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No chance. Solar has won the day and there is absolutely no evidence I have seen that Musk has any problems with that. Why would he? Solar panels have worked v well on Mars powering rovers and he is a major advocate of/player in the world of solar energy and battery storage.
At the moment, the sheer administrative and legal ball ache of trying to get a nuclear power reactor from Earth to Mars, has forced Musk to rely on a solar based solution. Maybe Musk can get a reactor from a non-US source ajd launch it from outside the US?
I have been looking into options for building reactors on Mars using local resources. Crude reactors could be built using natural uranium, but this requires that Musk brings a supply of heavy water with him. It would be very difficult to make that on Mars. But assuming the ability to make steel tanks and aluminium tubes, a crude pressurised heavy water reactor (or boiling heavy water reactor) would not be beyond the capabilities of a small Martian base. It would always be easier to build it on Earth and ship it to Mars. Maybe he could launch a non-fuelled reactor and natural uranium separately? Until it is assembled on Mars, it is just a steel tank full of heavy water.
Graphite moderated reactors are a much more challenging prospect, because the minimum critical core size is about 25 feet in a diameter. Calder hall was 30' in diameter and the graphite core weighed about 2000 tonnes. The power plant consisted of 4 units, each generating 200MW heat and 50MW of electrical power. The UK built this in 1956. It generated for nearly 50 years. If Musk intends to build a city of a million people on Mars, then native built Magnox reactors are something that could be produced relatively quickly using native resources and burning natural uranium. But you would need a sizable city to make a 50MW reactor a worthwhile investment. I wondered if it would be possible to build simpler, lower pressure units using graphite powder moderator and natural uranium metal bars houses in aluminium tubes. But there is no way around the minimum critical radius limit, aside from using heavy water. I think a small CANDU type reactor would be more practical.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Photovoltaic panels have worked so well on Mars that they couldn't provide enough continuous power to keep a rover alive that uses as much power as a 100W lightbulb. If delivered mass as a function of cost didn't matter, then your argument carries more water. JPL and NASA both disagree with your assertion, thus the KiloPower development program. Elon Musk's opinion would carry more weight the moment SpaceX successfully sends anything to the surface of Mars that requires multiple kilowatts of electrical power.
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He'll be delivering 300 tonnes to Mars. What makes you think he will lack energy? Somewhat different to the puny rovers which nevertheless have kept going remarkably well, far beyond their expected lives.
Photovoltaic panels have worked so well on Mars that they couldn't provide enough continuous power to keep a rover alive that uses as much power as a 100W lightbulb. If delivered mass as a function of cost didn't matter, then your argument carries more water. JPL and NASA both disagree with your assertion, thus the KiloPower development program. Elon Musk's opinion would carry more weight the moment SpaceX successfully sends anything to the surface of Mars that requires multiple kilowatts of electrical power.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis,
How many tonnes of anything has Elon Musk delivered to Mars or anywhere else outside of Earth orbit?
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We could build boiling sodium reactors on Mars that produce power using MHD generators without the need for argon cover gas or boilers. The Martian atmosphere is so thin and so inert, that sodium leaks would be non reactive. About 100 times the power density of Earth-based PWRs, few moving parts and many times cheaper. With a comparative advantage like that, maybe a Mars colony can manufacture refined metals for export to Earth?
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Nothing as yet...I am sure there was a time people said "And what has Columbus discovered as yet?".
Louis,
How many tonnes of anything has Elon Musk delivered to Mars or anywhere else outside of Earth orbit?
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Sodium leaks will burn in the CO2 atmosphere, Antius. I don't know how vigorous the reaction will be at the very low pressure, but it will certainly react.
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USN tried a sodium-cooled reactor in USS Seawolf SSN-585 back in the mid 1950's. They had serious problems with sodium coolant leaks, which means they had radioactive sodium fires inside a pressure hull while submerged. That's not a lot different than a mission on Mars. It was entirely unacceptable.
