF very high density asteroid belt, drastically increase the required volume of clear space needed to avoid collisions. Your station of capsules might run into panel deployment issues as well -- the ISS' arrays, for example, shade the arrays on the Russian segment, which is why the Russian panels are folded away.

Perhaps an item of communal equipment is a micro-fusion reactor or something?

You list air tanks, but as every reader of The Martian is well aware, it's not lack of oxygen that'll kill you -- it's excess CO2. Do you rely on a scrubber to remove it, or does the ISRU gear convert it into something more useful?

Medical facilities. Some of the crew are likely to be injured after abandoning ship. What facilities to the capsules have for treating minor and major wounds? Do the coffins have auto-docs? Or do the capsules just have a first-aid kit, and an auto-doc is communal equipment?

Hauling in another ISS example, their 3D printer just printed a tool. A manufacturing array plus input stock might be smaller than pre-made tools and supplies, some of which may not be required in a given set of circumstances. For example, your 3-item crate has packed a widget, gizmo and a thingy, but you have no use for a thingy and could really use a pair of gizmos.

Don't military escape craft usually have an arms locker for basic defense?

Oh -- again with the ISS. What are you doing about waste heat? Radiators are a fairly essential part of current space craft.

What facilities are present for command and control? Other computing needs? Sensors? Radar masts? Other antennae?

What happens when a frigate is destroyed while in low planetary orbit? How do the capsules survive to reach the ground? Or do they have sufficient propellant to boost themselves out of any atmosphere dragging them down? If so, do they dare use it in the middle of a battle?

What happens when the hull is damaged by battle? What redundancies/auto-repair/work-arounds are in place to help ensure the survival of the crew when the capsule isn't outright destroyed but only lightly damaged? Moderately damaged? Heavily damaged?

I'll note that 200 crew with 40 capsules shows a lack of redundancy when you're abandoning ship because it's been wrecked. What if 75% of the crew survives but only half the capsules do? Perhaps have a capsule capacity of 125% of a standard complement, to account for battle damage, as well as passengers or other extra personnel?

You mentioned pilots and fighter craft. Do the capsules have any sort of S&R capability for picking up ejected pilots?  Do the pilots just eject in their seat+suit, or does an escape pod come off the fighter? If the latter, how do the capsules and fighter pods play together?

I don't see any thruster ports. Propellant-less propulsion?

That's it for now, I guess. To sum up: air and water, power to keep them clean and usable, long term food, medical, heat management, repair facilities, landing capability.

[TheWhiteZombie]

Off-hand notes -- feel free to disregard, hand-wave or magi-tech away.

That's it for now, I guess. To sum up: air and water, power to keep them clean and usable, long term food, medical, heat management, repair facilities, landing capability.

Thank you! That is exactly what I was looking for! I will do my best to answer.

Max duration is going to be 6-12 months without resupply. That depends entirely on how long I figure the food can last, however I can't find any solid metric of how many days of food fit in a certain volume. All the info I have found has been mass focused. The crew does need to be conscious unfortunately, as my story would be pretty boring otherwise.

Water is definitely recycled, and as you say food is really going to be the issue. I had considered having hydroponics gear in one of the communal capsules, however the volume is limited. Even dedicating an entire capsule wouldn't be anywhere near enough. There is a toilet, built into the central column, however I am not sure a bio resequencer is really the solution I would want to go with. It's a bit of a cop out when it comes to a castaway survival story, so it either won't be a viable technology or the capsule with that bit of gear won't survive the battle. Waste would either be disposed of, or stored. TBD

There are 10 solar panels (stored 2 deep) each ~2 feet by 6 feet. That is 120sq feet, as for power consumption I don't even know where to begin calculating the power requirements of futuristic equipment and computers, so from a story telling perspective let's say its not enough to live comfortably, but enough to power essential systems at minimum required capacity. That plus more efficient future tech for the internal power usage I don't think this is too unreasonable. My plan, was that the station would be oriented so that there was a "top" where even though they can build the station out in 3d, one side, and the largest collection of capsules, would be completely flat and facing the sun. The first panel would latch on to a mount on the middle (the equator?) of the expandable module, and the rest would be plug and play into the sides after that, latching on when they meet the jutting edge of the next module. There would be a generator/reactor in the communal gear on one capsule, I haven't pegged down the type of energy generation. (This won't survive either. Can't make it too easy on them.)

