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One Marscat uses 134,280 watts in 3 hours of use. Two Marscats would use a total of 268,560 watts in 3 hours of use.
So, if you use the Marscats for 3 hours a day and recharge them for 21 hours a day they both need a combined 12,788 watts per hour to recharge and be ready the next day. That's a problem.
I think a big RTG would produce 600 watts an hour, two 10'x50' thin solar arrays would produce about 450 watts each (900 total), a thin solar array on the top of the Mars Hab covering the regolith would produce another 635 watts an hour, and a solar array on the entire outside of the Mars Hab would produce about 360 watts an hour. So, that's a total of 2,095 watts produced every hour in the day, and 600 watts an hour at night. That's not going to be enough.
How much power would a small nuclear reactor generate?
I think some time ago Spacenut posted a link to a nuclear reactor that was 30 feet wide.
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I found it, the Sandia Report 50-100 kwe gas cooled reactor. I just don't like all the moving parts compared to an RTG.
The two Marscat would use 268,560 watts total working 3 hours a day. So, they need 12,788 watts total recharge an hour to be fully recharged. So, we need to produce about 15,000 watts an hour of power all night long.
The Buk RTG makes 3,000 watts and weighs 2,200 lbs. If we increased it 5 times it would produce 15,000 watts an hour and weigh 11,000 lbs.
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The Kilopower reactors NASA and DOE are developing are 10kWe and total system mass (radiators, shielding, reactor core, electric generators) is 1800kg. These reactors use commercial LEU (Low Enriched Uranium), so you need a lot of Uranium (larger core, larger reflector, more shielding), but it's much cheaper than HEU (Highly Enriched Uranium), which is what SAFE-400 uses. Apart from the generators, it has one moving part, a single control rod inserted into the middle of a Uranium cylinder. That's pretty simple.
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The thing about needing all this power is it's only needed to recharge the Marscats for 21 days of digging, then they would build the habitats, then it might take them 10 days or so to bury the habitats with the Marscats.
Is there any way to reduce the size of the SAFE-400 to a smaller version that puts out about 15,000 to 20,000 watts? Or is it as small as it can get?
Also can you insert the control rod to activate it for a month or so, then pull out the control rod to deactivate it when it's no longer needed? Isn't that how nuclear power reactors work?
The crew could activate the smaller SAFE-400 for a month to recharge the Marscats. Dig out the habitat area, build the habitats, bury them, recharge the Marscats and deactivate the reactor.
Then, a year or so later, they would get a second shipment of buried habitat components and reactivate the SAFE-400 for a month to recharge the Marscats again.
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A good redirect is contained in the post copied here of GW's
Any crew in any scenario trying to survive an extended stay (about 13 months between 6-to-8.5 month transits) on Mars is going to need water, and is going to need oxygen. Not to mention food. And in multi-ton quantities.
Everyone on this forum and elsewhere bitches and moans about the cost of shipping those tons to Mars, always forgetting that the cost of a dead crew is far, far, far higher. Be that as it may, creating water, oxygen, and maybe food, locally on site is the only way not to have to ship those tons to Mars.
Now, it takes some sort of machinery to do those things, and those machines are tons that must be shipped. How big and heavy they are depends upon how much they must produce. Their success at producing may be dependent upon site conditions. So, it's a tradeoff, not an either-or situation.
If I need to produce 5 tons (an arbitrary number) of drinking water for a 13 month stay, that's a production rate of 5000 kg/(13*30 days) = ~13 kg/day. I may need much more that if I want to wash clothes or do any greenhouse irrigation. Yet most of these laboratory gimcracks I hear about are down in the grams to a kg per day.
These gimcracks are going to need a huge scale-up in size to support a crew on Mars. The gap between what is needed and what has been done is more than an order of magnitude. Scaling up the gimcrack means you ship tons of gimcrack instead of just tons of water.
Sooner or later, you shoot yourself in the foot, trying to concentrate and isolate a very diffuse resource. Go for the concentrated resource, and avoid all that. That's the smart thing to do.
