[Spaceships] Total life support

[Agemegos]

The rules for total life support on p.17 of GURPS Spaceships are a touch on the sketchy side. I suppose that is probably in keeping with Spaceships's "nearest half-order of magnitude" approach, but there are some anomalies, and frankly, the rules seem a little harsh.

Accommodations include an air, water, and heat/cooling supply for as many people as they can accommodate.

Providing a food supply in addition requires either

• a replicator system (requires TL12^);
• an open space given over to farming or gardening; or
• doubling of the mass/size of the accommodations

A single replicator system is capable of producing any amount of food required by as many people as are likely to be on a ship. In theory that could be eighteen systems of bunkrooms accommodating 72 people times the number of cabins per habitat at the ship's scale. That works out to about 8 people per ton of replicator, or about 65 people per cabin of replicator. Given that a ship designed to carry people is more likely meant to have 7 habitat systems than 18, a conservative figure might be more like 30 people per cabin of replicator.

An SM+10 replicator (can produce 1,200 lb per day of anything, which is enough fresh food to feed 240 people. That's a bit disappointing. Noting that 1.4 lb of freeze-dried food will suffice, we might suppose that the replicator can add water trivially and that the SM+10 replicator can feed 800 people. On that basis a ton of replicator could feed only 1.6 people. We must suppose that replicators are especially efficient at making food, particularly as it is nowhere stated that the replicators are flat out making food.

An open space given over to gardening is, by the RAW, adequate for an entire ship-full of people in bunks. On that basis 1/4 of an acre of gardens (1 SM+10 open space) would be necessary to feed 60 people (1 SM+10 habitat system of single-occupancy luxury cabins), but sufficient to feed perhaps 1,680 (six SM+10 habitat systems of bunkrooms) or even more. That is, to put it mildly, dizzyingly optimistic. I'm not strong on gardening, but I don't think you can support more than about four people per acre of conventional intensive horticulture. Make a generous allowance for a controlled environment, intensive hydroponics, high-tech genetically-engineered crops, absence of diseases and pests etc., and I think you would be looking at at least one area to feed each person. That's 100 tons of garden per person.

Finally, "total life support" halves the number of people who can be accommodated in a habitat system. That implies that the equipment to produce a person's food masses 2 tons if the person is living in a bunkroom, or 8 tons if the person is living in a single-occupancy luxury cabin. A cabin of life-support equipment will feed one to four people.


Consulting the indispensible Nyrath's Atomic Rocket site, I find that a life-support system using algae to produce oxygen and food seems likely to mass somewhere between 250 kg per person and 56 kg per person. The algae don't sound very appetising, but there are kitchen facilities included in the habitats, and yeast cultures and fauxflesh will presumably be on the same order of magnitude for productivity.

I propose, therefore, that a cabin (8 tons) of life support machinery ought to produce enough food for thirty people at TL8, seventy people at TL9, and 150 people at TL10, while at TL11+ providing food should be a trivial byproduct of providing water and oxygen.

[nick012000]

Originally Posted by Brett

An open space given over to gardening is, by the RAW, adequate for an entire ship-full of people in bunks. On that basis 1/4 of an acre of gardens (1 SM+10 open space) would be necessary to feed 60 people (1 SM+10 habitat system of single-occupancy luxury cabins), but sufficient to feed perhaps 1,680 (six SM+10 habitat systems of bunkrooms) or even more. That is, to put it mildly, dizzyingly optimistic. I'm not strong on gardening, but I don't think you can support more than about four people per acre of conventional intensive horticulture. Make a generous allowance for a controlled environment, intensive hydroponics, high-tech genetically-engineered crops, absence of diseases and pests etc., and I think you would be looking at at least one area to feed each person. That's 100 tons of garden per person.

Maybe there's more than one level of horticulture, stacked on top of one another?

[Fish]

I was looking over the maximum capacity of spaceships just last night, and even taking into account the need for engines, fuel tanks, power plants and so forth, I came up with some seemingly ridiculously high populations per ship.