Air tanks are more to inflate the walls, and fill the volume of the expanded module, as well as re-pressurize in the event of a rupture once it has been sealed. (I use air to refer to the cocktail of gases required for our bodies, it is not pure oxygen.) Oxygen is very much recycled, co2 is scrubbed, not exactly sure what could be done with it.

Each pod has a first aid kit. The magic miracle tool is going to be a biofoam, which is really just a foam plug. Stops bleeding (mostly), but is not a long term solution. Full medical suite is communal gear. (It will survive, I'm not that evil.) Coffins are literally padded metal boxes, with an ambulance style restraint bed. There is a display screen in front of their faces, a closed ventilation system (linked up the capsule life support, but not each-other.) It would definitely be a design flaw, but the first aid kit won't be accessible until the capsule inflates.

A fabricator (sci-fi, fancy 3d printer) will be on each utility pod.

I hadn't thought about an arms locker (thank you!). I think the most space conservative way would be a pair of pistols per craft. (super sci-fi pistols of course)

For heat, I actually need to ask. Do you mean a radiator inside to generate heat or one outside to cool off? If you think they need more heat, I'm going to say part of the life support system. If you think it would be too warm, I'm going to say that these advanced technologies are more energy efficient than our current options, and there is much less waste. I hope that's not too much magitech.

Sensors, Radar, and antennae of some sort would all be in the com suite (more communal gear. If I hadn't spent so much time backpacking, I would be a total loss trying to fit all of this onto each and every ship.) With advanced computing, any capsule is capable of being the command module. Extra screens could easily be brought over from other pods (if necessary), but really, 200 years from now computing power should hopefully be a solved issue. I don't plan for it to take up any notable space, and the screens would be no thicker than a centimeter. (also considering holographic displays, but I like the idea of tactile interfaces.)

What happens when a frigate is destroyed while in low planetary orbit? How do the capsules survive to reach the ground? Or do they have sufficient propellant to boost themselves out of any atmosphere dragging them down? If so, do they dare use it in the middle of a battle?

This is the big problem of the day, and another thing I hadn't even considered. Thank you for bringing it up! I had planned for small Ion engines,(that seems to be the sci-fi favorite) I'll draw up a few more diagrams for engine placement. However I really only have two choices here that I can see. Either the small engines are powerful enough to boost away, or the frigate was never designed for low orbit or atmospheric use. I.E. built in high orbit (star trek) and intended to stay up there. If you have any other ideas I would love to hear them, but for now I'm leaning towards the second option.

The capsules will not have auto-repair functions, but as long as the capsule still has power, and at least two of the 5 air tanks, the capsule could still be inflated via sectioned parts of the wall (inflated like beam, where the walls inflate rather than forcing it open via internal pressure like a balloon.) From there, the holes could be patched. If they lose power, there would be a secondary batter on the opposite side of the capsule, and some redundancy in computing power distributed throughout the central column. Every crewman is supposed to have a pressure suit on before entering the capsule, so loss of atmosphere would not be fatal, oxygen would be supplied to helmets via tube connections to life support. For severely damaged, they would have to hope one of the utility craft survived.

Capsule redundancy is a VERY good point and yet another I hadn't thought of. I have no hard plans laid out for the frigate so we can just up the number to 50 and I can deal with it later.

S&R would be primarily the job of the utility craft, however as long as they have coms, engines, and power, they could handle S&R, just very slowly and delicately. The craft is deigned to be able to have it's atmosphere vented and replenished, I actually planned for one capsule to be designated as an "airlock", any capsule would be able to do this. So it's really just a matter of opening the hatch and letting them in. once they are nearby. (Not ideal but that would be the best contingency I could imagine in the event no utility pods survive evacuation without a major overhaul.)

Engines are built into the frame of the communal storage, small thrusters on the rim of the docking port. I'll sketch it out and post.

Thank you so much. Really. About half of that just came up as I was trying to answer your questions, which is why I needed external input. I hope I didn't magitech everything away too much!

[TheWhiteZombie]

Sorry, the solar panel configuration, and the capsule layout is not to scale at all. Just a quick sketch to show how it would work, and there are many more capsules below that first layer. (Relative up is towards the sun, down is away from the sun. Since the capsules would have to be oriented towards the sun for the panels, this makes sense.)

