[Spaceships] Total life support

[Fish]

Originally Posted by Ulzgoroth

Well, that'd be rather problematic considering that it takes the same amount of space regardless of the size and/or range of the ship.

I disagree. You could fit a crate of dried oranges in a much, much smaller space than is required to put an orange tree complete with atmosphere, temperature controls, fertilizer, human waste reclamation, water, and so forth. Of course, the dried oranges only last a limited time — but a properly designed self-perpetuating orange tree biosphere can last for many years. (It might even last forever, but then you'd need things like self-repairing machinery, self-cleaning filters, and so forth. I imagine a typical space-based food factory has to have regular planet-side maintenance every few years, just like any other piece of complicated machinery, to replace any pieces which become worn or unusable.)

The question is, what do we mean by "life support?" Do we mean stored food? Or do we mean continuous, infinitely renewable food production?

[Ulzgoroth]

Originally Posted by Fish

I disagree. You could fit a crate of dried oranges in a much, much smaller space than is required to put an orange tree complete with atmosphere, temperature controls, fertilizer, human waste reclamation, water, and so forth. Of course, the dried oranges only last a limited time — but a properly designed self-perpetuating orange tree biosphere can last for many years. (It might even last forever, but then you'd need things like self-repairing machinery, self-cleaning filters, and so forth. I imagine a typical space-based food factory has to have regular planet-side maintenance every few years, just like any other piece of complicated machinery, to replace any pieces which become worn or unusable.)

The question is, what do we mean by "life support?" Do we mean stored food? Or do we mean continuous, infinitely renewable food production?

Well, aside from the definitional statement "total life support that grows or manufactures food"...

My point was that a crate of dried oranges per person might be mission-long food supplies for some ships (or more accurately some missions), twice as much as you need for others, and a hundredth what you need for others. Total life support weighs the exact same per person for all of these ships. Therefore, total life support is nothing like crates of dried oranges.

[Agemegos]

Originally Posted by Trachmyr

One of the problems is with the level of abstraction used in spaceships.

Indeed. And let me say that in general I am a big fan of the "back-of-envelope" level of abstraction employed in Spaceships.

It's just that as we do specify down to the "cabin" level, in which a cabin is a fixed size/mass rather than a fixed proportion of the ship, I do see an opportunity to do slightly better at the cost of only a little trouble. And this is something I would be interested in doing in some cases.

[Agemegos]

Originally Posted by Ulzgoroth

Total life support weighs the exact same per person for all of these ships. Therefore, total life support is nothing like crates of dried oranges.

Actually, total life support is exactly the same per ship using the approach with a replicator or an "open space" garden/farm, regardless of the number of people or the length of the trip. It is only when using the habitat-enhancing approach that the burden is the same per person on all missions. And that is a rather inefficent approach, one that you would only take if the number of crew and passengers required on the trip were small compared to teh capacity of one habitat system.

[David L Pulver]

Originally Posted by Brett

Actually, total life support is exactly the same per ship using the approach with a replicator or an "open space" garden/farm, regardless of the number of people or the length of the trip. It is only when using the habitat-enhancing approach that the burden is the same per person on all missions. And that is a rather inefficent approach, one that you would only take if the number of crew and passengers required on the trip were small compared to teh capacity of one habitat system.

For more realism, assigning a number of persons supported per area that a open space provides would be better.

[Crakkerjakk]

Originally Posted by David L Pulver

For more realism, assigning a number of persons supported per area that a open space provides would be better.

Perhaps with a TL modifier.

[Agemegos]

Originally Posted by David L Pulver

For more realism, assigning a number of persons supported per area that a open space provides would be better.

How do you feel about a number of persons supported per cabin at sufficiently high TLs?

[Agemegos]

Originally Posted by Fish

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.

Well, if you take a look at the description of habitat systems given on p. 17 of GURPS Spaceships, you will see that "[a] habitat includes a pressurized hull, radiation shielding, and a variety of standard features such as airlocks, hatches, compartmentalization, and elevators", besides which cabins, cells, and bunkrooms "have sanitary, galley, and dining facilities appropriate to their size and quality." Medical treatment, recreation and exercise, training, education, and especially so on are provided in specialised rooms for habitats (p. 18), such as briefing rooms, establishments, labs, offices, and sickbays; or in open areas (p. 19) such as auditoriums, gardens, theatres, and zoos.

With a little bit of arithmetic, you will discover that a "cabin" masses about eight tons. Rather generously allowing 2.5 m by 3 m of deck and a 2.5-m overhead I get 48 m^2 of deck, overhead, and bulkhead, and if those are 6mm thick that's only 0.03 m^3 of material. 2.2 tons of walls if they are 1/2" steel shared between adjacent compartments, maybe half a ton of walls if they are structural composite material of some sort. Even adding in the passenger's luggage, air and water reserves, pro-rata of life-support equipment, and furniture and fittings to mass three times what the walls do, I reckon you can get twice as much of everything else (bathrooms, accessways, lounge and dining facilities) as you have actual cabin space.

Even habitat systems that are represented as consisting entirely of cabins are only 30% cabin or less. The rest is airlocks, hatches, compartmentalisation, elevators, and sanitary, galley, and dining facilities. On top of that there are any briefing rooms, facilities (bars, brothels, casinos, gyms, massage parlors, nurseries, salons, classrooms, or retail stores), labs, offices, or sickbays that might have been represented explicitly.

[Trachmyr]

I actually houserule that Habitats for smaller vessels that do not require significant transport/elevators/hallways/etc. AND that have only spartan dining & sanitary facilities (Like Military Housing, 2 cabins share a small bathroom, minifridge & microwave), can be read as if +1 SM for determining quantity. This matches very well to the suggestion that actual cabin tonnage account for only 30%.

While higher TL ships may be able to afford the room of more generous accomodations, lower TL ships and many higher TL military vessel designs may benefit greatly from "Spartan Habitats". This becomes even more useful on small vessels that might otherwise be denied Habitats (& even smaller vessels using oversized modules).

Just food for thought.

[The Colonel]

Originally Posted by David L Pulver

For more realism, assigning a number of persons supported per area that a open space provides would be better.

This is where our stacking limits return ... for example the RMS Queen Mary was designed for about 2k passengers by 1934 standards (~700 each first and second class and about 600 steerage) and a bit over a thousand crew.
As a troop ship she carried 15-16k men per run.