By about 1960-ish, USN ripped the sodium reactor out of Seawolf, and replaced it with a pressurized-water reactor similar to that which was successful in Nautilus, SSN-571, starting in 1954. Seawolf served for decades successfully. All US submarines have used some form of pressurized water reactor ever since, with an amazing safety record, better than that of the commercial nuclear power industry. They're up to generation 9 now, to the best of my knowledge.
All in all, that experience says use pressurized-water reactors on Mars. You'll need a distinct cooling system, since there is no seawater there to use as final coolant/heat sink. That is, unless you use a massive buried glacier as your heat sink. It's just a drilled well and piping to do that, and you get a whole lot of meltwater back up the well.
Can anyone think of good uses for that meltwater? Like propellant and breathing-oxygen manufacture? This occurs at the 10's-100's MW level, NOT the 10's-100's KW level! See posts 171, 172, and 173 in the "lightweight nuclear reactor, updating Mars Direct" thread, this topic.
GW
Last edited by GW Johnson (2017-10-10 18:22:59)
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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Conductive cooling is far more efficient than radiative cooling; check any heat transfer textbook. Besides, we have need of the thermal energy released for base heating and other uses.
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There is a way to make this work injecting steam or hot water down a well. But it will involve a lot of solids separation. The reactor coolant stream should be jacketed in some way to retain its cleanliness. And it's not the stream through the core, you use a heat exchanger to isolate that. All we need is to dump its heat into the buried glacier, and pump that meltwater back up the well. The well casing is not simple, in effect it is another heat exchanger, as well as a path to the surface for the meltwater.
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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Now you need a drilling rug and casing pipe, with a power source which is not dependent on the ice heat sink, all which will probably weigh more than the radiators would, even though they are less effective. Use of radiators also allows the power system to be put into service quickly. It also avoids possibly destabilising the glacier by basal meltwater lubrication which would imperil any structures on it or near to its end.
I would, at least initially, go for radiators until we have proved availability of other heat sinks.
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Well, if it were me, I'd situate to one side of the buried glacier, and slant-well drill out into it. From one basic wellhead, you can route a bunch of slant wells radiating out into the deposit, so that you can draw upon it for a long while. And with the well site not actually over the meltpoints, collapse isn't an issue. Just don't slant well drill under anything.
As for the radiator, that's exactly how you initially start the reactor at low power. Once the ice-mine well is drilled, you can transition to cold glacier as the heat sink, and ramp the reactor power way up. Power plus meltwater = electrolysis. Being who and what I am, I'd take a mix of everything, just to get started.
There's no accounting for the spread of "brain-dead" disease. I've never seen anything remotely like this idea proposed out of NASA or "old space".
If Musk actually does his big ship thing, he will inevitably have to do something like this to make his propellant. And, besides learning about the drilling business, he will have to get a license from DOE to take nuclear reactors to Mars. That takes a number of years to obtain, as the commercial power plant people can testify.
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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How do we know that we have a suitable place to do this? Years ago Canada developed a drilling rig but its mission got cancelled. Risking big expeditions with people shouldn't take place until the means of returning those people is established, so we must know that we will put them down in the right place. That requires a preliminary visit to prove what is on the ground, and below it.
Just because something looks like a glacier from orbit doesn't mean it would be useable. It could be a predominantly rock glacier (these occur on earth) or the ice may be so contaminated that you can't use the meltwater in a heat exchanger.
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Exactly! Which is why betting lives on ISPP for ascent propellant is bullshit for that first trip. Ground truth has always been at variance with remote sensing results. Sometimes far different.
That is not to say we shouldn't try such equipment out. But it is egregiously stupid and unethical to bet lives on that experiment, until after we know what really works and what does not at a given site. And human technological experience here says that the mix of what works and what does not will vary strongly from region-to-region on Mars, just like it does here.
Prior to the 1965 Mariner flyby, the "best" estimate we had was that Mars had a mostly nitrogen-some carbon dioxide-possibly a little oxygen atmosphere with a surface pressure of about 85 mbar, and afternoon equatorial summer temperatures as high as 80 F. Then until the 1969 orbital mission, our "best" estimates were that Mars was just about like the airless moon. It wasn't until the Vikings landed in 1976 that we found out what bullshit that 1969 assessment was. (The 1962 Mariner flyby at Venus showed what utter bullshit our earlier estimates were, so it ain't just Mars.)