And sorry for the lack of detail on the engines and thrusters. I honestly don't have the technical knowledge to design even a simple engine, I am really just aiming for knowing what is there, where it is, and if it really fits in the size of the capsule I've designed. I think of it as a 3d checklist, making sure I have all the bases covered. Plus, I am a writer, not an artist. I hope these convey enough information to be useful.

Something I didn't answer above, or mention, is that the temporary station is not designed for use in an asteroid field. At all. Call it a design flaw, or oversight, it is a major plot point in the story, and completely intentional. They engines and thrusters are perfectly capable of maneuvering enough to get into configuration, and make minor adjustments with plenty to spare, but they do not have the ability to escape the asteroid field.

[A_M_Swallow]

It is possible to have a main engine that only flies in a straight line - many sea ships do. They use a rudder to change course. The spaceship equivalent are Roll Control System (RCS) thrusters. A good set of RCS thrusters allows a spaceship to turn in any direction. They are tiny rocket engines. Damage the RCS or their fuel tank and the spacecraft will be unable to avoid the asteroids, although the landing would also be difficult.

[TheWhiteZombie]

It is possible to have a main engine that only flies in a straight line - many sea ships do. They use a rudder to change course. The spaceship equivalent are Roll Control System (RCS) thrusters. A good set of RCS thrusters allows a spaceship to turn in any direction. They are tiny rocket engines. Damage the RCS or their fuel tank and the spacecraft will be unable to avoid the asteroids, although the landing would also be difficult.

I definitely agree! The idea is that there are four small fixed engines around edge of the cargo rack (new name for the "communal storage" I've been referring to this whole time.) on the back, with 16 thrusters, 8 each on the front and the rear for turning on every axis I can think of.

[liam]

That depends entirely on how long I figure the food can last, however I can't find any solid metric of how many days of food fit in a certain volume. All the info I have found has been mass focused.

Hi, this sounds like an interesting story.  Some data on emergency rations, both short and long terms: in the short term there are pastes and ration 'biscuits', the latter being in quotes as this has quite different meanings in different English speaking countries. Emergency ration biscuits are similar to unsweetened shortbread (sweet shortbread is deliquescent and absorbs moisture, making it unsuitable for marine rations, the most typical use); they are usually vitamin enhanced. These contain 0% of daily water requirements. The attached picture shows a typical example, at 7x6x3cm for 128cm3 at 500g they are 3.52g/cubic cm. These are able to keep a healthy adult OK on a liferaft for 3 days (given relative inactive levels on a small raft, non artic weather, which I assume to be similar to your survival module; with possibly a lower energy requirement if you have no AG). They will also keep an adult alive for 2-3 months at a level of 1 box per 6 days, but at significant fat and muscle loss. NB neither food requirement assumption would be true if any of your surviving crew or marines are staying in fighting condition against local pirates etc.

Pastes are more typical from eastern European emergency rations, many early cosmonauts used a variant such as borscht tubes.  These can be meat or vegetable pastes, and in some cases can be mixed with water to make a thick soup or stew, dependant on added water level (although AFAIK this is gravity well limited,  haven't read any thing about this being done on Mir or Salyuz missions. The only tube I have (meat paste) is 2.8g/cm3 @ 21% water content, but as a single data point I can't swear how representative this is. The paste has a three year life span, and the biscuits five.

For long term rations in a space environment where near 100% water recycling is in place, freeze dried (emergency) rations would provide maximum efficiency. ('Wet rations', similar to the meals we eat each day, result in a lot of additional moisture dispelled into the surrounding atmosphere [sweat, urine, faeces etc], either this needs ejected or stored from the environment.)  Typical state of the art freeze dried rations are from suppliers such as mountain house. Mass is a little difficult to tell, individual pouches are 1.6 to 2.1 g/cm3, but there is a lot of packaging in individual rations.  The #10 tins, while offering the quoted 7-11 meals often have a surprising amount of free space at the top of the tin, not sure if this is required or marketing. Count on just over 2g/cm3 if it isn't. Feeze dried foods have a typical lifespan of 20 or 25 years at this time. (EDIT: realised I'd given you density but no mass requirement; standard meal (inc individual foil pouch at circa 5g) is 108g for c. 550kCal, active meal is 166g for c 750kCal, slightly dependant on meal type. Veggie meals are different, e.g.186g for 650kCal veggies and rice.)

