Maybe heat would work well for this. Place a large "lid" over a given area of ice. Begin heating the ice at the center of the covered area with a heating device in direct contact with the ice. Siphon off the resulting water vapor as it is collected in the lid. This could be scaled up or down. The lid would need to be large enough with respect to the amount of heat applied so that there is enough ice between the heated area and the limits of the lid so that water vapor does not escape at the edges. You could perhaps build mobile machines with lids of 1 to 2 meters, or scale the process up to setting up the lid and plumbing necessary to cover an area of hundreds of meters and then spend weeks harvesting that one area. Perhaps the lid should be a double lid to reduce heat transfer by the water vapor to the perimeter area of the lid.
One approach could be to melt the ice in place and suck out the resulting water. The ice will have to be melted anyway at some point if one has to use it.
I figure the ice deposits will be somewhat similar to the ice hardpan deposits of water ice on Mars that the Phoenix uncovered. If you'll remember, the little scooper couldn't dig into it; yet nevertheless, it was able to obtain some scrapings, indicating that the stuff is somewhat friable. Remember that a Mohs hardness of 6 or 7 in itself doesn't mean you need diamond saws to get at it. After all, quartz sand has a Mohs hardness of 7, yet you can excavate it with your bare hands--and it's easy to shatter diamonds with a handheld hammer. The key question is how friable ("the ability of a solid substance to be reduced to smaller pieces with little effort") it is.So a worst-case scenario is that excavating the ice will be like tearing up an old concrete highway. This is a good analogy actually because a highway comes in layers. The ice in these craters will probably be layers separated by thin layers of regolith scattered by nearby meteor impacts. The first instinct should not be to try and invent some new kind of wheel. In order to avoid analysis paralysis, the first assumption should be that lunar ice won't be any harder to excavate than similar deposits on Earth. Yes, I know its 33 K. But that in itself doesn't logically entail that off-the-shelf excavation equipment couldn't be used to a large extent. E.g., check out out these hydraulic jack hammer/breakers manufactured by http://www.poqutec.com/. Once the hydraulic jack hammer breaks up the ice into big chunks, then scoop up the chunks using a 1 yard loader bucket. Then dump the chunks into the "Jaw Crusher", which will break it into gravel sized chunks which are then fed into a tank which is then sealed. Heating elements will then melt the ice, and as the tank becomes pressurized the water will enter the liquid phase. From there, it is pumped out and filtered into the water cracking unit to be converted into H2 and O2.
In other words, don't let JPL get a hold of this problem. They will invent some sort of monstrosity like ATHLETE to do a simple job. And don't worry about mass. Weight isn't a problem. We will want weight. As long as the backhoe mass is less than 15 tons, we're golden.
How brittle are the jack hammer chisels at a few degrees above zero? Same for loader bucket, jaw crusher etc.
We can hope the lunar ice is friable. But counting on that seems a sure way to invoke Murphy's Law.
What do the boys at ULA say?
They endorse your plan to buy Caterpillar heavy equipment off the shelf and slapping them under Atlas fairings?
Ice can be cut with a hot wire. with a triple point of 273.16 K or 0.01 °C the wire does not have to be very hot.
The wheels and cutting edge of the vehicle will have to be protected against the very low temperatures.
Quote from: Hop DavidHow brittle are the jack hammer chisels at a few degrees above zero? Same for loader bucket, jaw crusher etc.I don't know. I figure it probably depends on the material they're made out of.
QuoteWe can hope the lunar ice is friable. But counting on that seems a sure way to invoke Murphy's Law.Pure FUD. People used to be afraid that Neil Armstrong was going to sink out of sight as soon as he set foot on all that dust.
Quote from: Warren Platts on 06/22/2010 07:35 amQuoteWhat do the boys at ULA say? You'll have to ask them.
QuoteWhat do the boys at ULA say? You'll have to ask them.
QuoteThey endorse your plan to buy Caterpillar heavy equipment off the shelf and slapping them under Atlas fairings?Gee, I forgot for a minute that diesel engines don't work in a vacuum, so probably not....ETA: Rocket engineers are the wrong people to talk to anyway. This is a job for Halliburton.