The variance between ground truth and remote sensing at Mars has been shrinking ever since, due to the many landers plus extensive orbital missions, but it still is not zero. Not by a long shot. It cannot go to near-zero until men have visited in person every region on Mars, with deep-drilling rigs among other tools. Simple as that.
GW
Last edited by GW Johnson (2017-10-13 10:07:41)
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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With Musk size expeditions, visits to many parts of Mars become practical over a few decades. It's visiting the first half dozen sites that is in question to my mind. At least one of these sites must prove to be suitable for establishment of a base and industrial scale propellant manufacture so that earth returns may be made, broken items may be fixed and shelter and recreation made available. Finding that first site is essential before throwing any more money and men at Mars beyond the small crews needed to prove the site.
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I kind of doubt what we wish to find out about a site can be done robotically from inside a Red Dragon thrown by a Falcon-Heavy. Plus the Red Dragon thing seems to have been sabotaged by NASA excluding powered landings for crew Dragon.
I honestly don't know how to verify that the resources we need at any given site are really there, and further are of a quality that they can be processed and used successfully, without actually going there and attempting it with a crew.
And the BFR/ITS requires propellant manufacture in order for it to ever take off from Mars to come home. Something on the order of 250 tons of methane, and 750 tons of LOX.
Maybe an unmanned cargo BFR/ITS can be landed somewhere with some sort of propellant plant in its belly, to make fuel robotically somehow. But I don't really understand how that can happen without a supply of Martian water.
There is something called "moxie" that supposedly makes O2 out of CO2, with CO as a waste product. But I have no clue how mature or reliable this technology is, or whether we yet understand how to scale it up.
And then there's the power to run it all. If there's no crew, how do you set up enough solar panels at 0.38 gee, and how do you keep them clean? Or do you get the license from DOE to carry one or two SAFE-400's with your other equipment to Mars? How many KW do you need to make this work? Will it run 24/7/365 long enough to do the job before breaking down? (Everything breaks down, that's Murphy's Law.)
The only other way out is unmanned cargo ITS vehicles one-way to Mars as tankers with the return propellants as their cargoes. Nominally, cargo is 150 tons. To fly one ITS home requires something on the order of 1000 tons of propellants. That's 6-7 cargo tankers one-way to get one crewed ITS home, if ISPP fails. Plus sitting on the ground, there's no rear-to-rear docking to make the propellant transfers easy. And we're assuming they all come down close enough to utilize successfully, and further that none crashes and explodes. Somehow, I don't think that's what Musk had in mind.
He hasn't said exactly how he's going to address this chicken-and-egg problem. That tells me he and Spacex haven't thought that part all the way through yet. But they can be forgiven that lack for a while; concentrating instead on building the vehicles in the first place.
GW
Last edited by GW Johnson (2017-10-13 14:30:53)
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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I think where they land will be good enough for the first site. I don't think there will be any doubt that it will be OK for landing and surrounded by at least 5% water in the regolith, suitable for propellant manufacture. From that site A the Mars mission will be able to scout for the truly perfect location for the first Mars City - close or closish to good concentrations of water, iron ore, basalt, silica and a range of metals. I think most of the scouting will be done by robot vehicles and robot rocket hoppers.
With Musk size expeditions, visits to many parts of Mars become practical over a few decades. It's visiting the first half dozen sites that is in question to my mind. At least one of these sites must prove to be suitable for establishment of a base and industrial scale propellant manufacture so that earth returns may be made, broken items may be fixed and shelter and recreation made available. Finding that first site is essential before throwing any more money and men at Mars beyond the small crews needed to prove the site.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Maybe we consider the first few crews of volunteers as suicide missions, or at least "one way there?" Granted, some might find this idea noble and volunteer for it Get some old geezers to go--male and female. Be the true pioneers of the new world..