Freeze dried breakfasts are ok if you need to serve hot meals to keep your crew warm, otherwise something like muesli would be more mass efficient. Say 45g inc powdered milk for 170kCal at 2.4g/cm3 for the muesli. Dried fruit would also be a mass efficient snack food, with the exception of melons this is fairly common and would allow a range of flavours.

On this note it's worth adding to make sure there is sufficient range of foods for long term survival. Survivors can suffer from "food ennui", where there is enough food, but either bland or insufficient choice means survivors let themselves starve in the presence of sufficient food. Most military forces recommend that troops use prepacked rations for 21 days max as a result; US forces have a choice of 24 main meals, German 20, Canadian 22, UK 20 (although halal/kosher/sikh/Hindu are limited to 6 each), French 14. Typically there are only 4-6 breakfasts that repeat with the entrees. For volume calcs a French 24h MRE is 3200kCal in 29.4X14.9X6.3cm @ 1.5kg for 3.46 g/cm3, but there's a fair amount of cardboard packaging in that, which team rations would reduce. PS while French and Chilean MRE used to contain a small wine bottle,  this practice is long gone (shame!).

Air tanks are more to inflate the walls, and fill the volume of the expanded module, as well as re-pressurize in the event of a rupture once it has been sealed. (I use air to refer to the cocktail of gases required for our bodies, it is not pure oxygen.) Oxygen is very much recycled, co2 is scrubbed, not exactly sure what could be done with it.

On this one, unless state of the art changes significantly, the limiting factor on ELCSS is indeed CO2 scrubbing. I admit to knowing little apart from what i've read here on space station ECLSS, space systems efficiencies may be way in advance of underwater systems (and probably are, we throw away some gas on ascent to relieve pressure, and use a little more as buoyancy aid and drysuit pressure comfort) but the following may give some light to the long term scale of CO2 scrubbing.

The values below are for an Inspiration XPD rebreather; 1x3L cylinder @ 200 bar with O2, 1x3L cylinder with trimix.  Effectively the N2 and Helium would be reused  (bar interior leakage, He is slippy stuff). Practically that is (just under) 10h for an averagely fit male. However, the CO2 scrubber, Sofnolime, must be replaced after 3h exposure to CO2 at 1.6 bar (atmosphere). In a 1 bar environment that would give you five hours (half the O2 available duration); in this time the person would have consumed 0.3 kg of O2 but 2.45kg of Sofnolime in that period.

Admittedly there are more efficient if expensive CO2 scrubbers (some of which are too dangerous to be used underwater, but are possibly ok in a space station), but bar some technological leap to separate CO2 into O2 and solid C there is either a need for lots of CO2 scrubber or an O2 supply to allow CO2 venting (in the case of venting,  you would need to count in c 550L per adult male per day at 1.43g/L, excluding storage mass for 0.79kg/person/day. PM me if you want numbers on storage cylinder mass). Anyway, either option could add significantly to your module's storage requirements.

Wishing you all the best in your writing
Liam

[TheWhiteZombie]

Hi, this sounds like an interesting story.  Some data on emergency rations, both short and long terms...

Another truly wonderful post! Thank you!

The #10 tins, while offering the quoted 7-11 meals often have a surprising amount of free space at the top of the tin, not sure if this is required or marketing. Count on just over 2g/cm3 if it isn't. Feeze dried foods have a typical lifespan of 20 or 25 years at this time. (EDIT: realised I'd given you density but no mass requirement; standard meal (inc individual foil pouch at circa 5g) is 108g for c. 550kCal, active meal is 166g for c 750kCal, slightly dependant on meal type. Veggie meals are different, e.g.186g for 650kCal veggies and rice.)

You make a very compelling argument for freeze dried, and the metrics you provided were exactly what I needed! I cheated a bit, and for a quick assessment I used the standard meal @108g for one meal, with 2g/cm3. I rounded (I will do proper math later I promise!) the 108 to 100, so 100g @ 2g/cm3 leaves us with one meal using up 50cm3.

