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Mars Skyhook


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Initial post: Sep 26, 2010 2:25:52 PM PDT
I believe it is possible to make a skyhook (aka space elevator) on Mars out of Martian materials. it would require about 310,000 metric tons of kevlar. and be able to lift 60 metric tons.

The device would be able to launch this mass in an Earth Hohmann transfer orbit with minimal rocket power for manuvering and to enter an Earth capture orbit.

Posted on Sep 26, 2010 7:25:10 PM PDT
D. Colasante says:
Should we try our moon first?

In reply to an earlier post on Sep 26, 2010 7:34:57 PM PDT
The moon has no resources that carbon based life forms made mostly of water would be interested in.

Kevlar is mostly Carbon, hydrogen and nitrogen; all of which are rare on the moon but but plentyful on Mars. Building a kevlar space elevator on the moon means you'll have to bring all the 310,000 metric tonnes up from earth, which would be very expensive.

Also, being carbon based life forms made mostly of water, it is not a very good choice to try and colonize a moon with very little carbon and water. Mars has both. What good would a space elevator do if you had to haul up most of the material from earth anyway? And a space elevator on earth is still totally unfeasable (unless carbon nanotubes pan out...)

Given that the delta V to mars is a little less than it is to the moon, Mars would be the better choice.

Posted on Sep 26, 2010 8:21:51 PM PDT
Actually, in the book Red Mars, they push a carbonaceous asteroid into Mars orbit, fix a nuclear plant to it, and spin out the thread until it touches down on Mars and gets anchored there. It seems to me to make more sense using some space rock instead of hauling it all into orbit. Of course, that assumes you have a good mining and industrial capability in space.

And they also use the argument that whichever company builds it will then be able to use that expertise for a future Earth version.

Posted on Sep 27, 2010 1:07:57 AM PDT
of course in that same book (or a sequel) that space elevator gets destroyed and crashes to the surface, causing massive devestation.
But I agree, it makes far more sense to send the cable down from orbit than to try to lift it from the surface. Energy needed is far less, logistics should be easier as well (though keeping it go down straight might be a problem, maybe it should be built in orbit and only dropped when completed rather than letting it simply reel out as it is built as done in the book).

In reply to an earlier post on Sep 27, 2010 3:35:25 AM PDT
An interesting idea.... I assume the book was using carbon nanotubes and not kevlar, as they would lack the hydrogen and nitrogen necessary to make Kevlar on an asteroid.

Posted on Sep 27, 2010 7:10:14 AM PDT
yes, nanotubes were all the rage at the time the book was written, the future tech that promised to solve all mankind's problems :)
So they're everywhere, just like nuclear power in SciFi from the 1950s.

Posted on Sep 27, 2010 7:44:41 AM PDT
I did the calculations with carbon nanotubes, and you could build an earth space elevator with them. It is just that you need a lot longer tubes than just a few mm.

Posted on Sep 27, 2010 7:45:24 AM PDT
D. Colasante says:
So, hauling an asteroid/comet to lunar orbit might work too. No atmospheric disturbances, less gravity (less fiber needed), water at poles and/or in comet. Easier to run home in emergencies. Too soon to write off moon as uninteresting. Think tourism without the 9 month (each way) transport.

In reply to an earlier post on Sep 27, 2010 10:13:03 AM PDT
I've not run the calculations on the Moon; one large negative for the moon is that it has a much larger rotational period, about 27 times longer than that of Mars. I'll have to check if that results in less or more material for a lunar space elevator.

My point, though, was that a human colony would be possible on Mars and you'd have a reason for having a space elevator there; if there is no colony on the moon due to lack of water and carbon, then there is no need for a lunar space elevator.

Posted on Sep 27, 2010 8:38:29 PM PDT
D. Colasante says:
Well, Mars is eventually going to be in the cross hairs but it still seems so far off. I wonder if a space elevator needs to go all the way down to the surface. Space planes will be here in the near term but only to low earth orbit and for short time periods. But it might be enough to dock with an elevator connected to a station/hotel in a higher orbit. It might be a way to practice the technology and still avoid a lot of weight and atmospheric stresses (wind, rain, ice, ash, oxygen, lightning) on the cable.

Posted on Sep 28, 2010 1:43:27 AM PDT
For the moon, an EM rail gun might be better to launch things from the surface.
As you say, permanent habitation is harder, will be more limited (maybe some mining crews and factory workers), so it'll be mostly cargo pods. Shooting those into high G orbital trajectories is less of a problem than it would be with living humans.

An SSTO to LEO combined with an elevator from their to GEO might be an interesting interim solution, but only that.
Even an SSTO is a relatively expensive way to reach orbit, and wouldn't likely be economical in the long run.
Using it as a means to transport crews to the construction site of the elevator of course is the only way to get the first one of those on the ground (not off the ground, obviously :) ).

In reply to an earlier post on Sep 28, 2010 2:24:00 AM PDT
Although I agree that Mars has any advantages over the moon, I have to question this, "a moon with very little carbon and water". Compared to Earth, true. Compared to the needs of any remotely practical space colony, the moon is now known to have more than sufficient water and simply thinking about its sources and how and where it has persisted leads me to think that a fair amount of carbon is likely close at hand as well.

Again, I agree with your conclusion; just insisting upon accuracy.

In reply to an earlier post on Sep 28, 2010 5:47:19 AM PDT
There was an article on a space elevator in Islands in the Sky: Bold New Ideas for Colonizing Space that didn't reach all the way down. The trade off is that you need a supersonic transport to catch the space elevator as it passes by.

I suppose that sounds trivial, when compared to the problem of actually building such a beast.

Posted on Sep 29, 2010 7:08:11 PM PDT
I believe that a space elevator that doesn't reach the ground is called a 'sky hook'. It usually gets mentioned as a good way to catch and slow down incoming craft from space, and vice versa boosting craft into a higher orbit or flinging it into space. I wonder how much delta V is needed? I'd hate to imagine trying to hook up to something going 1,000mph faster than you are.

Oh, and the space elevator being sabotaged and crashing into Mars was my favorite part of the story.

Posted on Sep 30, 2010 5:36:42 AM PDT
To go from the ground to LEO requires a delta V of about 9 km/s to 10 km/s. The idea of a skyhook is to use the earth's rotational energy to get most of that kinetic energy. The G*M_earth*m_payload*(1/r_orbit - 1/r_surface) potential energy that you must overcome by climbing the skyhook is small in comparison.

Posted on Dec 24, 2012 10:47:08 PM PST
Ehkzu says:
An Earth space elevator would require materials technology we don't have and don't know is possible. Conceivably you could build one up from the Andes on the equator, but it still would require new materials.

A problem not mentioned thus far is that a space elevator would need to be able to dodge satellites and space junk in orbit around the planet/moon in question. That would be a really big problem with Earth. But even Mars is liable to have a number of satellites that we put there.
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This discussion

Discussion in:  Science forum
Participants:  6
Total posts:  17
Initial post:  Sep 26, 2010
Latest post:  Dec 24, 2012

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