Could we get back to the moon with an elevator?
It’s certainly a lot easier problem, and one more within current tech, than one from earth. This is the kind of innovation that NASA should have been pursuing, instead of redoing Apollo.
Of course, an interesting question is how you’d get to other locales on the moon, so you’d still need a hopper of some kind (pretty much functionally equivalent to a lander, except for total impulse requirements), but if you could manufacture fuel at the base of the elevator, you could deliver it to orbit with the elevator, and to the rest of Luna with the hoppers/tankers, really opening up the whole planet, while dramatically reducing costs of operating in cis-lunar space. For example, whether it made more sense to get to the south pole by going down the elevator, and then hopping, or direct descent from the Lagrange point using lunar propellants would be a function of the relative economics and propellant prices in the two locations. These are the kinds of studies that it would be nice to see out of an architecture revisit. It begs the development of scenario simulation tools (that would make for interesting sim games for the general populace as well…).
[Update a few minutes later]
It seems entirely possible that it would be cheaper to deliver propellant from the moon to LEO via elevator/high-Isp-tanker than from the surface of the earth. That would be a real game changer, but it would wipe out much of the new market for launchers. On the other hand, in-space transportation might become so cheap that it would open up vast new markets for other things. For instance, vacation cruises to the moon become much more affordable.
[Link via Clark]
For instance, vacation cruises to the moon become much more affordable.
But only once LEO vacation cruises become affordable. Depots + exploration or something else that generates a lot of demand for launches is more important than ISRU. Something still needs to drive down the price of getting to orbit. Having said that, if somehow we can only get ISRU, that would still be great.
Depots + exploration or something else that generates a lot of demand for launches is more important than ISRU.
They’re both important. I think that propellant delivery will offer a useful market long enough to drive down launch costs before a lunar elevator undermines that market. But I also think that both can happen a lot sooner than anyone thinks once we unleash the market on the problem.
They’re both important.
Certainly, I was only arguing depots are even more important than the already quite important ISRU.
I think that propellant delivery will offer a useful market long enough to drive down launch costs before a lunar elevator undermines that market.
Likely true and a reassuring thought.
But I also think that both can happen a lot sooner than anyone thinks once we unleash the market on the problem.
And if current rumours are to be believed, unleashing market forces might happen a lot sooner than I had thought was possible. Especially under this president.
Still, they’re only rumours. Rocketman is sticking to his story, but I haven’t seen real corroboration, Keith Cowing’s anonymous source notwithstanding.
I haven’t done the research (and yes, I know I should already know this), but can you lunar elevator given the instability of lunar orbits and the large gravity gradients?
You would have to run it thru EML-1.
One minor problem — not insurmountable, but noteworthy — with building a lunar beanstalk from materials such as M5 rather than carbon nanofibers is degradation and depolymerization by solar ultraviolet. Presumably you could overcome this with a thin metallic coating on the ribbons. It can’t be too thin, though, or the solar wind and even outgassing from cargoes will eventually degrade the metal film. And when you’re talking about structures tens of thousands of kilometers in length, the mass of even a “thin” film can become non-negligible.
I’d like to see a lunar beanstalk, and I suspect that one eventually will be built, but I don’t think it wil open up the Moon to exploration. I think it will be built after the Moon has been been exploited for a while — it will help, but it won’t be a game-changer.
I suspect that for at least the next century it will be far more feasible in terms of fabricability, risk, and expense to use rockets or electromagnetic accelerators to ship things from the lunar surface to lunar orbit or to lunar L1.
Let’s dig out all those old discussions of rotating lunar skyhooks. We don’t need no unobtainium to build THEM!
Rotating skyhooks could also be useful around Mars.
Getting extra terrestrial resources to LEO really would be a major step.
At 100km/hr it would take 3.3 weeks for a climber to get to the Lagrange point. A much faster maglev climber system is really desired. On the plus side solar and even battery powered climbers should be possible. I do like a Lunar elevator far more than an Earth elevator, though the practical complexities are still considerable, not near term.
Another idea I came across recently is to use a glorified trebuchet to throw a bag of regolith above the lunar surface and then hit it with an LLO high ISP rocket vehicle with a regolith armored bucket (with a rotating valve lid) on the front. Simple! 🙂 Well a very low initial investment at least.
At 100km/hr it would take 3.3 weeks for a climber to get to the Lagrange point.
There would be no hurry for non-human cargos. And you could probably go faster — it’s just a matter of power.
I like the idea that a space elevator could be inflatable. Just make certain not to use Hydrogen as your lifting gas here on Earth.
On the Moon perhaps it would be possible to use magnetism to hold each section of the tower in place. Erect sections on the surface and just incrementally push each section upward. Levitate the sections using electromagnetism to push the tower up and attach the next section. Magnetism would hold the sections together. Magnetism could also be used to carry a ring shaped lift vehicle up and down.
A space elevator does not need to have a counterweight to function to make it work from earth to the boundaries of orbital space. Even a more traditional elevator system can be deployed by combining a carbon nanotube tether and a SpaceShaft. The SpaceShaft concept is explained at http://spaceshaft.org. Even a SpaceShaft can be used for the deployment of the CNT tether. Please note that unexplained secondary systems such as anchoring and mooring of the SpaceShaft are not discussed in detail because of patenting applications, but we are fully aware of heave, roll or heeling at atmospheric elevations. Certainly a SpaceShaft can be also used at other locations in the Solar System. Even sections of it can be redeployed from the Earth’s orbit and relocated to the Moon or Mars at a much shorter future than what is required for the currently popular system.
one more thing that will be a very important factor in the development of space elevators is not so much the promise of low cost access to a tourist destination but a low cost access to space for prospectors. If you want to know more of what I think on this issue of prospecting and space elevators read my posting at http://www.npr.org/templates/story/story.php?storyId=106304112
to Josh Reiter: indeed an inflatable is a nice idea, but good for only places where you just one a tower. The inflatable by Prof Quine is something I discarded from my inventory of ideas, (when I was trying to find a solution to the many other problems the tether based space elevator has,) because of the elevation limits it imposes. Because many people believes that such concept came before the SpaceShaft, but that is not the case, I had to contact several of the online publishers distributing the news of such a system as a novelty but the only one that did respond to my emails was “Knight Science Journalism Tracker” see http://ksjtracker.mit.edu/?p=9690 , the reason why such publishers did not respond is obvious, Prof Quine has the financial support of a university and proud Canadian government , something I don’t.