Why process hundreds of tons of regolith (or hundreds of tons of 0.7% density atmosphere meaning hundreds of thousands of cubic meters) to get only a handful of tons of water? It's just too much effort for too little return. Doesn't matter that it's possible, it just ain't smart.
You want the buried glacier. The bigger, the better. Think tons of water per day, not kg. That is what sets up your base, and eventually your colony. And it would be trivially easy to connect a steam generator to one of the turbo-generator heat transfer points of a Safe-400 reactor rig. Let the solar PV do electricity; if you need heat, use a heat source. Direct. Simple. Efficient.
Now if you bet the lives of the crew on resource extraction like that, you'd better be damned sure the resource is really there. So, send a Red Dragon to the site with a robot drill rig and find out. Drill 100 m or more down to see. Do it for every potential site.
Which means guilt-edged priority number one for a manned mission to Mars is that pathfinding robot drill rig capable of 100+m even in hard rock. No one has such a device. It can be done, but has not been done. It must be done, and quickly!
You can make all the oxygen and hydrogen you want from that much water (tons/day). You can irrigate all the greenhouses you can build with that much water. You can make all the concrete or mud bricks you could ever use with that much water. Vast quantities of water is THE key! And pathetic little gimcracks producing water (or oxygen) at a few kg/day is NOT the way to get it.
To get what you need, you'd ship tons of these gimcracks, more tons of gimcrack for the more water and oxygen you think you need. There comes a point where you might as well just ship the tons of water and oxygen instead.
The way out of that impasse is to go for the concentrated resource, not the dilute one. Millennia of mining history are screaming that result at you, if you but have ears to hear.
GW
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One of the things forgotten about is the ability to ration what we do have and it has been worked on a bit at the analog society sites in that 1/3 less water can be done with no draw backs...
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The thing about needing all this power is it's only needed to recharge the Marscats for 21 days of digging, then they would build the habitats, then it might take them 10 days or so to bury the habitats with the Marscats.
I don't think it's a good idea to try to predict exactly how long a vehicle will need to operate. If it's there, you'll use it for something.
Is there any way to reduce the size of the SAFE-400 to a smaller version that puts out about 15,000 to 20,000 watts? Or is it as small as it can get?
There's a lower limit on how light you can make a viable fission reactor. The reactor can be really small, but output does not scale linearly with size. A 400kWe (not 400kWt, which is what SAFE-400 is) version of SAFE-400 is almost the exact same size. You're probably familiar with the term "critical mass". There's a lower limit to how much fissile material you can use to sustain a controlled chain reaction and there's also a limit to how thermally "hot" the core can get before it melts.
Awhile back, I had an argument here in the nuclear powered manned rover thread (Planetary Transportation subsection of this forum) with a moderator about what the smallest fissionable mass of material was for a controlled (nuclear reactor) versus uncontrolled (nuclear weapon) chain reaction and how core diameter relates to shielding if the objective is to minimize the total mass of the reactor system as much as possible and still provide adequate shielding for humans working in very close proximity to an operating fission reactor. His contention was that critical mass was the determining factor in how small the core could be. That's true to the extent that a critical mass of whatever isotope is required to reach criticality to begin with. Certain isotopes require much less neutron moderation and reflection mass as a function of their fission cross-section, a measure of how likely fission is to occur when the nucleus of an atom of the fissile isotope is struck by a neutron. Common fissile isotopes like U235 and Pu239 require neutron moderators (to "slow" neutrons to speeds likely to induce fission) and neutron reflectors (like the walls of a pin ball machine to bounce neutrons off of, except reflectors fling neutrons in every direction). That said, the diameter of the core dramatically affects shielding mass as a function of the square-cube law. Using Uranium or Plutonium requires rather thick neutron moderators and reflectors (Beryllium is about the lowest mass practical neutron reflector we have) and then the shielding has to surround the neutron reflector if humans are to be anywhere near the reactor during operation.