A quick calculation revealed I have 3.6 m3, or 3,600,000 cm3. This is entirely in the storage between the coffins and the inflatable walls. I designated a third of that volume for water, leaving 2,400,000 cm3 for food... which leaves me 48,000 meals... or a 3,200 day supply for five people. Which is as wonderful for the castaways, as it is absolutely awful for the purposes of my story.

So I have a few options, I can think of more stuff to cram in there to reduce food storage space, (the mating cubes will not be launched packed with food now!), I can redesign my whole capsule to be smaller (even though it fits 5 perfectly as is, and I thought it would be too small already)... Or I can leave the intended food quantities as is, because that might be a reasonable amount of food for an interstellar ship to have while they wait for another ship to come rescue them, and introduce story driven variables so the design of the vessel isn't compromised by my sadistic intentions.

I.E. spoiled food. The frigate is planned to be an aged 30-40 year old military vessel, bought by an independent frontier colony at a steep discount, so maybe they forgot to check the emergency rations? Maybe they board an attacking pirate ship and find a cargo hull full of slaves, lots of untrained mouths to feed. Maybe there is a malfunction and the pod they are storing their rations in has a critical failure. Anyway... that is a writing issue.

This is of course assuming my math was correct. And that gives me plenty of room to low ball the amount of food that could be stored so I can ensure they would have varied meals without crunching numbers frantically.

On this one, unless state of the art changes significantly, the limiting factor on ELCSS is indeed CO2 scrubbing. I admit to knowing little apart from what i've read here on space station ECLSS, space systems efficiencies may be way in advance of underwater systems (and probably are, we throw away some gas on ascent to relieve pressure, and use a little more as buoyancy aid and drysuit pressure comfort) but the following may give some light to the long term scale of CO2 scrubbing.

For the air, I have hit an equally large spatial jackpot, with over 3 m3 dedicated to air storage. Splitting that in half would leave plenty of room for co2 scrubbing chemicals. Between inflating the pods, and the fact they are in an asteroid field I think I will have plenty of opportunities to cause their oxygen storage to dwindle without making too much of a fuss. I had no idea just how huge cubic meters were... Which is really stupid because I used to help my old boss order cubic yards of concrete all the time. Just seems a bit different when it's life saving food rather than some sludge you have to level and smooth.

Really, thank you again! And feel free to check my math, or throw in other things!

[Wicky]

"Maybe they board an attacking pirate ship and find a cargo hull full of slaves, lots of untrained mouths to feed."

or rather supplementary rations ... http://www.telegraph.co.uk/culture/books/3664711/Cannibalism-on-the-high-seas.html

http://www.livescience.com/51614-doomed-franklin-expedition-cannibalism.html

http://www.thesundaytimes.co.uk/sto/news/uk_news/article236426.ece

“There is no cannibalism in the British Navy, absolutely none, and when I say none, I mean there is a certain amount.” Graham Chapman > Expedition to Lake Pahoe (3.09) https://www.youtube.com/watch?v=3DlN4Sh06po?t=3m9s

[Wicky]

“Six guys living in a space about the size of a double bed, in which you must attempt to sleep, navigate, go to the toilet in a bucket, you’re sick on one another, it’s wet, it’s cold… it’s… pretty desperate.”

https://mpora.com/mountaineering-expeditions/death-despair-cannibalism-tim-jarvis-recreated-mawson-shackletons-ill-fated-antarctic-expeditions-find-really-happened

[liam]

48,000 meals... or a 3,200 day supply for five people. Which is as wonderful for the castaways, as it is absolutely awful for the purposes of my story.

Absolutely.  I think it might haver been Louis McMaster Bujold who said in an interview (I paraphrase) 'I think up the worst that could happen to my character, then do that to them!'

If I may offer some additional thoughts on your numbers, things actually are a fair bit more difficult for your castaways than the raw figures show. 

Using the 3-3-3 survival rule of thumb (3 mins no oxygen, 3 days no water, 3 weeks no food in an otherwise benign environment with no toxic atmosphere) the oxygen and water are much bigger concerns.