Quote from: A_M_Swallow on 06/22/2010 12:45 amIce can be cut with a hot wire. with a triple point of 273.16 K or 0.01 °C the wire does not have to be very hot.A hot wire won't work because of the tendency of ice to mend itself.
QuoteThe wheels and cutting edge of the vehicle will have to be protected against the very low temperatures.This would seem to be the case, intuitively. But people used to think that we would need special technology to deal with the loose lunar dust. It turned out that regular boots and tires work just fine. How do we know for sure that regular bulldozer or snowcat treads won't work? There is no need to solve problems that don't exist. Let's wait to find out if there will be a problem before we devise a solution to that problem.
Quote from: Warren Platts on 06/22/2010 07:35 amQuote from: Hop DavidHow brittle are the jack hammer chisels at a few degrees above zero? Same for loader bucket, jaw crusher etc.I don't know. I figure it probably depends on the material they're made out of.In other words, you have no idea if they'd work or not.
Quote from: Warren Platts on 06/22/2010 07:35 amQuoteWe can hope the lunar ice is friable. But counting on that seems a sure way to invoke Murphy's Law.Pure FUD. People used to be afraid that Neil Armstrong was going to sink out of sight as soon as he set foot on all that dust.OK, so Neil Armstrong didn't sink in dust. So it follows that lunar ice is sure to be friable?
Quote from: Warren Platts on 06/22/2010 07:35 amQuote from: Warren Platts on 06/22/2010 07:35 amQuoteWhat do the boys at ULA say? You'll have to ask them.I thought it was all worked out that ISRU would cut the cost of the ULA architecture in half.
1. Have you given any serious thought to lunar ice ISRU? 2. Has ULA? 3. When you flesh in some of the details and run demo models, you'll be more credible.
In the mean time I'll regard your 3.5 billion a year for a lunar base as wishful thinking.
Quote from: Warren Platts on 06/22/2010 07:35 amQuoteThey endorse your plan to buy Caterpillar heavy equipment off the shelf and slapping them under Atlas fairings?Gee, I forgot for a minute that diesel engines don't work in a vacuum, so probably not....ETA: Rocket engineers are the wrong people to talk to anyway. This is a job for Halliburton. Wasn't Halliburton one of British Petroleum's subcontractors? I guess BP demonstrates anxieties over Murphy's Law is pure FUD
(whatever that means)
So you would launch an expensive piece of equipment up without researching effects of cold? And if it breaks just shrug your shoulders and say "oh well!"?
This sounds like a recipe for cost over runs.
Quote from: agman25 on 06/21/2010 06:33 pmOne approach could be to melt the ice in place and suck out the resulting water. The ice will have to be melted anyway at some point if one has to use it.In a vacuum ice will sublimate rather than melt.A vacuum cleaner or other sucking devices rely on air and wouldn't work in lunar vacuum.
What do the boys at ULA say? They endorse your plan to buy Caterpillar heavy equipment off the shelf and slapping them under Atlas fairings?
The first instinct should not be to try and invent some new kind of wheel. In order to avoid analysis paralysis, the first assumption should be that lunar ice won't be any harder to excavate than similar deposits on Earth. Yes, I know its 33 K. But that in itself doesn't logically entail that off-the-shelf excavation equipment couldn't be used to a large extent. E.g., check out out these hydraulic jack hammer/breakers manufactured by http://www.poqutec.com/.
Quote from: Warren Platts on 06/21/2010 06:29 pmThe first instinct should not be to try and invent some new kind of wheel. In order to avoid analysis paralysis, the first assumption should be that lunar ice won't be any harder to excavate than similar deposits on Earth. Yes, I know its 33 K. But that in itself doesn't logically entail that off-the-shelf excavation equipment couldn't be used to a large extent. E.g., check out out these hydraulic jack hammer/breakers manufactured by http://www.poqutec.com/. Besides the 33K thing, another issue to keep in mind is the low lunar gravity. Jackhammers (and just about any other terrestrial digging apparatus I can think of) rely on gravity to function. It'd be bad if an astronaut wielding a jackhammer accidentally launched into lunar orbit with it.
Forget it. It's not worth it. [...] the $2 billion that it would take [...] is better off just folded into the manned program. We're going there anyway. Better to let the trained geologists figure it out once they get there.