Rocket Propellant from Lunar Soil | Hacker News Reader

Rocket Propellant from Lunar Soil

wickmanspacecraft.com

72 pointsvpribish42 comments

I feel like the difficulty of obtaining rocket fuel on a given rocky planet is equivalent to within the limits of napkin math. I've never heard a particularly convincing argument for using the Moon as a springboard to the wider universe as opposed to Mars or Venus. Perhaps someone could offer some correction.

Not a rocket scientist, nor do I have any hard numbers, but off the top of my head the Moon has a much smaller gravity well than Mars or Venus. On Mars, you would waste much more fuel just getting back into orbit. And Venus is just comically toxic. We weren't even able to build a single probe that lasted more than a couple hours on the surface of Venus before corroding, much less a permanent settlement.

Also, the moon is only a few days of travel away, instead of months-to-years (so someone on a permanent base could be medically evacuated if they have a tricky tumor, say.)

The Moon's gravity well is smaller but, with no atmosphere, it's both much easier to escape, and much harder to land softly on. If anything, I'd guess our best bet is a propellant factory on the Moon, using a magnetic launcher to shoot the fuel into lunar orbit to supply an orbiting fuel station.

Giving the moon magnetic catapults is giving the moon weapons for their eventual war for freedom from earth.

TANSTAAFL!

Silence, Comrad - you will blow our cell! Or are you working for Warden - Catapulthead-svinoi!

Magnetic launchers can be used in reverse as catchers too as a sort of atmosphere replacement.

How so? Would you have to "land" by going back down the barrel of the launch device?

That'd be quite a trick if you could pull it off - the precision required seems formidable, though.

Like trying to land a rocket upright back on its launchpad. Lunacy.

The rocket gets to 'fly' in, taking advantage of the atmosphere for control and braking. Not that it's not a bonkers achievement but the speeds are much higher and the tolerances much lower to slot an orbiting payload back into a linear rail.

Magnetic Lander might be a decent smartphone game...

How is that that much different than landing on an aircraft carrier?

Should be easier if we can assume that the vehicle is powered because the landing stage is not moving.

It's occuring at orbital velocity in a vacuum.

Would the vacuum piece make it much easier than landing on a carrier

At least there wouldn't be a crosswind

How about a space elevator?

Actually can be built with existing materials I remember reading

Unfortunately the moon turns very slowly. It is tidally locked to Earth. The cable of a moon space elevator would have to be the length of the moon-earth distance.

You should look up proposals for Venusian cloud cities. In many senses Venus is more hospitable than Mars.

On Mars, or on Moon, you have a lot of local materials to build from. A Venusean floating city needs to be brought in completely from the outside.

I can see how you might think that, I suppose, but you do actually have an entire planet full of useful resources at hand, even if they're not ones that you might immediately think of. There are many things that you can reasonably extract or synthesize from the Venusian atmosphere, particularly plastics. This StackExchange answer has more details: https://space.stackexchange.com/questions/9158/what-useful-m...

The lower gravity and lack of oxygen make launching things with maglev sleds into orbit feasible. There have been a number of studies of a launch rail with a reusable 'bucket' carrier that would be built along an incline for a suitable orbit. The bucket would be accelerated electromagnetically along the rail, imparting sufficient energy to put the contents of the bucket into orbit which would be circularized at apogee with a small rocket burn. The rail would be powered by an array of solar panels and batteries, or possibly a flywheel similarly to the way the EMALS[1] system was designed.

Landing is the challenge on the moon as there isn't anything to push against or dump energy into. I don't know if anyone has considered a space elevator, I expect keeping it in position would be a challenge given the orbital dynamics involved.

[1] https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launc...

Not only have people considered a lunar space elevator, but, you can actually build it with today's materials science: https://en.wikipedia.org/wiki/Lunar_space_elevator

You could create a semi atmosphere- by Electrically Blowing Up Sand? Sort of like simulating Atmosphere with a shotgun blast?

If you are asking whether or not you should somehow accelerate lunar regolith upward and use it to decelerate an incoming lander, then yes you probably could. Although it would no doubt cause damage to the landing craft much as an atmosphere braked entry 'burns up' the heat shield of a landing craft. Further the dust contains a lot of aluminum silica and that is essentially sand paper so you would get a lot of abrasion.

For as long as ice is present on the moon, using it is a matter of melting it, filtering, and electrolyzing.

Moon is also a sure source of aluminium. Components can be shipped flatpacked to the moon, where they will be placed on locally produced aluminium "skeleton"

I wonder if it would be feasible to build a solar furnace capable of melting aluminium with focused sunlight - the light side must have pretty steady and strong incoming solar radiation, with no atmosphere?

> I've never heard a particularly convincing argument for using the Moon as a springboard to the wider universe as opposed to Venus

The mere fact that Venus has a thick CO2 atmosphere surrounding a surface with a temperature 872°F should be more than convincing, let alone the 90 atmosphere pressure and sulfuric acid clouds and all the other icing on the cake.

You should read more about proposals for Venusian colonies before assuming that your knowledge of the subject is sufficient for discussion. No one is proposing to live on the surface, and the sulfuric acid is not a particularly large problem.

When was the last time you saw a hovering colony on Earth that now you think we could make one on Venus?

