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

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.

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

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.

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