Oxygen
Based on the consumption of O2, there are probably four ways to keep on providing in this type of situation
i) open circuit, dump the CO2 overboard and top with fresh O2
ii) closed circuit, chemical extraction
iii) closed circuit, magic life support system with no consumables
iv) external resupply AKA salvage, looting or IRSU

Taking the first, full open circuit general rule of thumb is 1L of breathable gas per person per minute, at moderate exercise in a 21%O2 in a 1 Bar environment (for those using imperial measurements, 1 Bar is approx. 1 atmosphere if you're not being scientific).  Either all of this is dumped after one breath (very wasteful but mechanically efficient, requires 1,200 L per person per day of gas), or you dribble some offboard and recirculate the balance which is more efficient for gas supply, but needs extra monitoring to manage an acceptable CO2 level (a fair estimate would be that 550L of free gas, oxygen rich in storage).

Modern gas store cylinders for scuba and firefighting use 232Bar or occasionally 300Bar cylinders, storage slightly higher at 350Bar.  State of the art in future might give you exoticum materials, but the mass of the cylinder scales with pressure.  Carbon fibre is lighter than steel or Aluminium, but it's a pain to test integrity.  On board diving ships they are delivered as 'quads', typically sets of 4x4 cylinders bolted together in an assembly weighing c1200kg and sized just over 1x1x2M in dimension. 
An example: http://www.divexglobal.com/capabilities/commercial-diving/compressors-panels-and-umbilicals/show/hp-storage-banks-quad-system
This would give 16x44.5x350 = 249kL, which would last your crew 34 or 90 days in a no-accidental-losses setup.  This is strictly a days/weeks to rescue configuration, even if you went for a more efficient cylinder volume (at the cost of redundancy).

Second config, closed chemical scrub.  Taking Sofnolime again, as I'm most familiar with it.  Supply is in 25L volume pails, with 20Kg of product.  There's only a couple of inches of air in the top of a new pail, so density is probably close to 1kg/L.  The reason for this is that it comes as small chalky looking pebbles, and can't be crushed into powder as you need channels for the gas to flow through.  Personal rebreathers get through that 20Kg in 24 duty hours, so the numbers become ridiculous for long term use.  However, I've met (crazy) people who use it for several times the duty cycle, but you take a gamble on when it will reach max CO2 absorption capacity; you might get significant economies of scale if you have a monitored life support system that lets you use it to the last gasp.  However, I offer these numbers as possibly a constraint on how many EVA ops you can do, these will likely be one of open circuit or chemical extraction.  (NB using a CO2 scrubber is exothermic, pain in a spacesuit to radiate, but if your capsules are in a cold soak similar to a diving bell then it's very pleasant to be supplied breathing gas at around 25 Centigrade.)

Third config, Arthur C Clarke magic territory.  Some device for extracting the carbon from CO2.  However this is still likely to need significant energy. Take the lower figure of 0.79Kg of O2 per day per person to be reconverted back from CO2, in a 100% efficient setup you would still need to find the Gibbs free energy. I show the calc below so you can put your own assumptions:
    ~Gibbs energy of CO2 => C + O2 = 395 kJ/mole
    0.79Kg : 790g @ 32g per mole of O2 = 24.7Mole
    24.7*395 = 9.75MJ per person per day
    9.75MJ: 9.75/3.6 = 2.7 kWh per person per day
So need to find 13.5 kWh + inefficiencies per module per day, that's a hefty requirement on your solar capacity.

Lastly, an external resupply.  There's plenty of IRSU articles about, so I won't recap asteroid mining.  It's hard to imagine that with three wrecked vessels in your story that life support isn't multiply redundant and nothing can be scavaged.  It's amazing what can be found usable on a sea going large steel hulled vessel after fire or even a few weeks of sinking.  Final option is of course lifting from hostiles, depending if you want any (more) daring scenes.

It's late my time, so if any of this is of use (or interest to any other reader) just let me know and I'll continue with water, food, power and external-SAR later in the week.  (And how freeze dried generates so many issues for anyone's starving storyline in well prepped survival stories, so I'll consider how you could end up with unusable stores.)

Regards
Liam

EDIT: typo

[TheWhiteZombie]

First off, Liam, you are amazing.

Now I will start off with the solutions I came up to counter your overly helpful dehydrated food. Because I actually have some ideas for that.