I wanted our nuclear scientists to research mass manufacture and use Am242m (a metastable isotope of Americium) to absolutely minimize core diameter. Am242m, like Pu238, is incredibly expensive to produce as a function of the energy and materials expenditure required to produce it. The reason I wanted to produce Am242m is that that isotope has a fission cross-section of thousands of barns, compared to hundreds of barns for U235 and Pu239, so it needs little to no neutron reflector surrounding the core to reflect neutrons to sustain a chain reaction. A film of the Am242m isotope less than one thousandth of a millimeter in thickness can sustain fission on its own without a neutron moderator or reflector of any kind.
For any practical purposes, an isotope as "hot" (in the radioactivity sense of the word) as Am242m will require some sort of alloying metal or must be produced in ceramic form to make the isotope usable for thermal power output without melting the isotope in the reactor or fissioning before we ever insert it into the reactor. Simply obtaining isotopically pure Am242m might work for making an insanely expensive and small nuclear weapon, but it'd be impractical for electrical power production. Pu238 (the isotope we use in our RTG's) is manufactured as Plutonium Dioxide, a ceramic metal, to increase the temperature at which it melts. Pure Plutonium metal melts at 639C, whereas Plutonium Dioxide melts at 2390C. Am242 metal melts at 1176C, so much like Pu238, we'd either alloy it with another metal or turn it into a ceramic to withstand the temperatures produced in a fission reactor and to somewhat "moderate" the radioactivity so we didn't have Am242m films many times thinner than a sheet of printer paper spontaneously fissioning while we were trying to manufacture it.
Also can you insert the control rod to activate it for a month or so, then pull out the control rod to deactivate it when it's no longer needed? Isn't that how nuclear power reactors work?
Yes. After the neutron "poison" (substance that absorbs so many neutrons that the fission chain reaction can't continue) is inserted into the reactor, the chain reaction stops in seconds to minutes. It'll be very close to throwing a switch in a very small reactor. Radiation levels produced fall dramatically in seconds to minutes. However, after a reactor is first taken critical for the first time, thereafter the components are radioactive because the byproducts from fission are radioactive.
Most people think that half lives of millions of years means "highly radioactive", but it's actually the opposite. If something has a half life of seconds or minutes, it's so "highly radioactive" that you won't be able to handle it. If it has a half life of millions of years, it's barely radioactive at all. These highly radioactive but short-lived isotopes (Cesium, Strontium, an Iodine isotopes, for example) are what we call "fission products" and are the reason you can't immediately work on a reactor after shutdown. The quantities produced in these very small reactors will also be small, but the isotopes will still be there and are highly radioactive for seconds to days after shutdown.
If you shut down a reactor of the sort that we're proposing to use on Mars, then humans can work on the reactor about two weeks later with minimal precautions taken. At that point, the natural environment of Mars will be more radioactive as a result of GCR's than the site where the reactor operated. The fission products captured in the Uranium, not the Uranium itself or the reactor itself, are what you have to concern yourself with. In any event, these reactors are designed in such a way that the Uranium fuel is never removed from the core for the entire operational life of the reactor.
The crew could activate the smaller SAFE-400 for a month to recharge the Marscats. Dig out the habitat area, build the habitats, bury them, recharge the Marscats and deactivate the reactor.
If you spend the money to ship a reactor to Mars, then you'll be using the reactor thereafter to generate power for a few decades. It's entirely feasible to vary output to extend the life of the core. If you're not using 100kWe, then turn the control drums inward or partially insert the rod to vary reactivity and thus output.
Then, a year or so later, they would get a second shipment of buried habitat components and reactivate the SAFE-400 for a month to recharge the Marscats again.
It's feasible, but in reality you want the power. Even if you're only using it to operate WAVAR or grow food or dig more holes for habitat modules, you'll always find uses for the power.
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I have posted as much of the MARSCAT discussion to the original topic that DOOK did start at http://newmars.com/forums/viewtopic.php?id=7527
The water I do feel that we have multiple solutions for, the air seem as well covered, the many cargo landers can be turned into habital space to which if we are not using any they are just what the doctor ordered for making greenhouse structures with until we need more area to grow within but its a start.
The power solutions from homopolar generators and super capacitors, batteries or all types and rtg's will cover the needs when we suppliment them with the atk solar fan assembly should be suffiecient for power.
