Screw the Space Elevator, Lets Launch Loop

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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MSimon
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Postby MSimon » Fri Apr 11, 2008 5:48 pm

drmike wrote:Using pressure to measure tensile strength is weird, but it makes sense. So it is possible in theory any way.

I do like the Aerovator. Seems much easier to build. But I suspect it will have to get in the way of some airline and bird migration paths.

but in both cases dealing with how to maintain things and replace worn parts seems like a major problem. You'd have to have something mounted on the cable/ribbon holding the whole system and put in a repair in the middle.

Neat ideas to think about in any case!


I never thought anything of it because I have been using psi for decades to to do strength calculations. Figure the force involved. Find the psi of the material. Figure the area * safety factor.

BTW Young's modulus is in the same units psi or GPa.
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TallDave
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Postby TallDave » Fri Apr 11, 2008 9:08 pm

The difficulty is that the required strength is at the material limit.


Yeah, if you read through the challenges, there are many many issues that would need to be solved. Launch loop does look like it might be more viable.

Mike Holmes
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Postby Mike Holmes » Tue Jun 10, 2008 6:01 pm

Hey, fusion power could get us into space cheap, making it easy to make that orbiting station which we'd use to make cheap launches...

Oh... wait... that'd make it redundant at that point, wouldn't it?

Fusion doesn't "cut both ways" it simply leapfrogs technologies that people envision as neccessary because fusion power isn't available. Space elevators and such really only are solutions to the problem of expensive chemical propulsion; once you have fusion, the need for this goes away.

Mike

Nydoc
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Postby Nydoc » Sat Nov 01, 2008 11:50 pm

Hi. I just recently stumbled across this forum. Looks like there's a lot of cool ideas here.

MSimon wrote:The estimated strength rqmt is at 65 GPa. The best carbon nanotubes (CNT) we can make are right in that range.

Ultimate strength estimates for CNT are in the 120 GPa range with diamond a little better.

Obviously we need to reliably make CNTs in the 90 to 100 GPa range to give a safety factor of 1.5 (aerospace minimums).

The fact that a loop launcher can be made with ordinary steel is a big plus.

A 65 GPa tether is the requirement for an SE to be economically feasible. SEs could be physically feasible with much lower GPa. As someone pointed out earlier, you could build an SE with steel (1-2 GPa) but it would be about a mile wide in the middle. Individual CNT strands have been tested at 60+ GPa. The tether would not require continuous molecules traversing it's entire length. Rather, it would be constructed of threads made from much shorter strands of CNT twisted together. The current maximum length for CNTs is a few cm and this would be suitable.

I think the Aerovator is a much better option than the SE, and safer and less complicated than a Lofstrom Loop. It only requires 6-10 GPa and is easier to build and maintain. However, it hasn't gained much traction due a lack of professional studies. I am curious to know if spinning the Aerovator through the earth's magnetic field would cause problems or if it could provide a power benefit.

KitemanSA
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Postby KitemanSA » Sun Nov 02, 2008 3:01 pm

Hi folks,

The launch loop is one alternative to the space elevator. There are a number of others. See:

http://en.wikipedia.org/wiki/Non-rocket_spacelaunch

The two that interest me most for orbital insertion are the HASTOL and the hypersonic skyhook. In each case, a ready supply of HV power would be marvelous. Ultra High Isp thrusters could efficiently store momentum for rapid deposition into payloads.

Yes, there are jet planes now, but there are also cargo ships. Both use petroleum distillates for energy. One technique for using them does not preclude others. One fusion transport will not preclude others either.

Heck, even a space elevator will need MASSIVE amounts of energy!

Nydoc
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Postby Nydoc » Sat Nov 22, 2008 9:41 am

Nydoc wrote:I think the Aerovator is a much better option

I take that back. It would never work for a myriad of reasons.

KitemanSA
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Postby KitemanSA » Sat Nov 22, 2008 2:57 pm

Nydoc wrote:
Nydoc wrote:I think the Aerovator is a much better option

I take that back. It would never work for a myriad of reasons.


Good on ya, mate! I was about to rip you... unh politely disagree.

The most do-able low cost system today IMHO, (with current commercially available materials) would be a three stage system of a KITE launcher, rocket, and HASTOL. As tether materials get stronger, the rocket could be dropped.
Each of these items can be seen in:
http://en.wikipedia.org/wiki/Non-rocket_spacelaunch

The KITE takes you to ~M6 and ~70km altitude. The rocket then takes you to M15 & around 150km altitude. The HASTOL takes you the rest of the way. In each step, the selected process provides low units of the specific velocity of the primary material, the tether material for the KITE and HASTOL, and the exhaust velocity for the rocket. It is only when you go above the specific velocity does the exponential nature of ALL the relevant equations bite you, so keeping in the low units assure maximum efficiency.

kunkmiester
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Postby kunkmiester » Tue Jun 09, 2009 2:50 am

How's about something like this:
http://autogeny.org/tower/tower.html
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