A: Officers stealing the emergency rations during intersystem transit because of the hard rationing to make supplies last for +10 years.
B: Enlisted crewmen doing the same, different dynamic for anger placement.
C: Stolen & smuggled off ship to trade on the black market with a starving colony
D: Substandard low-bid emergency rations, most of which have expired or the packing has contaminated it

It might be cruel to make them hungry, but if everything goes smoothly it's an awfully boring story. That is the best I can think of for the moment without intentionally sabotaging the design of the capsule. Now for tech problems.

As for the oxygen issue, I had no idea it was that bad. 20L/day per person for scrubbing is an impossible metric. I had always imagined food would be the problem, and had assumed that air would be simple.

Using 20l per person, per day, I've figured I can get 20 days out of 3 m3 (I will cut the food stores in half for 1.2 m3 of oxygen storage for inflation and ambient air.

Yes, external resupply will be possible in this situation, and something that will be actively explored, but the design has to be reasonable if the ship fails in the dead space between stars where the ships reactor blows and the frigate is atomized. So I need something that will work for about two years, and that doesn't seem possible with current tech. All is not lost however! A 20 day supply is rather reasonable for an individual capsule, with them being reliant on the communal life support systems in the cargo pods.

For the purposes of the story, and assuming humanity advances somewhat in the next 200 years I will probably go for a mix of chemical scrub and technomagic in the life support systems. Probably using half the power requirement you came up with in exchange for consumable chemicals. Lets say the chemicals are extremely toxic which is why they wouldn't be used in the individual pod systems.

I hate to use technomagic for something as essential as oxygen supply, however I can't think of a way around it. Short of making the escape capsules exponentially larger. Thank you again for the solid volume metrics! Even if I run into problems with my design and have to fudge things, it's better than not knowing they are there!

[A_M_Swallow]

On Earth the normal way CO₂ is converted back into oxygen is via photosynthesis in plants. Some bacteria and plankton can also do this. Spaceships do not use this method because too much area is needed.

The fictional Babylon 5 spacestation used this technique but it was 5 miles long.

[TheWhiteZombie]

On Earth the normal way CO₂ is converted back into oxygen is via photosynthesis in plants. Some bacteria and plankton can also do this. Spaceships do not use this method because too much area is needed.

The fictional Babylon 5 spacestation used this technique but it was 5 miles long.

I understood the biological method, I just had no idea how horribly inefficient our artificial ones were. I simply assumed that with submarines and the ISS we had something better than electrolysis or something requiring 20kg of a consumable per person per day. I've read about the methods before, but having never tried putting the numbers to use, they were just interesting facts. Trying to use them on a spatial budget really puts it in perspective for me. Even if the spatial budget is self imposed, and entirely based on the idea that every escape pod is essentially wasted volume and mass on the frigate so they would have to be as compact as possible.

[punder]

My intuition says biological humans will not be warfighting, especially in space, two centuries from now. But that's the big problem with SF these days, isn't it? You have to write stories that readers (i.e., paying customers) can relate to. They can't relate to godlike AIs. So... To hell with my intuition. 

NASA is already studying hibernation technologies for interplanetary flight. So a future space lifeboat would, very likely, employ hibernation for biological humans. Far less consumables mass, no psychological or group-dynamics considerations. They would only awaken upon reaching an environment sufficiently resource-rich to sustain them indefinitely (or long enough for definitive rescue by friendly forces).

On the other hand, that really cuts into the drama, doesn't it?!

I really admire and respect those willing to hang their butts over the edge for science fiction. Good luck to you, and I hope to read this thing someday.

[Doesitfloat]

Sounds like a good read

Water---
By my recollection science fictions stories tend to treat water as a scarce commodity however, science is showing exactly the opposite. Water/ice is everywhere in asteroids, planets, and planets rings.  Most/all of the water is i the form of ice. Uses for abundant Ice:
1) Melt and filter for drinking water- Raw ice is probably going to have cosmic minerals/dust that can be abrasive or just taste bad. While I doubt a bacterial life form can survive in space ice a spore can serve as a vector for a nasty organism or a helpful one.
2)Propulsion-(High thrust) Heat water to high temp and shoot out a nozzle like a chemical booster rocket.
3) Refine Water for oxygen.
4) Refine water for Hydrogen- Hydrogen can be used for fusion reactor.
5) Refine water for Hydrogen- Propulsion (Low thrust high efficiency)- Future ion engines can use Hydrogen or noble gasses for high efficiency engines.
6) Hot Tubs