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Lol - no I think Musk will have crew safety at the forefront of his mind. As long as the cargo ships land as planned, I doubt there is much risk to the lives of the crew...well certainly no more than on the Apollo missions.
Maybe we consider the first few crews of volunteers as suicide missions, or at least "one way there?" Granted, some might find this idea noble and volunteer for it Get some old geezers to go--male and female. Be the true pioneers of the new world..
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis. Have you come up with a way of extracting the 1 te of water from each 20te of regolith (assuming you get all of it, which is unlikely) at a rate sufficient to make 1000te of CH4/LOX propellant in just two years? I haven't- not without big machines and a lot of heat.
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Well, given Musk plans to land 300 tonnes of cargo, I can't really see that standing in the way.
NASA have already researched how to do this - at least with lunar regolith analogue material:
https://www.nasa.gov/centers/marshall/n … 9-083.html
I guess you would be doing this on a bigger scale. I supposed the debate would be whether you have robot vehicles with a complete system on board that then collect the water, and spew out used up regolith (subsequently taking the water to a central facility, once their onboard water tank is full) or whether robot vehicles simply take regolith to be processed at a central facility.
I know there are industrial scale microwave ovens...
https://thermex-thermatron.com/industri … e-systems/
I guess in terms of water extraction you are looking to process maybe 25,000 tonnes of regolith or about 41 tonnes per sol on a 600 sol trip. Take 3 x 1.5 tonne robot digger/water processing rovers each processing 18 tonnes a sol - that's 100 scoops per hour of 30 kg per scoop (a mini digger can safely carry 130 kgs) on say a six hour shift. That would give you 54 tonnes per sol, so a bit of leeway. The mass of the rovers would be 4.5 tonnes a little significant but not a deal breaker where you have 300 tonnes of equipment being landed. If the rovers worked in a line, each one might be fitted with a microwave machine on their undercarriage to loosen the permafrost soil...so as it moves forward, the one behind has a ready made patch to dig into (but you would need an extra rover then to get your 54 tonnes per sol, as the front rover would not be digging). So, the scoops are taking place at a rate of 36 seconds per scoop cycle. That sounds about right to me, having seen mini diggers in operation. They would have to return to a central facility to deposit the water. If their water tank held 450 kgs of water, they would have to return to the facility every 2 hours - and that would obviously affect "productivity".
Putting it all together, maybe you would take 5 rovers - so that's a 7.5 tonnes mass allowance.
All this robot activity might be supervised by a couple of crew in a pressurised rover - so they can take radio control of the robots if unforeseen problem arise e.g. one hits bedrock or something.
I guess though, that simply having robot rovers collect regolith and return it to a central facility might have advantages (although you then have the problem of dealing with a sizeable amount of "spoil" at the central facility which is not so great). Overall I think I would go with smallish robot rovers that can, as it were, "hit the ground running" and avoid total dependency on one facility (I think that's generally a good principle for early Mars - numerous small units better than one big one that might fail).
Louis. Have you come up with a way of extracting the 1 te of water from each 20te of regolith (assuming you get all of it, which is unlikely) at a rate sufficient to make 1000te of CH4/LOX propellant in just two years? I haven't- not without big machines and a lot of heat.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Sorry. I put pencil to paper again. That’s what you have to do to determine feasibilities and thus the reality of the nifty ideas we generate and debate. Again, my intention is not to rain on any parades, just to figure out what might actually be more effective to attempt.
Off the Caterpillar website: front end loader 914M: 12,677 lb, 73.0 HP. Bucket capacities 1-1.6 cu.yd. In metric, bucket capacities .75-1.2 cu.m, weight 5749 kg, power 54.4 KW. This is a Diesel engine device. It would have to have all-electric propulsion and hydraulic power sources, and batteries that must be recharged, to operate on Mars. The rubber tires might work if not too cold-soaked, but tire heat requires power. The operator would need an MCP suit and Antarctic-type exterior clothing over it.
