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Again, sorry. I should have mentioned direct CO2 electrolysis. Described in Robert Zubrin's book "The Case for Mars". He's aware additional oxygen is required, so he wants to use direct CO2 electrolysis. You take pure CO2, heat to about 900°C, and electrolysis across a membrane. CO2 on the inside of a zeolite tube, O2 passes through, CO2 and CO do not. Is it zeolite? Probably more than one catalyst can do it. About 80% of CO2 gets converted to CO. Dump that batch, start with a fresh batch of CO2. CO is a natural component in the atmosphere of Mars, so it isn't a contaminant. This makes pure O2 to top-up the LOX tank.
I noticed NASA got the idea of using a Sabatier reactor from Robert Zubrin's ISPP. But NASA used it for life support on ISS. So I thought we could us the other component. The Sabatier only consumes 50% of CO2 removed from cabin air, the other half is currently dumped in space. My idea is to run that other half through a direct CO2 electrolysis device. Since only 80% gets converted to CO, and the CO still has one of the two oxygen atoms, that means only 40% of O2 is recovered. However, 40% is better than 0%. They currently recover 0% of what's dumped in space.
I read the one NASA wanted to send on the Mars 2001 Lander would heat to 900°C. But here's a paper about it. I think the catalyst is different, and the abstract says 800°C.
Direct electrolysis of CO2 using an oxygen-ion conducting solid oxide electrolyzer based on La0.75Sr0.25Cr0.5Mn0.5O3 − δ electrode
Last edited by RobertDyck (2016-06-28 21:36:48)
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Hmmmm. A way to make oxygen from CO2. Very interesting. Any idea whether this or water electrolysis is better?
I see some awfully good experiments here to send to Mars, but I don't really see any Mars-based propellant manufacture technology yet. Something demonstrated in a science lab just is not generally a deployable technology.
Sorry, that's just the engineer talking.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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When you include energy to heat CO2 to the temperature required, direct CO2 electrolysis takes about 3 times as much energy per unit mass of O2, vs water electrolysis. And the current system on ISS with water electrolysis and Sabatier will recover 100% of oxygen from CO2 processed. I'm sure this is one reason they aren't considering direct CO2 electrolysis for life support on ISS. However, as I said, my idea is not to replace the current system, but to augment it. Using this to produce oxygen from CO2 that would otherwise be dumped in space. That could replenish recycling losses. And when you work out the total system including human metabolism, O2 produced from the current system comes from oxygen breathed by astronauts. It's recycled. But oxygen from CO2 currently dumped in space comes from dry carbohydrates in food.
Propellant production: If you only look at electrolysis, again CO2 electrolysis takes more power than water. However, you have to look at the whole system. CO2 can be recovered easily and reliably from atmosphere, and by freezing it out only at night it's quite energy efficient. However, we are currently only speculating about water ice. And we don't know how dirty or salty it will be, so how much energy to filter and desalinate? Reverse osmosis takes out the last of the contaminants and salt in one step, but desalination by reverse osmosis requires a lot of water pressure. That requires power for the pumps. It's more energy efficient than any other desalination system, but still takes a lot. Overall which is better? That depends on availability and quality of your ice.
And yup! I agree, we need to test ISPP before we commit human lives to it. This is one point I argued with Robert Zubrin. I said we need a robotic sample return mission; not for the sample, but just as a complete end-to-end demonstration of ISPP to return from Mars. Actually, I think we should have launched the Mars 2001 lander, with its ISPP-precursor. It would have only demonstrated harvesting CO2 from Mars atmosphere, and making O2. It wouldn't have included a Sabatier or supply of LH2, so no methane. But it was a good demonstration. Dan Goldin had ensured every experiment for Mars had a backup. One of the other instruments removed from the Mars 2001 Lander was a radiation sensor, to provide ground truth. There's a radiation sensor on Curiosity. So where's the backup for the ISPP-precursor?
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OK, there are ways to make methane and oxygen on Mars from local CO2, and from LH2 delivered from Earth, without any ice resource. Interesting indeed. Sounds like sufficient electricity will be the production rate-limiting factor. And liquifying them will not be cheap, either. Both are mild cryogens, subject to boiloff losses.
Too bad we don't yet have enough ground truth to evaluate ice as a resource. Ultimately, water electrolysis for in situ hydrogen and oxygen is probably (just my hunch) the right way to go in a longer-term scenario. The salt issue is the tough one. Apparently things got very salty and acidic billions of years ago as the planet dessicated.
My one-stage reusable lander for Mars sized out at 90.7 tons with NTO-MMH, versus 68.5 tons with LOX-LCH4, carrying the same 3.2 ton down-payload. The higher performance does help. Heat shield diameter is about the same, though, near 10 m.
GW
Last edited by GW Johnson (2016-06-29 09:49:01)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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OK, there are ways to make methane and oxygen on Mars from local CO2, and from LH2 delivered from Earth, without any ice resource. Interesting indeed. Sounds like sufficient electricity will be the production rate-limiting factor. And liquifying them will not be cheap, either. Both are mild cryogens, subject to boiloff losses.