The problem with the mathematics, I think, is that a garden yield scales by the square, and ship capacity scales by the cube. Unless a way could be found to make garden yields scale in the same way — stacked, as nick says — we'll need a new model.

One thing to take into account, perhaps, is that accommodation of humans is far from 100% efficient. Although you could technically fit a large ship with wall-to-wall cabins, in reality you would need a certain percentage of that space devoted to medical treatment, tailoring and grooming (from as simple as showers to as complex as styling salons), food service and storage (for the things which cannot be grown in gardens), recreation and exercise (so humans don't go stir crazy), security (in case of conflicts or crime), training, education, and so on.

[Crakkerjakk]

I've always assumed that the whole "open space providing total life support" thing didn't leave it as an open space with rolling fields of wheat, but converted it into an extensive life support system, with algae, aquaculture, tilapia tanks, fauxflesh vats, etc occupying the entire space.

I suppose that's not really supported by the text, but I don't see how it could provide the life support any other way.

[David L Pulver]

Originally Posted by Crakkerjakk

I've always assumed that the whole "open space providing total life support" thing didn't leave it as an open space with rolling fields of wheat, but converted it into an extensive life support system, with algae, aquaculture, tilapia tanks, fauxflesh vats, etc occupying the entire space.

I suppose that's not really supported by the text, but I don't see how it could provide the life support any other way.

That's the only way it would work, yes.

[The Colonel]

I might add that there's no reason for total life support to be common unless you're in a no-FTL setting. Even as described it's complicated and involves all sorts of fussy components and a boatload of different skills to keep it working.
Compare to real life SSBNs - they spend months in what might as well be hard vacuum (except for a bit of water desalinisation), without contacting any source of re-supply and yet no-one has yet shown any interest in producing food aboard one.

[Fish]

On the other hand, it is not impossible to imagine certain safety regulations for starship design, in a sufficiently robust starfaring culture. This might not equate to "full life support," but to something like

Originally Posted by White Star Spacecraft Ltd Regulations Manual, p. 217

HEALTH AND SAFETY
In accordance with Galactic safety protocol, minimum essential foodstuffs must be provided by the Carrier not to be fewer than two (2) days food, water and atmosphere for each crewman and passenger for intrastellar voyages, and not fewer than five (5) days food, water and atmosphere for interstellar voyages.

[martinl]

Originally Posted by The Colonel

I might add that there's no reason for total life support to be common unless you're in a no-FTL setting.

Or any setting where the required endurance is relatively low compared to the population/volume of the ship, really.

However, with relatively good tech (bio or chemical), a "box" that takes in flexible raw materials and energy, takes the atoms it wants, and re-constitutes them as basic foodstuffs seems quite reasonable.

Note that the "biotech" version of this might be a "farm," only the light is high intensity monochromatic near-UV, the nutrients are pumped through constantly because they are consumed at an amazing rate, and "harvests" are hourly is not at all biologically unreasonable.

[The Colonel]

Originally Posted by Fish

On the other hand, it is not impossible to imagine certain safety regulations for starship design, in a sufficiently robust starfaring culture. This might not equate to "full life support," but to something like

Granted, but that's not life support ... that's a larder. Probably a fridge for a small crew...

[The Colonel]

Some Sci-fi examples:
Star Trek - uses replicators. Not all that interesting.
Babylon 5 - long life packaged food appears to be the norm: fresh plant matter is expensive and fresh meat a luxury (e.g. when Marcus makes Ivanova the extravagant - and culturally insensitive - gift of a bacon and egg breakfast). They have FTL, but travel times from faming capable planets are still fairly long.
Firefly - no FTL, but the setting behaves as though it were FTL. The entire headcount of Serenity is fed from what strongly resembles a C20 domestic kitchen (although it could pass for C19 since I don't recall a fridge). For some reason they mostly live off tinned food, which is odd given that they keep landing on low tech planets and fresh food should be way cheaper and easier to get hold off.