As a wild guess, 1 cu/m nominal bucket capacity, 6 metric tons, 60 KW max power rating running at duty cycle 35%. Wild-guess that it can operate for about 2 hr before requiring recharge, which is 0.35 * 60 KW * 2 hr = 42 KW-hr battery capacity. Lithium-ion batteries, charge energy = 1.5 * operating energy, as another wild guess, for 63 KW-hr to charge. (That factor is 2 for lead-acid batteries.)
To get one day’s 8 hr shift of working, will require 4 such machines, used one after the other, and recharged either during the off-shift, or while not working during the shift. Assuming you can dig up 1 bucket’s worth up and drive over to the point where it will be processed in only 5 minutes, then another 5 min back to the mine point, that means you get 1 cu.m of damp regolith to the processing machinery every 10 minutes. That’s 6 cu.m per hour, or 48 cu.m for the shift.
You get that 48 cu.m of regolith per sol using 24 metric tons of machinery, and with 252 KW-hr worth of battery-charging electricity. If you let it take all night to recharge (16 hr worth of off-shift time), that’s 15.75 KW worth of recharge power all night long. It’s dark at night, solar simply cannot do that.
If you recharge during the day (during the work shift), then you have the 6 shift hrs the machine is not working. That’s 42 KW to recharge. If the peak solar panel production is 0.5 KW/sq.m (at Mars with dimmer sun), and you use the typical 0.30 factor to account for low sun angles early and late in the sol, you will need >280 sq.m of absolutely-clean panels just to charge the batteries on the diggers.
The regolith is nominally 5% water by mass. Using a nominal specific gravity of 2 for loose particulate matter, 1 cu.m is 2 metric tons, 2000 kg. You get 48 of those bucketfuls per shift. 5% of that is water, so you got 4800 kg (about 4800 L) of water for your investment: 24 metric tons of diggers, half-a-hundred KW of electricity to keep their batteries charged, and either a SAFE-400 or >~300 sq.m of solar panel to get that electricity, for only 4800 L of water after an 8-hour shift. The crew needs to drink some of that, so not all of it could go toward propellant manufacture, or greenhouse experiments, etc. To get more water requires more machinery and more power, in proportion.
Now, think melting ice with hot water’s heat. In US customary, latent heat of fusion is 540 BTU/lbm. Specific heat of the liquid is 1 BTU/LBM-F. The temperature range I have to deal with is 212-32 =180 F. I need 3 lb of cooling water for every lb of ice I melt, theoretically. Call it 5:1 for real-world inefficiencies of heat transfer. Now I get to use hot water ice melting around the clock, not during a work shift.
Let’s arbitrarily pick 1 kg/s hot water flow rate as “typical” of what I can tap off the reactor coolant flow (probably not a SAFE-400, a real pressurized water design, but maybe there’s some sort of heat exchanger a SAFE-400 could use instead of the radiator it was designed for, I dunno!).
Using an Earth day of 86,400 sec to approximate a Martian sol, I have some 86,400 kg of hot water, which at 5:1 should melt some 17,280 kg of ice. So this kind of heat source should produce something like 17,000 L per sol! If instead I can safely tap off 10 kg/s hot coolant flow, the yield is closer to 170,000 L per sol! Something between those two figures should be easily feasible, though.
Does everyone now understand why I want to send hot water (could be reactor cooling water!!!) down a pipe into a buried glacier to melt ice in mass quantities (10’s-to-100’s of cu.m’s not just 100’s of L’s per day), and just pump it back up that pipe for a pump power likely well under a KW? The yield appears to be 2 to 3 orders of magnitude higher, while the effort and equipment required is far lower.
The same effort disparity is why our surface transportation here at home runs on oil, not coal, even though coal is where we started. Why go to all the effort and bother to run a strip mine for coal, when all you need is an oil well? Once the well is done, almost no effort goes into the continuing recovery.
The vehicle with the drill rig is likely smaller, lighter, and lower-power than one of these diggers. I need that drill rig, a few tons of drill pipe and well casing materials, and a lousy little water pump with a couple of spares. I only need it when drilling the well, although I may to drill another well after a while. Once the well is in place, if I use reactor coolant as my hot water source, the only power draw is the pump. That delivers tons and tons of water per sol to the inlets of the water-processing plants.
