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About the resupply missions in "The Martian".
On 03/11/15 14:56, Robert Clark wrote:
Two instances were discussed in the film where unmanned cargo ships were mentioned to send up supplies to extend the time Whatney or the crew of the Hermes could survive. [...] BTW, since this is in regards to "The Martian", for you chemistry heads out there, are there some foods, liquids, or common materials that might be on the shuttles that could have filtered out the CO2 in air other than the lithium canisters? For instance perhaps the solubility of CO2 in water is different than in O2 and there could have been a way to separate out the CO2 from the air that way. Lithium (peroxide) canisters do not just absorb carbon dioxide, they also produce oxygen: 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2 ie about half the oxygen previously absorbed and turned into CO2 by the astronauts is given off. One method for getting rid of excess CO2 might be to heat the used lithium canisters using eg a mirror and sunlight, and then reuse the canisters; but lithium carbonate does not decarboxylate easily, it takes about 1300C. There are several ways to reversibly absorb CO2, including eg the use of zeolites, molecular sieves, activated carbon, the mixed-metal-oxide system used on the Shuttle, or the amine system used in the Space Station. -- Peter Fairbrother |
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About the resupply missions in "The Martian".
Peter Fairbrother schrieb:
Lithium (peroxide) canisters do not just absorb carbon dioxide, they also produce oxygen: 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2 Actually, it is water that is being produced. The net reaction is 2 LiO + CO2 -- Li2CO3 + H2O which is understandable because water is a much lower energy. |
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About the resupply missions in "The Martian".
On 07/11/15 21:24, Thomas Koenig wrote:
Peter Fairbrother schrieb: Lithium (peroxide) canisters do not just absorb carbon dioxide, they also produce oxygen: 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2 Actually, it is water that is being produced. The net reaction is 2 LiO + CO2 -- Li2CO3 + H2O There is no hydrogen in the input to your reaction to produce the water in the output of your reaction. It does not balance, in atomic terms. Some early spacecraft canisters used lithium hydroxide or hydrated lithium hydroxide instead of lithium peroxide, which would produce water: 2 LiOH + CO2 - Li2CO3 + H2O or for hydrated lithium hydroxide: 2 LiOH.H2O + CO2 → Li2CO3 + 3 H2O Lithium hydroxide is still used in some other CO2-scrubbing-of-breathing-gas applications, eg scuba rebreathers and submarine emergency systems - but it isn't often used in spacecraft nowadays, lithium peroxide is generally preferred. -- Peter Fairbrother |
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About the resupply missions in "The Martian".
Thomas Koenig wrote:
Peter Fairbrother schrieb: Lithium (peroxide) canisters do not just absorb carbon dioxide, they also produce oxygen: 2 Li2O2 + 2 CO2 ? 2 Li2CO3 + O2 Actually, it is water that is being produced. The net reaction is 2 LiO + CO2 -- Li2CO3 + H2O You start with two lithium, four oxygen and a carbon. You end with two lithium, four oxygen, a carbon and a hydrogen. There's a serious problem here. which is understandable because water is a much lower energy. -- We are geeks. Resistance is voltage over current. |
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About the resupply missions in "The Martian".
On 08/11/15 04:43, Robert Clark wrote:
The shuttles may have been changed at some point to use regenerative methods to reclaim the oxygen from the CO2, however, Columbia was still using lithium hydroxide: http://io9.com/how-nasa-might-have-b...-cr-1531638458 You are correct in that Columbia used LiOH canisters for primary CO2 scrubbing (though I don't think anyone suggested regenerative methods were used for oxygen regeneration). NASA qualified a regenerative solid amine bed based CO2 scrubber system for the Shuttle, but afaik it was never used in flight. I've done a bit of research, and contrary to what I had thought (and several references saying otherwise), metal-oxide regenerative scrubbers were not directly used in Shuttle. My apologies for the error. Regenerative Metox scrubbers were used in the later Shuttle/ISS EMUs, (early Shuttle IMUs used LiOH) - but Metox was not used in the main Shuttle cabin. On regeneration the CO2 was released back into the cabin or the ISS, and finally absorbed by the ISS systems, or occasionally by the Shuttle lithium hydroxide system. On ISS, Metox scrubbers are still used in the NASA ISS EMUs and the airlocks, but not in the ISS cabin itself - on regeneration the CO2 is again released back into the cabin, and finally absorbed in ISS systems, which consist of the zeolite molecular sieve (US CDRA) and amine-based (Soviet Vozdukh) regenerative systems, with lithium hydroxide canisters for backup. -- Peter Fairbrother "Peter Fairbrother" wrote in message ... On 07/11/15 21:24, Thomas Koenig wrote: Peter Fairbrother schrieb: Lithium (peroxide) canisters do not just absorb carbon dioxide, they also produce oxygen: 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2 Actually, it is water that is being produced. The net reaction is 2 LiO + CO2 -- Li2CO3 + H2O There is no hydrogen in the input to your reaction to produce the water in the output of your reaction. It does not balance, in atomic terms. Some early spacecraft canisters used lithium hydroxide or hydrated lithium hydroxide instead of lithium peroxide, which would produce water: 2 LiOH + CO2 - Li2CO3 + H2O or for hydrated lithium hydroxide: 2 LiOH.H2O + CO2 → Li2CO3 + 3 H2O Lithium hydroxide is still used in some other CO2-scrubbing-of-breathing-gas applications, eg scuba rebreathers and submarine emergency systems - but it isn't often used in spacecraft nowadays, lithium peroxide is generally preferred. -- Peter Fairbrother |
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