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Rocket Mining System Could Blast Ice from Lunar Craters
A mix of dust, rocks, and significant concentrations of water ice can be found inside permanently shaded lunar craters at the Moon's south pole. If that water ice can be extracted, it can be turned into breathable oxygen, rocket fuel, or water for thirsty astronauts. The extraction and purification of this dirty lunar ice is not an easy problem, and NASA is interested in creative solutions that can scale. The agency has launched a competition to solve this lunar ice mining challenge, and one of competitors thinks they can do it with a big robot, some powerful vacuums, and a rocket engine used like a drilling system. (It's what they call, brace yourself, their Resource Ore Concentrator using Kinetic Energy Targeted Mining—ROCKET M.)
This method disrupts lunar soil with a series of rocket plumes that fluidize ice regolith by exposing it to direct convective heating. It utilizes a 100 lbf rocket engine under a pressurized dome to enable deep cratering more than 2 meters below the lunar surface. During this process, ejecta from multiple rocket firings blasts up into the dome and gets funneled through a vacuum-like system that separates ice particles from the remaining dust and transports it into storage containers.
Unlike traditional mechanical excavators, the rocket mining approach would allow us to access frozen volatiles around boulders, breccia, basalt, and other obstacles. And most importantly, it's scalable and cost effective. Our system doesn't require heavy machinery or ongoing maintenance. The stored water can be electrolyzed as needed into oxygen and hydrogen utilizing solar energy to continue powering the rocket engine for more than 5 years of water excavation! This system would also allow us to rapidly excavate desiccated regolith layers that can be collected and used to develop additively manufactured structures.
[...] The Phase 1 winners are scheduled to be announced on August 13.
(Score: 1, Interesting) by Anonymous Coward on Saturday June 19 2021, @02:19PM (4 children)
There's definitely nothing simpler or lower maintenance than rocket engines!
Leaving aside the general uselessness of trying to establish a moon colony, it's probably not worth extracting the water unless it's right there on the surface or just below. Moon regolith contains lots of oxygen. It's not much harder to extract the oxygen from the dirt than from the water, and if you're mining you are going to be producing it as a byproduct. (And if you aren't mining, what are you even doing there?)
Just ship methane up from Earth, combine with the Lunar oxygen, make whatever you need. These rockets are already powered by methane, so it's what they're already planning! There's just a much better way to do it!
(Score: 2) by Immerman on Saturday June 19 2021, @06:39PM (3 children)
I agree with everything else, but I get the feeling you're being sarcastic with
>There's definitely nothing simpler or lower maintenance than rocket engines!
And for certain kinds of engines that's actually true. Specifically solid rocket engines, which are pretty much just a rod of highly flammable fuel and oxidizer enclosed in a tube that can survive the stress, possibly with a rocket nozzle and bell to optimize the thrust generated. That basic technology spans everything from bottle rockets to model rocketry, to the solid boosters on the Space Shuttle (and many other orbital rockets)
There's also solid-gas rockets that (typically) use a solid fuel and gaseous (or liquid) oxygen as the oxidizer to allow them to be throttled, shut down, and re-started. At the simplest you can simply bore a hole through your fuel rod and pump oxygen through it. There's some very cool videos on Youtube of such a thing done with clear nylon rod operating as both the fuel and containment vessel so that you can see the flame consuming it from the inside.
Even fully liquid or gas rockets don't have to be significantly more complex, as hobbyist rocket engines around the world prove. Something like a SpaceX Raptor certainly is - but that's because they're chasing extremely high thrust-to-weight engines and extremely high specific impulse, which are absolutely essential for reaching Earth orbit with any semblance of efficiency, but unnecessary if you're only looking to produce a jet of hot gas for excavation purposes.
(Score: 0) by Anonymous Coward on Saturday June 19 2021, @08:36PM (2 children)
Fair enough. But from the summary, they're planning to split (some of) the water and use the resulting hydrogen as fuel. A fully restartable hydrogen fueled engine is definitely not on the simple end of the continuum, especially since it's supposed to blast a bunch of notoriously abrasive moon dirt all around itself.
The fact that it's a low thrust engine that has moderate mass constraints (you still have to ship it from Earth, but it doesn't have to lift itself) probably helps, but it still seems like a long shot.
(Score: 2) by Immerman on Sunday June 20 2021, @03:05AM
At the simplest end, that's still just a matter of combining pre-pressurized hydrogen and oxygen in an ignition chamber (probably with a rocket bell). Doesn't have to be significantly more complicated than a propane grill, with no moving parts except the valves... which don't actually have to be anywhere near the engine.
(Score: 2) by deimtee on Sunday June 20 2021, @04:35AM
Got to agree with Immerman here. Rockets are difficult because you need extreme precision to get high Isp.
Hydrogen is difficult to handle because they store it as a liquid at just a few kelvin.
Neither is true for the 'rocket' excavator. It's really just a big blowtorch and there is no reason you can't store the hydrogen as a gas in a big dumb tank and run a hose to your 'rocket'.
No problem is insoluble, but at Ksp = 2.943×10−25 Mercury Sulphide comes close.