Monday, November 17, 2008

Crew Health Basic Numbers

These basic numbers are conservative estimates for a no-GCR/Solar storm shelter style space mission, and assumes that a really good closed physical life support system (CPLSS), as opposed to more advanced closed ecological life support system (CELSS). Note that I'm not arguing against CELSS, merely assuming that it will not be available for space cruise on early missions.

Mass per crew member:
85kg the naked crew member
15kg personal margin
30kg arbitrarily budgeted for shared medical equipment of best return on investment for mass
30kg transition suit (worn during dockings, ascents, entries, etc.)
30kg seat
20kg two spare transition suits for every three crew members
20kg kit to convert transition suit to EVA suit
15kg conversion kit spares (equivalent three for every four crew members, but will probably concentrate on high wear items, including gloves and CO2 adsorbent cartridges.)
5kg fire extinquisher
5kg personal computer
5kg personal medical kit (not to be confused with medical equipment above.)
10kg Emergency Open Life Support kit (i.e.: SFOG or superoxide cartridges to allow time for emergency life support shutdown during "shirtsleeve" periods. Does not protect against depressurization
50kg Margin for stuff I might not have though of, or underestimates in the above.
320kg total per astronaut

250kg pressure shell in the transition vehicle for each crew member (based on an average from several pressurized aluminum aircraft cabins)
90kg inflatable pressure shell for each crew member (a calculation based on the ASME B&PV Sec VIII, Div 1 spherical head formula for 15psig, 20ksi AWS, density 4.0kg/L material at three different diameters showed 4.5kg/m3 would be used...20m3/pax is a good cabin volume...hopefully you understand this if you're a pressure vessel engineer.)

660kg Total per crew member, fixed mass in space
2000kg Total per 3pax section (rounded up from 1980kg) Of this, 1250kg would be in the Cruise Hab during space cruises, and the other 750kg would be in the transition vehicle.

Unrecovered consumables per person day
2.0kg water (assumes 20kg of water used per day recycled at 90% efficiency)
1.0kg oxygen (assumes 2.0kg of oxygen used per day recycled at 50% efficiency...100% electrolysed water, 50% electrolysed or RWGS'd CO2, allows for leakage.)
2.0kg food
1.0kg solid waste (stuff like toilet paper, garbage bags, duct tape, commode chemicals, etc.)
1.0kg other/margin (stuff like bandaids, shampoo, laundry soap, toothpaste, socks, etc.)
7.0kg total per pax-day

500 pax-days per kit (after I figured out how much would fit in 6000kg, which just happens to be Stampede Lander's capacity.)

1000kg water (5% dunnage margin)
500kg oxygen (10% dunnage margin)
1000kg food (20% dunnage margin)
500kg solid waste (0% dunnage margin...i.e.: this is the dunnage for solid waste)
500kg other/margin (20% dunnage margin)
3500kg total

Values with dunnage margins (dunnage = tanks, lockers, packaging, etc.)
1050kg water
560kg oxygen
1250kg food
500kg solid waste
630kg other/margin (edit point)
3990kg total

This is the "supply trailer" package for non-ISRU life support, allowing for a 2000kg mobility system to accompany it. A first mission with six people requires N+1 supply trailer redundancy and 500 days of supplies. This results in seven supply trailers (yikes).

Space Supply Package: This one is more important because on the surface, we should be able to use ISRU water, although we'll really need seven supply trailers if we can't prove that we can make Mars water potable with the equipment the crew has on hand before they fly the first mission. Seed hydrogen for surface use has not yet been ruled out, but I'm not going to address it in this post.

A crew will need 15oo pax days for each leg of the journey, allowing 250 day cruises each way. For shorter cruises, it's easy to substitute equipment, or even increase the performance transfer for an even faster cruise (up to the limits of the lander's ability to arrive at Mars going fast.) The Space Supply Package is included with the Cruise Hab (has 1250kg on it already), to a limit of 14000kg. We've established 8kg/pax-day including dunnage, so the remaining 12750kg of Cruise Hab, 1594 crew days. This means that the 14000kg lift ticket is probably very close to the minimum necessary for a human to Mars mission. (This 14000kg is launched to a 24 hour assembly orbit, or to a libration point, which is why a 45 tonne class booster, in LEO terms, is required.)

Surface package (with 100% ISRU water and oxygen):
1.0kg solid waste/pax-day
2.0kg food/pax-day
1.0kg other-margin/pax-day

Supplies for 800 pax-days on surface:
800kg solid waste
1600kg food
800kg other-margin
3200kg total

With dunnage:
800kg solid waste
2000kg food
1000kg other-margin
3800kg total

Thus, with a requirement of 3000 pax days for a six person crew, four supply trailers are needed, and a fifth for redundancy at landing.

That's it for this post. More later

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