Please review the existing literature on this subject. Particularly, take note that an Earth-normal atmosphere constitutes a lifting gas on Venus. This is not the game where you utter every trivial objection that springs to mind on the basis that no one has bothered to give the subject more than five minutes' thought. Your statement about surface temp/pressure is a clear indicator that you have not bothered to research this issue in the slightest degree, and this comment is an ineffectual attempt at saving face. The people publishing papers on this topic seem to think it's reasonable. Your sarcasm and ignorance on this matter are extremely offensive.

Dude, put down your guns and chill out a bit? When you said "obtaining rocket fuel on a given rocky planet" and "springboard to the wider universe" I naturally assumed you meant launching a rocket from Venus's surface, not making a colony in the upper atmosphere. That seemed quite reasonable to me, but obviously not to you. So you replied with a snarky comment telling me to read the literature of Venusian colonies (which wasn't even the topic), and after you changed the subject, I asked what makes YOU think we could actually build one when we haven't even had anything like it on Earth. (I emphasize YOU because you had asked us to convince YOU, not some random researcher in NASA.) My comment there wasn't sarcastic; it was a completely serious comment that did consider the fact that people have been researching the idea seriously.

I stand by it: just because people are proposing the idea of a base over Venus seriously that doesn't mean much about its feasibility compared to a base on the moon, and just because one person is convinced something is possible, that doesn't mean another person will be. (As a more Earthly example of this, I might respect Elon Musk, and I know he knows what he's talking about more than I ever will, but that still doesn't mean I'm convinced the Hyperloop is as feasible as he seemed to think. I still respect the idea and will take it seriously if he does, but that doesn't mean I'm convinced by it in any way. Same here.)

Now, instead of firing all your cannons at me and flaming me, I suggest you calm down and take a walk before replying, so we can be a little more civil here. If you're already an expert on the topic, maybe explain a little more of what you already know and why you do/don't find it convincing when you're asking your question, so the rest of us plebeians have a foundation to build on that you won't find "offensive".

You admittedly lack foundational knowledge on this topic, which means you should be asking questions from the position of an open mind rather than trying to insist on the impossibility of something. Even better, you might try to pro-actively acquire some foundational knowledge.

Without having any frame of reference for your learning, and without being a true expert in these matters, this is the situation as I see it.

The Moon is close in terms of distance but not all that attractive in terms of delta-v. Mars and Venus and the Moon are all within hand-waving distance compared to the wider solar system and certainly when compared to anything more distant. Lunar regolith isn't the worst building material, but that it lacks an atmosphere is a more serious stumbling block than might be anticipated. Lunar dust does not get tumbled and so is quite sharp-edged, and liable to get into many unpleasant places. Lack of water is a concern on most places, and that two-week-long night is going to make solar power a challenge except potentially at the poles. Generally, there's not a lot there that isn't common other places, and having some sort of atmosphere tends to be useful. If the goal is to go further out, then Ceres is liable to present most of the same challenges, but without the water issue. The proximity of the Moon in terms of time is a misleading consideration. In an emergency, it's going to take a long time to get out there unless we happen to have a rocket prepped on a pad (which can be assumed not to be the case). Any disaster is liable to be over long before aid could arrive.

Mars is of course not a bad option, and we do have a better handle on how to build ground-based structures. This is the option closest to today's technology and correspondingly has been explored in much more depth. Mars has an atmosphere, more gravity, and potentially-useful ice caps. Whether or not it should be a destination seems moot at this point; we're going.

Venus however has a number of advantages. As mentioned, an Earth-normal atmosphere is a lifting gas in the Venusian atmosphere, and at 50km the temperatures and pressures are reasonably close to Earth norms. Atmosphere leaks would therefore not be catastrophic. Being closer to the Sun provides more available solar power, and being closer to Earth means more frequent launch windows. The main issue is coating the exterior with something resistant to the sulfuric acid atmosphere. As I recall, there are a number of suitable plastics which can be made more-or-less directly from the atmospheric carbon.

For more information, I would suggest browsing Wikipedia, and perhaps reading Geoffrey Landis' work on the matter. He's not the only one with sensible plans for this, and he does have some critics, but his arguments are well-informed and well-considered.

And yes, I asked people to convince me that the Moon was a better option. Generally, the people who think about these things focus on other options. I was certainly hoping for some expert opinions on the matter.

Rotating tethers ought to be practical around the moon even with current materials: https://en.m.wikipedia.org/wiki/Momentum_exchange_tether#Cis...

I found Wickman's story pretty interesting! Thanks for posting.

There was a lot of interesting info on there besides this post. Ahem -- the post itself was really interesting -- reminds me of how little I know in spite of my interest in space. Gotta get on that!

You may also find LANTR (LOX-Augmented Nuclear Thermal Rocket) interesting:

http://www.nss.org/settlement/moon/LANTR.html

LANTR is still assuming that hydrogen is supplied from earth, but it's performance as a rocket fuel is magnified by using it in a hybrid nuclear thermal/chemical rocket, where the the LOX is supplied from the moon.

"aluminum powder in gelled LOX"

Sounds interesting. I wonder if a hybrid engine would work also. i.e. solid compressed aluminium powder with LOX.

I wonder- if a planet continuously lost atmosphere of the aeons, shouldn't there be a small swirl of gas spiraling out from that planet?

If that is the case, wouldn't it be enough to have a ram-scoop satellite harvesting it?

I assume you are talking about Mars? It's not in space in isolation. Solar wind has been blasting away the atmosphere for aeons. So it's probably intermingled with solar wind across the trail of the solar system.

It's probably going to tend to collect on the heliopause, but there's a lot of surface area there.

And it's a pretty long ride out.

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