Too bad we don't yet have enough ground truth to evaluate ice as a resource. Ultimately, water electrolysis for in situ hydrogen and oxygen is probably (just my hunch) the right way to go in a longer-term scenario. The salt issue is the tough one. Apparently things got very salty and acidic billions of years ago as the planet dessicated.
My one-stage reusable lander for Mars sized out at 90.7 tons with NTO-MMH, versus 68.5 tons with LOX-LCH4, carrying the same 3.2 ton down-payload. The higher performance does help. Heat shield diameter is about the same, though, near 10 m.
GW
Take a gallon of salty seawater and open up the container on Mars, what comes out of it?
Fresh water as it boils away.
What gets left behind?
Salt and other soluble that don't boil away.
I don't see what the problem is with salt water. Get a cold surface and put it right next to the boiling saltwater, and guess what condenses on it? Fresh water frost!, take that back inside your hab and it melts into fresh water! Desalinization is simple on Mars!
Last edited by Tom Kalbfus (2016-06-29 11:41:35)
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What you say is true, being the essence of vacuum flash distillation. The volume ratio is awfully high vapor/liquid at only 6 mbar, even at 0 C.
One would have to be very particular about exactly how one did this, because vapor that voluminous will tend to get lost in a strong outflow before it has a chance to touch a cold surface and condense as frost.
Haul the frost inside and put an atmosphere on it before melting it. That's easy enough.
I'm not sure what fraction of the water gets left behind in the concentrated brine, but I rather doubt that would be a serious problem.
This sounds like an excellent example of a relatively simple piece of equipment, which should be checked out in the lab at Martian conditions. Biggest problem is we don't yet really understand the composition of the salty ice resources, or how that varies from place to place. It's lots worse than just sodium chloride salt, from what I have read.
The kind of brine one would process in this way would come from a well drilled into a buried deposit. Inject hot steam to melt and pressurize the ice. You might need some sort of lift pump (at the bottom of the well) to get it out of the well. Longer term, you'll have to slant well drill in several directions from the well head, to avoid a giant cavern that could collapse under your feet.
Too bad we have no drill rig experience yet in Martian conditions. No one has yet tried that. But they should have, by now. Mariner 4 flew by Mars in 1965. We had two Viking landers on the surface in 1976. That's a very long time ago.
Lessee, the right site with a real buried ice deposit, a drill rig well with steam injection and a lift pump, a vacuum-flash distillation rig designed to function at 6 mbar or thereabouts, and a custom frost collector/capture device. That's all quite doable. I wish "they'd" just get on with the war and do it.
Add an electrolysis rig and you have hydrogen and oxygen. Add the sabatier device, and you have methane. You will need a very big source of electricity. Most factories of just about any type use lots of electricity. I'd hazard the guess we're talking about a nuclear steam generator here. MW-range? Depends upon how fast you want to make propellants, drinking water, and breathing oxygen.
GW
Last edited by GW Johnson (2016-06-29 12:25:03)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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AdAstra is a member in good standing with 584 posts on file.
The quote below is of the very first post by AdAstra, in 2003. Now 17 years later, my reading of the forecast of needs shows that much has been achieved.
Building a replacement for Columbia is not an option like it was back in 1986. As a nation and a member of the ISS coalition, the United States needs to move on. As part of the national recovery, and what will hopefully be a renewed emphasis on spaceflight, we must replace the shuttle at the earliest possible date.
I envision a three-pronged approach to doing so. First, DARPA increases funding for RASCAL, the responsive, reusable launch vehicle. The lessons and technology gained from RASCAL should be made open to the aerospace industry for incorporation into a new RLV.
NASA should financially support the X-Prize. Not directly, because that would violate the rules for the prize. But NASA can guarantee people and payloads that can be flown on board. For example, XCor plans on launching small satellites from its Xerus RLV. If NASA has suitable payloads, these small enterprises should be given the task of launching them.
Finally, we must proceed with Orbital Space Plane on an accelerated schedule. Issues such as booster safety and thermal protection that have plagued the Space Shuttle must be corrected in the process. Eventually, an unmanned RLV will be built to launch the OSP, finally giving us a fully-reusable vehicle.
We will remember the crew of the Columbia and carry on. Our astronauts must be given the best equipment for the dangerous tasks they undertake.
The X37b comes pretty close to a responsive, reusable vehicle, with the advantage (not foreseeable in 2003) of automated flight.
The SpaceX achievements include safe delivery of astronauts to the ISS.
There are private enterprise hard at work on the reusable space plane (for passengers) problem. Apparently 17 years was not quite enough time for that.
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The OSP, SLI, X37b plus others all got canned shortly after 2004 when shuttle was deemed unsafe for continued use. It was going to need upgrades and recertification to continue being used after station completion near 2010.
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