There would be no hurry for non-human cargos. And you could probably go faster — it’s just a matter of power.
Not really, mechanical contact systems do not like going that fast, maybe a 300km/hr would be possible (8 day travel time), as per some trains on Earth, but this is non trivial and would perhaps require extensive ongoing maintenance.
However from an economic perspective one can not just go slow, dry mass fractions apply to elevators just as they apply to rockets – and for slow elevators they are really, really bad. 1.2 ton payload per 6100 ton elevator once every week is never going to be cost effective compared to other technologies. And I will leave the calculation of exactly how many centuries it will take to bootstrap the counter weight as an exercise for the student.
It continues to amaze me how many otherwise highly intelligent folk do not calculate basic economics. Excepting rather rare designs/circumstances, space elevators are very obviously dumb – so many obviously dumb people???
Not really, mechanical contact systems do not like going that fast, maybe a 300km/hr would be possible (8 day travel time), as per some trains on Earth, but this is non trivial and would perhaps require extensive ongoing maintenance.
No need for contact — that’s what maglev is for, and it’s a lot easier when you don’t have to fight gravity.
1.2 ton payload per 6100 ton elevator once every week is never going to be cost effective compared to other technologies.
Why would that be the payload limit, and why would there be a counterweight?
To Pete:
Pete I get your point, however there are technological hybrids that can tackle both the journey speed and the ratios of structural mass and payload mass, also your point of an asteroid relocation can be put aside by harnessing buoyancy in a very large scale, which can provide uptrhust in thousands of tons. The problem is that no space agency truly believes in the technology as to invest on it whether is a carbon nanotubes or SpaceShafts, neither do most of the public (including you as you point out). However that attitude would drastically change if there was the urgent need to escape an asteroid impact. At the time of a catastrophic event everyone will be motivated to appoint all kinds of resources! Let me give you a couple of examples of the use of a SpaceShaft. 1) Many science balloons are fast, taking less than 1 hr to reach 50 km in altitude, (half the distance to the official boundary of space,) and their payload of up to 1/2 ton are not unheard of. Assume that a number of such balloon are made to be rigid, (such balloons are called super-pressurized,) and that there was a way to attach them one after the other making up a column. Assume that each of such balloons have a diameter of 500 meters and you divide the distance of the significantly dense atmosphere in which they can operate, i.e. 50 km, the result is 100 of those balloons multiply that by 1/2 ton each and what you get is already a distributed upthrust force of 50 tons. However keep adding more of those balloons at the base of the column! What you get then is a combined method of construction and transportation that can reach easily the boundaries of orbital space. Of course you need to have a method by which you insure that the column stays upright and not free to lay horizontally, or how to counteract jet stream (winds), but those are things I will not discuss here. For the second example I will speak about the cost of such a structure using Helium to make it work. There are other ways to make something buoyant but I will not discuss them here. To substantiate my claims visit http://topweb.gsfc.nasa.gov/balloon/why.html . But in a nutshell even if inexpensive to some people it is very expensive to an individual like me to tackle all alone such a system. Helium for a SpaceShaft with a diameter of 100 m (which is the size of a building block in most European countries) will require only 2% of yearly global production of Helium, which will make this system of transportation to space extremely accessible even when compared to the objective pursued by CNT tether systems. All in all I am not saying that it is easy, but it is certainly not impossible. We have vast understanding of buoyancy (from the time of Archimedes) and we have been building balloons for centuries, however until now nobody thought of the simple principle of a spar buoy to be applied to accessing space. So go ahead visit my website http://spaceshaft.org where there are more explanations on how such a system works (and of course you are welcome to donate $ , ( in return, if I succeed with building this thin,g I will credit your donation against a future ticket to space 🙂 )
You know “Nelson,” if you could find the return key on your computer, people might be more interested in reading your posts. Because absent that, you just look like another Internet nut.
No guarantees, but just sayin’…
No need for contact — that’s what maglev is for, and it’s a lot easier when you don’t have to fight gravity.
Fight gravity as much… Yes a non contact system is highly desirable, but the significant mass of the maglev system will need to be integrated into the elevator which will significantly reduce the effective specific strength of the tether – which leads to a much heavier tether. There are some other possibilities, but all this is even less near term technology.
Why would that be the payload limit, and why would there be a counterweight?
1.2 ton payload and 6100 ton total system mass were one set of numbers given in the Wikipedia link. Unfortunately I do not know the breakdown. I have not modeled this myself and I do not know what the payload mass fraction flow rate would exactly be.
A maglev Lunar elevator might potentially be a rare case where space elevators could add up economically. But I have not seen such numbers nor run them myself. Dry mass fraction and flight rate really matter for space elevators, just as they do for rockets, and I have seen little mention of this.
Hello Rand Simberg
Thank you for the advice I will do my best to follow it.
However sometimes, as you probably are aware of, I get these annoying messages that there are only so many characters allowed per post, so what I was trying to do is keep it as compact as possible.
I appreciate the feedback.