This Is Not Your Grandfather's Moon
Let the moon rush begin, op ed, Homer Hickam, Washington Post
“As these efforts get going, however, it’s important to avoid the thinking of a half-century ago and look at the moon in a different way. This is, after all, not your grandfather’s moon. After the Apollo moon-landing program of the 1960s and ’70s, a series of robotic missions discovered that Luna was a lot more interesting than many had previously thought. It has abundant water and oxygen, as well as helium, platinum, thorium, rare earth metals and other minerals that may well be worth digging up and transporting back for use in thousands of products.”
Great Op-Ed with strong reasons for a lunar return.
I like Mr. Hickam, and I agree with most of what he’s said here. However, NASA’s efforts continue to be joined at the hip with that sinking ship Boeing and for “Professional Astronauts” to really land on the Moon first like he says, SLS first launch needs to stop slipping. I just read that it’s been kicked back yet again…this time to April 2021.
I don’t know how SpaceX can land a ship the size of Starship on the Moon without sending a ton of dust and gravel into permanent orbit…but I do know that they will think of a way and are moving with fully funded efforts and thanks to politics NASA is not. Money is king.
I’m not sure how landing a Starship could send dust or gravel into a permanent orbit. Maybe a whole lot into suborbital trajectories, but an orbit is a closed path. If it started on the surface, it’s going to reimpact within one orbit. For very small dust, you can play games with static electric charge, and a Starship would definitely have a huge impact on the lunar atmosphere. But I don’t see an orbital debris hazard.
Ok, well its something that I read some people smarter than me speculating about somewhere.
As I said, I don’t see it. But I just did a related calculation. The so-called “lunar atmosphere” has a total mass of about 10 tonnes. Getting one Starship, fully fueled at launch, to lunar escape velocity will put out 1100 tonnes of exhaust. If you only launch with enough fuel to get to escape velocity, that’s “only” a bit over 100 tonnes.
I’m not sure how long that would stick around, but that might cause legal problems. It would have a global impact and preclude studies of the lunar atmosphere. Is that violating the non-interference clauses of the Outer Space Treaty?
The question is how far will the exhaust would go. Also how does that compare with the exhaust from the LEM?
As a side note, wouldn’t it be great if an electrical field could be used to channel that exhaust to a cold trap created at a lunar spaceport? Could be a good source of Carbon, Hydrogen and Nitrogen.
The LEM put out about 10 tonnes during both landing and ascent. Starship would be about ten to a hundred times more, just for takeoff.
I suspect the effects would be global. This sort of things has been modeled, but not quite for this application. Usually, the studies are about what happens to water from a comet impacting the Moon, or things like that. It’s basically about individual molecules hopping around randomly. A molecule hits the surface, sticks for a time which depends on the surface temperature, then flies off with a velocity which also depends on the surface temperature, and takes a ballistic hop in a random direction. I think a typical hop would be about 100 km, and then the whole stick-release-hop process repeats. Unless the molecule is broken up by UV photons or diffuses into rather than out of the surface. But given the quantity of gas involved compared to that of the lunar atmosphere, that random walk is going to take exhaust all around the Moon. If someone wants a more detailed answer, I’m a little short of grant money at the moment, and “will model exospheres for food.”
The other question is whether anyone would actually care. The natural atmosphere of the Moon is about as dense as the Earth’s atmosphere at the altitude of ISS. Even increasing it by a factor of a thousand might not affect anything other than scientific studies of the lunar exosphere. Although I wouldn’t rule out condensing out on things like farside telescope mirrors (especially if they are IR telescopes with cooled mirrors.)
In terms of cold trapping it near the source, that’s not a bad idea, but I don’t know if it’s practical. Almost all of the molecular would be neutral, so guiding them with electric fields wouldn’t work. A trench, with the bottom in permanent shadow, would collect some of the exhaust. But to collect a significant fraction, you might need an impractical amount of trench work. Much (most?) of it would, just naturally, eventually end up cold trapped in polar, permanently shadowed craters. That’s extractable and reusable.
Guess there is really no choice. Either one Starship with 100 tons of cargo or a dozen Blue Moon landers, the numbers per kilogram will be the same. The alternative of waiting until we have antigravity is just not practical.?
That’s not obvious (well, the part about antigravity is…) At the very least, this could employ some lawyers and create precedents on what “interference” in the Outer Space Treaty means. And someone may have to spend the time and money required to write an environmental impact statement.
On a practical side, the astronomers might want to know if their far side telescopes need decontamination heaters. As you noted, recovering the exhaust would provide useful resources. Depending on the details, that could be easier or harder.
Since the transport process is very dependent on the surface temperature, that means this could be a factor in site selection (less sunlight immediately poleward of a cliff or mountain) or schedule (a landing around dawn instead of noon.) Since it also depends on the molecular mass of the exhaust and how volatile it is, it might be a factor in fuel choices (hydrogen versus methane). And, as far as Starship versus Blue Moon (I wish they had called it New Armstrong…), when it comes to recovering the material before it spreads around the Moon, there might be a difference between an occasional big landing versus many small but more frequent ones.
This isn’t really any different from other human activities. They all affect the natural environment to some extent. It’s a matter of figuring out what the impact is, how to mitigate it or keep it to an acceptable level, and especially finding ways to do so which aren’t prohibitive. Sometimes, an almost trivial difference in the way you do something can have a huge effect on the environmental impact.