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orbital mirrors and greenhouse gases can raise Martian atmospheric pressure above 150mb, humans could work on the surface without spacesuits. They would need warm clothing and protection against dust, but those are relatively easy problems to solve. In addition, an atmosphere that thick would shield out cosmic rays. This would be a huge boost to habitability and it can be accomplished relatively easily.
The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi; 6.0 mbar), about 0.6% of Earth's mean sea level pressure of 101.3 kilopascals (14.69 psi; 1.013 bar). It ranges from a low of 30 pascals (0.0044 psi; 0.30 mbar) on Olympus Mons's peak to over 1,155 pascals (0.1675 psi; 11.55 mbar) in the depths of Hellas Planitia.
This would require not only adding to the current amount but also changing the mix to a breatable content t tat low as compared to earth pressure level....
The Martian atmosphere consists of approximately 96% carbon dioxide, 1.9% argon, 1.9% nitrogen, and traces of free oxygen, carbon monoxide, water and methane, among other gases, for a mean molar mass of 43.34 g/mol.
So we drop larger nuclear powered MOXIE units to where the atmosphere is at its highest to start the process but where is the extra coming from?
We could land the nuke combo plant at the poles with more heat being released via contact to the isy conditions to aid in a great gas build up from the moxie units as well.
While we can capture moisture from the atmosphere and from the soil we still have not really made much of a change other than make more oxygen possible while needing storage tanks for the hydrogen if we process via electrolysis to gain the oxygen.
We will need to find nitrogen in the rocks to liberate as well for atmospheric build up but at what energy costs and process type?
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Not sure if this has been posted Extraction of Atmospheric on Mars for the Mars Reference Mission
The papers Article meantions hydrogen boiloff rate to which if we send seed hydrogen to make water with that we would be sending 7mt to get 2.6mT on mars after a 200 day journey. This amount would be able to make 23 mT of water for crews to have for 3 missions to the same site.
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It's really essential that the early missions be water prospectors! all of theses atmospheric water extraction schemes are energy intensive for a small return on the investment. If there is indeed a reservoir of water recently detected the size of Lake Superior, the most effective method would be as I described earlier: strip mining of regolith and transport of the frozen material to a processing center where it would be allowed to melt inside a pressurized environment. Dook ridiculed this idea since it would require centrifugation for complete water extraction, a process called in the chemical industry: "dewatering."
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I agree that the first several mission will not only be energy limited but also mass restricted as well to which the least shipped mass for execution of any thing that man requires to gain a toe-hold, followed by a foot-hold are critical to success and future colonization by man.
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I used to think that, until I read about water extraction from the Mars atmosphere...
http://www.lpi.usra.edu/publications/re … ington.pdf
This paper suggests we could collect 1.2 tonnes of water in just over 300 sols per Mars summer (over about 6 Earth years). Make that 3.6 tonnes over a 6 year pre landing period.
Given we can pre-land water and will be bringing substantial water from Earth along with the main human-passenger lander, I can't see how we will be short of water on Mission One, given efficient, ISS-style water recycling.
There is no need to have any doubt about there being enough water for six people forming part of a first Mission to Mars. Once there the pioneers can source more water - probably directly from the surrounding regolith (not need to go looking for a major glacier).
It's really essential that the early missions be water prospectors! all of theses atmospheric water extraction schemes are energy intensive for a small return on the investment. If there is indeed a reservoir of water recently detected the size of Lake Superior, the most effective method would be as I described earlier: strip mining of regolith and transport of the frozen material to a processing center where it would be allowed to melt inside a pressurized environment. Dook ridiculed this idea since it would require centrifugation for complete water extraction, a process called in the chemical industry: "dewatering."
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Another scheme to get water from the regolith, is to pick an ore that is high in hydrates and another that is high in oxides to blend into a chamber and then heat it such that we get a reaction that makes water.
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Yes, I did wonder whether to mention that. It's often overlooked but I find the chemistry a bit confusing!...
https://en.wikipedia.org/wiki/Water_of_crystallization
Another scheme to get water from the regolith, is to pick an ore that is high in hydrates and another that is high in oxides to blend into a chamber and then heat it such that we get a reaction that makes water.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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KISS! KISS!! K =Keep. I = It. S= Simple! S = Stupid!!