So, now judge: which is the better resource to exploit for water? Damp regolith, or buried ice? I vote for the buried glacier. Why? Less machinery to transport, less power draw while operating, and much more water per day available, to support all the various uses.
Damp regolith is mostly everywhere, but not entirely everywhere! Massive buried ice deposits are only in certain locations, which we think (!!) we have identified with remote sensing. There always has been, and always will be, a disparity between remote sensing and ground truth. That disparity can easily kill a crew equipped incorrectly for what the site actually offers, even if it is not a very great disparity at all. THAT is why the pathfinder mission(s) with some sort of deep-drill rig is so crucially important.
There is still simply no substitute for ground truth, especially subsurface ground truth. There is also simply no comparison between the concentrated resource versus the thinly-spread one.
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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Three points GW. First ,I had the idea I posted somewhere else, of filling rubber tyres with a solution of a radioactive salt (I proposed an alpha emitter). This would warm the tyres and the weight would improve traction. Water filling of tyres is a regular practice for the big machines that compact municipal dumps. Obviously it mustn't be allowed to freeze. This approach will give warm tyres for no power consumption.
Second point: I don't know that all the water in the regolith can be liberated that easily. Some may be adsorbed or absorbed and need more heat to desorb it and some may be water of crystallisation.
And third point: By melting the water in the regolith we will get muddy bleach not usable water. For that you will have to evaporate and condense it, or recrystallize it a couple of times.
Note that evaporation doesn't require heating to 100C (212F). That temperature depends on the pressure at which you operate your evaporator. You still have to provide the latent heat of evaporation but you recover most of that in your condenser.
Last edited by elderflower (2017-10-14 15:54:54)
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A few points:
I was proposing robot diggers, overseen by humans in a pressurised rover - no MCPs involved.
I think the rovers could be recharged by a specialist battery robot rover or by the human carrying rover.
I don't doubt buried or exposed ice is better than damp regolith as a resource but for Mission One, I think we should be prepared to accept a less efficient water resource. The priority for Mission One is finding a safe landing site.
I think a degree of scepticism about remote sensing is justified. But there is nothing to stop us landing somewhere landers or rovers have already been.
Sorry. I put pencil to paper again. That’s what you have to do to determine feasibilities and thus the reality of the nifty ideas we generate and debate. Again, my intention is not to rain on any parades, just to figure out what might actually be more effective to attempt.
Off the Caterpillar website: front end loader 914M: 12,677 lb, 73.0 HP. Bucket capacities 1-1.6 cu.yd. In metric, bucket capacities .75-1.2 cu.m, weight 5749 kg, power 54.4 KW. This is a Diesel engine device. It would have to have all-electric propulsion and hydraulic power sources, and batteries that must be recharged, to operate on Mars. The rubber tires might work if not too cold-soaked, but tire heat requires power. The operator would need an MCP suit and Antarctic-type exterior clothing over it.
As a wild guess, 1 cu/m nominal bucket capacity, 6 metric tons, 60 KW max power rating running at duty cycle 35%. Wild-guess that it can operate for about 2 hr before requiring recharge, which is 0.35 * 60 KW * 2 hr = 42 KW-hr battery capacity. Lithium-ion batteries, charge energy = 1.5 * operating energy, as another wild guess, for 63 KW-hr to charge. (That factor is 2 for lead-acid batteries.)
To get one day’s 8 hr shift of working, will require 4 such machines, used one after the other, and recharged either during the off-shift, or while not working during the shift. Assuming you can dig up 1 bucket’s worth up and drive over to the point where it will be processed in only 5 minutes, then another 5 min back to the mine point, that means you get 1 cu.m of damp regolith to the processing machinery every 10 minutes. That’s 6 cu.m per hour, or 48 cu.m for the shift.
