[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.