If water ice + regolith exists, simply "harvest" it in "cubit" size chunks, allow to melt, purify, drink, shower, wash clothes & dishes, w/o water rationing!
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I agree - eventually we will be able to accept a really good water source. But for Mission One, if we really need water in quantity, then I think it's got to be atmospheric extraction that is the key technology, as we can be guaranteed the water will be ready and waiting there for the Mission One pioneers.
KISS! KISS!! K =Keep. I = It. S= Simple! S = Stupid!!
If water ice + regolith exists, simply "harvest" it in "cubit" size chunks, allow to melt, purify, drink, shower, wash clothes & dishes, w/o water rationing!
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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I'm curious about the enthusiasm I see on these forums for water "producers" that extract water from Martian air or Martian regolith. They seem rather pitiful in output for the energy and/or effort required to run them, and awfully expensive items for no more production rates than they have.
Martian "air" has very little water to extract because (1) it is very cold, and (2) because it is so damned thin. I've seen some designs proposed for Earthly humidity extraction, and those are working with a maximum 4% of total pressure as the water vapor pressure, at 100% relative humidity. That vapor pressure 0.04 atm or less. On Mars, the relative humidity is low (under 1%) and the absolute humidity is very low indeed, plus the fact that the total "air" pressure is 0.7% that of Earth. I would be terribly surprised if the water vapor pressure on Mars ever exceeds 0.00001 atm, if not some factors of 10 lower than that. That is one dilute resource.
Martian regolith I have seen quoted as up to 3% water by mass. That certainly doesn't mean that all of it is that wet. But at 3%, you have to process 30 kg of dirt to get 1 kg of water. That's one measly liter. Just shoveling 30 kg dirt wearing one of those idiotic balloon suits will make you thirstier than that! If the average is closer to 0.3% water (that's wet for a desert, which Mars is, by the way), you get to shovel 300 kg of dirt to get that 1 liter of water. That's quite a dilute resource, but not as ridiculously dilute as the atmosphere.
On the other hand, if you go look for the buried glacier, you are looking at a resource that will be at least 50% water by mass, maybe above 90%. And you do not need to dig it up! Drill a well into the buried, put a pump at the bottom, then rub steam down the well pipe, and pump water back up. You're out the energy to run a steam generator (lots of low grade heat) and a pump (a little high-grade energy in the form of electricity). No shoveling, no driving backhoes. Just drilling once.
Heat and electricity both come from nuclear generators, by the way. A SAFE-400 produces 400 KW heat, from which it produces 100 KW electricity, while needing to reject 300 KW waste heat. Why not reject that heat (at least in part) to a steam generator? The temperature is high enough to drive a gas turbine. That's more than enough to make steam.
As for cleaning up the water, that's as easy there as it is here, maybe even easier because of that vacuum of an atmosphere. Do a settling tank to get rid of the solids (a 200 year old technology). Do vacuum flash distillation to get fresh water (a 100 year old technology that basically runs on waste heat). Run the salty water through an electrolysis rig (using the salts already in the water as your electrolyte) to create oxygen and hydrogen. Electrolysis requires electricity. You might not have enough with nothing but solar PV, but if you have nuke generator, no problem.
What is so hard about understanding the dilution problems trying to use a resource that is at best 3% concentrated, versus one that is at least 50% concentrated? This is millennia of mining experience and 150 years' of petroleum experience screaming at you, not me.
What's the point of nifty technological toys if 100+-year old technologies work much better, other than trying to make a buck off your investment developing the nifty toy?
GW
Last edited by GW Johnson (2017-05-22 16:26:27)
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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Earlier in theses discussions, I was ridiculed by Dook for suggesting use of a standard sewage dewatering centrifuge to deal with regolith mixed in the glacial water. That's basically what needs to be done prior to relocating a nuclear reactor/steam plant. I simply suggesting another 100 year old technology called blasting with explosives. That's the way coal is strip mined in trainload quantities. We can have a nice cart train filled with ice chunks, covered to slow evaporation/sublimation, drive to the processing dome, allow to melt, transfer to centrifuge, and the effluent goes directly to a vacuum stripper system. Product is clean and drinkable H2O. The by-product is garden soil.