You get that 48 cu.m of regolith per sol using 24 metric tons of machinery, and with 252 KW-hr worth of battery-charging electricity. If you let it take all night to recharge (16 hr worth of off-shift time), that’s 15.75 KW worth of recharge power all night long. It’s dark at night, solar simply cannot do that.
If you recharge during the day (during the work shift), then you have the 6 shift hrs the machine is not working. That’s 42 KW to recharge. If the peak solar panel production is 0.5 KW/sq.m (at Mars with dimmer sun), and you use the typical 0.30 factor to account for low sun angles early and late in the sol, you will need >280 sq.m of absolutely-clean panels just to charge the batteries on the diggers.
The regolith is nominally 5% water by mass. Using a nominal specific gravity of 2 for loose particulate matter, 1 cu.m is 2 metric tons, 2000 kg. You get 48 of those bucketfuls per shift. 5% of that is water, so you got 4800 kg (about 4800 L) of water for your investment: 24 metric tons of diggers, half-a-hundred KW of electricity to keep their batteries charged, and either a SAFE-400 or >~300 sq.m of solar panel to get that electricity, for only 4800 L of water after an 8-hour shift. The crew needs to drink some of that, so not all of it could go toward propellant manufacture, or greenhouse experiments, etc. To get more water requires more machinery and more power, in proportion.
Now, think melting ice with hot water’s heat. In US customary, latent heat of fusion is 540 BTU/lbm. Specific heat of the liquid is 1 BTU/LBM-F. The temperature range I have to deal with is 212-32 =180 F. I need 3 lb of cooling water for every lb of ice I melt, theoretically. Call it 5:1 for real-world inefficiencies of heat transfer. Now I get to use hot water ice melting around the clock, not during a work shift.
Let’s arbitrarily pick 1 kg/s hot water flow rate as “typical” of what I can tap off the reactor coolant flow (probably not a SAFE-400, a real pressurized water design, but maybe there’s some sort of heat exchanger a SAFE-400 could use instead of the radiator it was designed for, I dunno!).
Using an Earth day of 86,400 sec to approximate a Martian sol, I have some 86,400 kg of hot water, which at 5:1 should melt some 17,280 kg of ice. So this kind of heat source should produce something like 17,000 L per sol! If instead I can safely tap off 10 kg/s hot coolant flow, the yield is closer to 170,000 L per sol! Something between those two figures should be easily feasible, though.
Does everyone now understand why I want to send hot water (could be reactor cooling water!!!) down a pipe into a buried glacier to melt ice in mass quantities (10’s-to-100’s of cu.m’s not just 100’s of L’s per day), and just pump it back up that pipe for a pump power likely well under a KW? The yield appears to be 2 to 3 orders of magnitude higher, while the effort and equipment required is far lower.
The same effort disparity is why our surface transportation here at home runs on oil, not coal, even though coal is where we started. Why go to all the effort and bother to run a strip mine for coal, when all you need is an oil well? Once the well is done, almost no effort goes into the continuing recovery.
The vehicle with the drill rig is likely smaller, lighter, and lower-power than one of these diggers. I need that drill rig, a few tons of drill pipe and well casing materials, and a lousy little water pump with a couple of spares. I only need it when drilling the well, although I may to drill another well after a while. Once the well is in place, if I use reactor coolant as my hot water source, the only power draw is the pump. That delivers tons and tons of water per sol to the inlets of the water-processing plants.
So, now judge: which is the better resource to exploit for water? Damp regolith, or buried ice? I vote for the buried glacier. Why? Less machinery to transport, less power draw while operating, and much more water per day available, to support all the various uses.
Damp regolith is mostly everywhere, but not entirely everywhere! Massive buried ice deposits are only in certain locations, which we think (!!) we have identified with remote sensing. There always has been, and always will be, a disparity between remote sensing and ground truth. That disparity can easily kill a crew equipped incorrectly for what the site actually offers, even if it is not a very great disparity at all. THAT is why the pathfinder mission(s) with some sort of deep-drill rig is so crucially important.
There is still simply no substitute for ground truth, especially subsurface ground truth. There is also simply no comparison between the concentrated resource versus the thinly-spread one.
GW
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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