Author Topic: Water, Methane, and Oxygen ISRU on Mars  (Read 9620 times)

Offline Warren Platts

Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #40 on: 10/16/2016 12:02 AM »
There might be groundwater in certain places underneath permafrost. Permafrost is impermeable to liquid water, so makes a good cap rock that prevents escape to the surface. As you go deeper, the temperature must of necessity increase to a point that is not subfreezing anymore. At such depths, the overburden pressure is over an atmosphere, so liquid water would necessarily form.

It is much easier to drill for such water--assuming it exists and can be found--than practically any other option on the table IMHO. It would take some prospecting for sure, but maybe not a whole lot, relatively speaking.

The other strategy extreme seems to be to engineer for average conditions. That way the entire prospecting step can be eliminated, while success is guaranteed. But the latest round of studies has mainly succeeded in showing how difficult that is.

YMMV

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Offline Warren Platts

Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #41 on: 10/16/2016 12:05 AM »
Very old school (1970) study of groundwater in permafrost regions in Alaska. Of relevance to Mars ISRU however, IMO.

http://pubs.usgs.gov/pp/0696/report.pdf
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline lamontagne

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #42 on: 10/16/2016 12:19 AM »
Failure to even consider atmospheric water collection is a major over-site in the paper.  It is clearly the source which is most widely distributed and most easily processed, the technical challenge is basically just a sufficient power supply which is something that needs to be cracked anyway.

Atmospheric extraction was considered and ruled out.  See p26 of presentation.
Quote
1 kg water is contained in 250,000m3 of atmosphere

Quote
The air handling system implied by these calculations would be on the same order of magnitude as the largest air compressors known on Earth: ~600,000 CFM, requiring 65 megawatts to run, and roughly 5x5x10m in size.
CONCLUSION: The mass, power, volume, and mechanical complexity of the system needed for this approach are far outside of what is practical for deployment to Mars.

And here they didn't even include the power required to get water back out of the zeolite... which is far from trivial.
Using compression to extract water from the air is a really kind of silly.  I don't feel their investigation into atmospheric water was serious or complete.  However, this in not very important as mining for water is by far more effective than extracting it from the atmosphere, even if we use the best atmospheric extraction system, rather than the worst ;-)

Online AncientU

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #43 on: 10/17/2016 12:59 AM »
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.
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Offline Robotbeat

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #44 on: 10/17/2016 02:08 AM »
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.
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.
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Online AncientU

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #45 on: 10/17/2016 11:14 AM »
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.
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.

Would b much more efficient... that's exactly what 'mining' the regolith is.  It will naturally (gradually) recharge by condensing the atmosphere's load of water each sol.
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Offline Robotbeat

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #46 on: 10/18/2016 02:36 AM »
It's really more like farming, isn't it? If you just had fields of these hydrating minerals, it'd be more efficient than raw regolith, since you have to heat up all the regolith, but only part of it yields water.
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Offline Chris_Pi

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #47 on: 10/18/2016 04:15 AM »
It's really more like farming, isn't it? If you just had fields of these hydrating minerals, it'd be more efficient than raw regolith, since you have to heat up all the regolith, but only part of it yields water.

Very flexible on when/if processing steps are done as well. Once the stuff's spread out it can be picked back up early if you want some water at lower yields, Just left there if there's no need for it or collected and dumped into a storage pile if a new batch is ready to go back out.

Of course somebody making maps is going to have to label the area Tatooine. It's practically mandatory.  :D

Offline redliox

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #48 on: 10/18/2016 09:19 AM »
Of course somebody making maps is going to have to label the area Tatooine. It's practically mandatory.  :D

Or Arrakis, Vulcan, Geonosis, Korhal...

Desert planets are a surprisingly overdone theme in sci-fi I realize.  :P
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Offline Chris_Pi

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #49 on: 10/19/2016 06:09 AM »
Of course somebody making maps is going to have to label the area Tatooine. It's practically mandatory.  :D

Or Arrakis, Vulcan, Geonosis, Korhal...

Desert planets are a surprisingly overdone theme in sci-fi I realize.  :P

It's not the desert planet reference, It's the moisture farm one. Maybe Arrakis can kind of squeeze in there too if if a structure that increases airflow over the anhydrite beds makes sense. Some sort of windtrap or something...  :P

Offline john smith 19

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #50 on: 10/19/2016 11:24 AM »
Of course somebody making maps is going to have to label the area Tatooine. It's practically mandatory.  :D

Or Arrakis, Vulcan, Geonosis, Korhal...

Desert planets are a surprisingly overdone theme in sci-fi I realize.  :P
Well in that case I'd suggest calling the place Beta Colony except for the issues around such a name.
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Offline sevenperforce

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Re: Water, Methane, and Oxygen ISRU on Mars
« Reply #51 on: 04/28/2017 03:25 PM »
Seems like a good a thread as any for this question:

Is there any concrete idea about sizing a reusable soil-mining ISRU unit? Suppose you have a vehicle which can deliver and deploy up to 40 tonnes of payload to the surface of Mars, in a cross-section roughly the size of the Falcon 9 fairing. Is that enough for a reusable LOX/CH4 ISRU system -- one which can be deployed by the vehicle, process regolith to extract water, convert the water and collected atmosphere into LOX+CH4, fill the vehicle's prop tanks, dump the used regolith, and start again?

Kicker: it needs to be re-stowable in the vehicle, so that the vehicle can head back up to orbit, transfer the collected propellant to a tanker, and then return to the Martian surface in another location to start again.

Doable?

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