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I agree that tapping into a glacier is the best option if we can get to one that is not remote to the first landing site location and does not contribute to risk to get that water. That said the soils are the next best location in general followed by the air supplemental water to cover losses in recovery of the life support system.
This is all done to keep the mass from earth not in an increasing manner and to allow for other items to be shipped to mars that are just as important once we have a working method.
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SpaceNut-
I'm simply applying my professional knowledge from the chemical process industry to what seems to be a very straightforward problem in chemical engineering.
This is also low tech methodology, based on 19th century stuff.
Last edited by Oldfart1939 (2017-05-22 21:30:54)
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Hi Oldfart1939:
I saw your proposal to mine dirty ice with blasting. That would be a fun job to do. I guess it depends upon just how massive and how dirty the ice deposit is. What did you have in mind for the explosives?
I know how they did it at the Mesabi Iron Ore range in Minnesota. Originally, it was shot holes packed with charcoal and wet down with liquid oxygen. That proved fairly dangerous to handle by the miners, so when ANFO became available, they switched to that as much safer to deal with. But, it did require substantially-bigger 9-inch diameter shot holes.
It does occur to me that if the buried glacier is massive enough, you can dispense with all that shot hole drilling with drilling just one big well (6-10 inches?) and do steam extraction down-hole. Might need one blast to crack it up, or maybe the steam pressure could do that job. Works pretty good with thicker petroleum residues here, and has for decades now.
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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GW-
I'd suggest using ANFO, since it's quite safe for those not necessarily "licensed blasters." There needs to be a series of components; the primary explosive, in form of blasting caps, an initiator, usually sticks of either dynamite or a much safer one made of Tetryl. then the substrate of ANFO. I got all this from a deceased friend of mine who was a licensed professional blaster, BITD.
I'd agree with the steam down the hole method, but a certain amount of fracking needs to be done with explosives in order for that process to become effective. That, and having the nuke plant in close proximity.
What others here are attempting to do with these chemical processing industry no-brainers is called reinventing the wheel.
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I'd agree with the steam down the hole method, but a certain amount of fracking needs to be done with explosives in order for that process to become effective. That, and having the nuke plant in close proximity.
Mark Homnick of the Mars Homestead Project convinced me of this. He wanted to use steam to excavate a cave in a glacier or frozen lake. Keep the roof of the cave intact, so steam stays contained. Obviously pressure would be released out the hole, but with a cold ice roof, much of the steam would condense and drip down into the pool you create at the bottom of the cavity. You could even seal the hole with plastic film, run outlet gas through a condenser. There's plenty of cold on Mars, so a condenser shouldn't be a problem.
Members of this forum convinced me of the frozen pack ice at Elysium Planetia. Further reading of published science papers from the European Space Agency clinched it. That formation was formed by a volcano that melted permafrost, then the water ran down hill and pooled in a low spot. The surface is frozen pack ice, indicating it cooled slowly enough to form pack ice. On Earth when that happens, surface ice freezes without salt. So surface ice there should be relatively clean, as clean as a fresh water lake. Ice at the bottom would have the salt. The trick is to melt the surface ice while maintaining an ice roof to contain steam and water vapour.
Last edited by RobertDyck (2017-05-23 18:27:11)
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Robert-
This supports my thesis of strip mining the surface of this once frozen lake. You and I have both supported the concept of using a Bobcat-type skid-steer front loader for early Mars missions. Big chunks of ice should be available readily after blasting a hole. The Bobcat-type loader could be used to fill several triangular cross section carts in a short "train," and thence hauled inside a habitat. More carts could then go back for another load. In a matter of just a few Sols, the mission would have an adequate water supply. The sediments can be removed with a small basket centrifuge, and should distillation prove necessary, the residue left in the distillation vessel should be minimal, consisting of non-volatile salts.
Last edited by Oldfart1939 (2017-05-23 15:45:39)
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