Assuming the standard configuration for the starship, rather than the "here's my shipping container unit and I'm sleeping the family in it in the cargo hold, pal", here's my take on the "two people per stateroom maximum" requirement: Life Support System Limitations.
Why this, rather than anything else? OK, in no particular order, then, here we go...
- CO2.
- Excretion Waste recycling capabilities.
- Temperature/climate control limitations.
The most obvious first. CO
2.
CO
2 is an obnoxious little bastard. You really can get on fine without it, but if it gets to a certain level, bingo, you're going to get hypoxia, and eventually die. No joke. This, from Kane International, Ltd.:
Code:
What are safe levels of CO and CO2 in rooms?
CO2
250-350ppm Normal background concentration in outdoor ambient air
350-1,000ppm Concentrations typical of occupied indoor spaces with
good air exchange
1,000-2,000ppm Complaints of drowsiness and poor air.
2,000-5,000 ppm Headaches, sleepiness and stagnant, stale, stuffy air.
Poor concentration, loss of attention, increased heart
rate and slight nausea may also be present.
5,000 ppm Workplace exposure limit (as 8-hour TWA) in most
jurisdictions.
>40,000 ppm Exposure may lead to serious oxygen deprivation
resulting in permanent brain damage, coma, even death.
CO
9 ppm CO CO Max prolonged exposure (ASHRAE standard)
35 ppm CO CO Max exposure for 8 hour work day (OSHA)
800 ppm CO CO Death within 2 to 3 hours
12,800 ppm CO CO Death within 1 to 3 minutes
Link:
https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms
Currently, there are devices designed to remove CO
2 from the air; they generally revolve around a set of chemicals being used to absorb this unwanted gas from the air of a closed system (submarines and spacecraft, for example), and have a finite limit on how much they can absorb before becoming useless. It takes a fairly comprehensive factory facility to manufacture these filters, and they likely cannot be made on-the-fly with the materials to hand in a ship in space. There will undoubtedly be other ways to recycle the CO
2 in ships in the future, probably involving specialist hydroponics (See the
Serrano Legacy series of books by Elizabeth Moon), but these WILL take up valuable room, and require specialist crew to maintain them. Until then, chemical 'scrubbers'.
EDIT: NASA Paper on Regenerative Carbon Dioxide Removal Systems.
NASA has has, on the ISS, a "Carbon Dioxide Removal Assembly" that is fully contained, and does not need additional consumables such as refrigerant gases, to operate. It's somewhat heavy reading, but interesting none the less. Link to PDF document:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050210002.pdf
I'd imagine that the tech for this would be advanced enough to remove (pun intended) the CO2 argument from this posting
Next up: Temperature/climate control limitations.
Everything mechanical and biological, when in operation, produces heat. Biological systems often also produce vapours, in the form of H
2O. Both of these, if unmoderated, will cause a ships systems all manner of harm. Wather vapour can be regulated by dehumidifiers, which have a fairly good record of having few mechanical issues, but which have a finite capacity, of course. Likewise, heat can be moderated by the inclusion of refrigerant units in the closed-system life support equipment, but these require certain additional parts to operate at peak or even reduced capacity, such as compressed refrigerant gasses, which if expended or missing, stops the units from operating, and hey presto, runaway thermal overloading of ships systems ensue; computers and excessive heat tend not to mix, after all. I have no idea how excess heat might affect, for example, Zuchai crystals in the Engineering section when it comes to jump transitions - nothing good, I would imagine, though.
Lastly, waste recycling.
Humans (and other biological entities) produce some truly disgusting waste products in the normal course of events - and let's not even discuss abnormal events, here, as it's bad enough with only the normal crap (sic) to deal with.
Liquid waste (urination products) can be recyucled easily enough, although you do get similar limitations as for CO
2, when it comes to this stuff. The processed and purified product is returned to the general potable water reservoir, the unrecyclable material (solids exist in urine as well, mostly microscopic) to the waste tanks to be flushed on connection to a starport waste extraction facility. The solid waste is vacuum dessicated (plenty of vacuum available from around a star ship in space, after all), the extracted vapours run through a similar system to the CO
2 scrubbers to remove harmful gasses (methane, for example), which are then generally vented overboard, with the remaining useful gas (oxygen, oddly enough), returned to the life support gas tanks, the remaining solid waste passed to a waste tank, to again be flushed empty on connection to a starport waste extraction facility.
The capacity of the waste tanks are, as you'd imagine, the limiting factor.
Now, these systems are designed by the ship manufacturer to have a capacity of perhaps four weeks maximum, based on a maximum of two people per stateroom for that period. That's at maximum capacity operation, a status that invites breakdowns much more frequently that you'd likely want.Imagine a breakdown in, for example, the water reclamation system, when then dumps (sic) a load of pure urine into the potable water reservoir
The above are reasons why you should not overload your cabins with people. Simple, innit
