Quote from: AncientU on 10/17/2016 12:59 amI believe the compression is needed to get sufficient flow rate through the zeolite beds to achieve the water extraction rate needed. Cannot just open a canister of desiccant and expect a significant capture rate by diffusion alone -- gotta pump 250,000cubic meters of Martian atmosphere through the beds to get one liter of captured water.There may be ways to use natural flow to extract water from the atmosphere.In fact, you could mine gypsum, extract water from the gypsum, and dump the anhydrite back onto the surface where it will slowly reabsorb water from the atmosphere and become gypsum again. In fact, you could have sheets of something like gypsum or other hydrated minerals that you harvest periodically, dehydrate, then place back onto the Martian surface to reabsorb water. Perhaps arranged vertically along with the direction of the wind to maximize flow rates and areal density of plates.I bet that'd be more energy efficient.
I believe the compression is needed to get sufficient flow rate through the zeolite beds to achieve the water extraction rate needed. Cannot just open a canister of desiccant and expect a significant capture rate by diffusion alone -- gotta pump 250,000cubic meters of Martian atmosphere through the beds to get one liter of captured water.
One thing I'd like to ask here. Fairly simple.If you only consider sites on Mars that are of relevance for exploration. Which I presume tends to limit things to under 20-25 degrees from the Equator.What do we actually know about the presence of water, how deep and in what form and quantity?In other words, given realistic landing sites, what are we dealing with and also how probable is it? In other words do we need to land a probe beforehand to be certain of the resource?It seems to me that ISRU for water on Mars comes on one of the following forms:1. Water vapour2. Hydrates and other forms of water bound to soil.3. Thin layers of ice of some reasonable purity of unpredictable depth and possibly localised scope near surface (1-2m at most)4. Thicker ice, but with some certainty and located deeper (up to about 30m).Lets consider those in turn.
That's some fascinating info but some of it will need modification, you can't separate out the CO2 in an exchanger bed, it's a major component. Russel's subseaquent post seems to be congruent with what you posted but could benefit from a critique that was more specific to what was sketched out.
Quote from: Lar on 02/04/2018 06:07 pmThat's some fascinating info but some of it will need modification, you can't separate out the CO2 in an exchanger bed, it's a major component. Russel's subseaquent post seems to be congruent with what you posted but could benefit from a critique that was more specific to what was sketched out.Carbon Dioxide has a significantly higher triple point than the other gasses. Is there some way of turning it into snow that falls into a container whilst filtering off the gasses?
Separating N2/Ar from O2 would be easy if not for the fraction of CO. These have close melting/boiling points and its unclear to me if ordinary fractionation can reduce the concentration of CO sufficiently. The answer may lie in separation/freezing at different pressures. But its a non trivial problem.
Separating N2 from O2 on Earth is relatively easy because you're not interested in absolute purity. CO on the other hand you need to get below a very low percentage not to be poisonous.
It should be possible to remove any impurities catalytic. Oxidize the CO to CO2. As a last step so not much of the O2 is lost.
Quote from: Russel on 02/08/2018 03:50 amSeparating N2 from O2 on Earth is relatively easy because you're not interested in absolute purity. CO on the other hand you need to get below a very low percentage not to be poisonous.It should be possible to remove any impurities catalytic. Oxidize the CO to CO2. As a last step so not much of the O2 is lost.
What about LOX-only ISRU on Mars?
What about the idea of bringing seed hydrogen for fuel production? That's 180 tonnes of methane + oxygen (enough to refuel the BFS) for every 10 tonnes of Hydrogen, no?
I'm puzzled by the 180 tonne figure just used for the BFS.
I'm puzzled by the 180 tonne figure just used for the BFS. I'd have thought it required a lot, lot more. Back to the reality of initial scientific/exploratory missions. Its easiest to import hydrogen in the form of liquid methane and simply ISRU the oxygen.Another portable (and non cryogenic) form of hydrogen is common ammonia which is 17% hydrogen by mass and has a room temperature density of 0.73 tonne per m3.In terms of density, liquid methane is 105Kg of hydrogen per m3 and ammonia is 129Kg of hydrogen per m3. Plus it is a source of nitrogen.