New Armstrong was suppose to be Blue Origin’s follow on rocket to New Glenn, but I haven’t heard anything about it in a while. Sadly it looks like Blue Origin is falling into the Old Space pattern of doing things that NASA wants instead of moving beyond NASA like SpaceX is striving to do.
“Will model exospheres for food,” LOL. I don’t have any grant money to dole out, but at least I know where to go if it becomes available 😉
Interesting aspects of returning to the moon these days dealing with topics such as changing the lunar atmosphere. I wonder what other such topics will be brought up as now we’re about to get real spaceships going there.
It’s worth mentioning that one Apollo-era scientist almost made an embarrassing mistake. The data from his instrument in the Apollo Lunar Surface Experiments Package was detecting a transient atmosphere of water vapor and hydrocarbons. It would appear for a short while, and then disappear. He nearly held a press conference to announce such a surprising discover. Then he realized it happened when the astronauts were venting waster water from the LM.
They are claiming escape velocity is possible.
https://www.theverge.com/pl…
Well, that’s in the comments not the article itself, and there doesn’t seem to be much of a consensus among the commenters.
In any case, escape velocity isn’t a problem. Any particles ejected at that speed will go away and not come back. Space really is big. Orbital debris is only a problem when the junk is confined to a relatively small region of space (like low lunar orbit). But for a landing or launch, it’s either going to leave the system or reimpact. It’s not going to go into a low lunar orbit and stay there. It would probably sandblast anything nearby, but I don’t see how it could create a debris cloud in lunar orbit.
You seemed to be sceptical that the dust would obtain orbital velocity. Well if some of the dust could obtain escape velocity ( and there is no analysis in the article) then I would think it would be logical to assume that the spectrum of ejecta velocities would include orbital velocity. I think you are right that the amount ejected to orbit should be limited. I thought the whole issue was interesting. It certainly wasn’t something I had heard of before. I hope there is not enough crap ( to use a highly technical term) kicked up to get up into the injector of an ascent engine like Starship that isn’t protected by a second stage.
I think what frary is pointing out it that for a particle ejected from the surface of the moon, you really have two outcomes: [1] ballistic trajectory and re-impact on the surface, [2] escape velocity and it never returns. It would seem that to impart velocity that would place the particle in a circular or elliptical trajectory around the moon, you’d need a means of adding the velocity component after it was ejected from the surface (not unlike how a launch vehicle redirects part of the delta V into achieving the desired orbit). I suppose some of the ejecta from shortly after lift off could be impacted by additional rocket exhaust and thereby obtain the energy/velocity needed to stay in orbit.
Exactly. Elliptical orbits are closed paths. Initially the particles would be at the surface and moving upward. Even if they have orbital velocity, there will inevitably be a point somewhere else along the orbit where it is at the surface and moving down. At that point, it hits the surface and stops.
To get it into orbit, and one that doesn’t impact within one orbital period, something would have to alter its orbit and raise periapsis above the surface. Photon pressure could do that. Static charging and electric fields could do that. But only for very small particles (probably smaller than a micron.) I don’t think further interaction with the plume would do it. The exhaust is moving downward, which is pushing the debris in the wrong (or right…) direction. It would be the back blast from the plume hitting the surface which is lofting debris, and that’s only present when the rocket is close to the surface.
So I’d say this is a real and serious issue near the landing and launch site, and potentially a foreign object damage issue for the rocket itself. But I don’t see it producing a long term orbital debris hazard. I’d expect it all to settle out in an orbital period (call it a couple hours.)
Seems like if we have enough traffic arriving and leaving the Moon that kicked up dust is an issue, we could just build a dedicated launch and landing pad so that exhaust has minimal interaction with lunar dust. Hmmm, how to get all those bags of Quikrete up there…;-)
PISCES at UHH is on it, using lunar materials. They already made some demonstration titles using NASA funding they showed videos of at the American Society of Civil Engineering conferences. Actually if you don’t attend them you would be amazed at how much research has already been done on lunar construction and mining using robotics systems.
Good to hear and not surprising, if you think about it. Now, if they, or one of their competitors can get a contract to actually try it out on the Moon as part of the activities when we do finally return, that would be cool!
I’ve seen some interesting proposals with either solar-powered laser-sintering or just using large mirrors / lenses to focus raw sunlight to melt regolith into a cement-like roadways and building blocks.
Since starship is mentioned. Anything left on the moon for use afterwards with starship would have to be placed away at a safe distance. Safe from possible debris field and such.
Or close by but underground. That might be advisable anyway, to protect facilities from meteorites and radiation.
Close by underground could take a lot of time to set up. Time not plausible for a crew to spend the time working on. Then moving into. It would take a lot of extra resources also. Possibly if a lava tube is used then maybe. A decent habitat could be moved away from the ship and covered over with lunar soil relatively fast. More layers added up over time. Then more elaborate underground structures afterwards could be built once established. Underground with rockets going off near by could risk collapsing. Habs covered over with soil allows it to protected, and easily repairable if needed. Land habs have the benefit of being placed where you want them to be. Drilled and blasting a basic shallow cave into the base of a mountain for a hab could be possible option to.