Manned Spaceflight Gets a Kick in the Pants (1 Viewer)

[Andrew Testa]

So Ray, is that you beating your head against the wall over on the Tivo forum about this? Thanks to that news piece, the same type of arguments are flaring up over there. The saddest part is that the loudest defender of the elevator isn't doing so out of any first hand knowledge, but because the article told him that there are PhDs and stuff working on it, and that NASA helped pay for it, so it HAS to be right.

People who guard their ignorance more viligantly than their wallets are indeed morons, and Ray has every right to express his exasperation in having to deal with them.

Eric,

Nothing I wrote was intended to insult or denigrate any new idea. I simply applied my knowledge to the claims and found problems that I think should be addressed. If those are properly addressed I'll revise my position. Until then I'll maintain that the concept won't work. I do so not to stifle new ideas, but to ensure that new ideas have merit and can stand up to scrutiny.

Andy

 

[Yee-Ming]

My head hurts... :frowning:

Unsurprising for a fellow who barely passed physics in high school. Then again, I was concentrating on my other 3 A level subjects (which is all I needed for university admission).

But at barest minimum I know that any potential space elevator needs to be based on the equator. Clarke's book postulated one at Sri Lanka, which is (coincidentally) where he lives. Fountains of Paradise, I believe, although as usual I could be completely wrong.

 

[Max Leung]

I think we should send Ben Affleck into space as a test pilot for one of those new-fangled private-enterprise space plane tests. Maybe take J.Lo and they can both be the first couple in the 10-mile-high club!

Then we can justify the media attention on him and J.Lo!

And yeah, a space elevator is impossible with current tech. Unless someone invented a material that is completely and utterly indestructibe?

Or maybe we can carve up a neutron star, and use the bits to make the links of the elevator! Yeah! I just hope the mass of the elevator doesn't knock the moon out of orbit!

 

[Jack Briggs]

Yee, you are correct about the Arthur Clarke novel (which also happens to have been his last Hugo Award-winning novel).

 

[Mark Schermerhorn]

ooooo space elevators I was fascinated by the idea when I read the Mars series of books by Kim Stanley Robinson.

Andrew Testa: I was thinking about the angular momentum problem. Say you have a stationary mass X sitting at 1.5 times the distance of geostationary orbit on the teather, a cart of mass X/2 on the ground, and another cart of mass X/2 at geostationary orbit. If the carts were to traverse up and down the teather at the same time at the same velocity, passing each other at 0.5 times geostationary orbit, the center of mass should be conserved, right?

Granted this means your net payload is 0 Kg since your carts have to be the same weight at all times. However, if we're out mining the asteroid belt we'd be sending materials back anyway. Even if we just sent back a bunch of junk moon rocks there should still be a net energy benefit, since the energy to escape the moon's gravity is much lower than earth's.

Beyond that, I think the only hope to the fuel problem would be a propulsion system that runs on sunlight, like solar sails.

I think for fun I'll go back and see if KSR spoke to this issue as well as the wobble problems you talk about. I vaguely recall them being able to wind up/let out the teather along with "compensation boosters" to deal with wobble but that might be my imagination. This stuff is so fun to think about

 

[Andrew Testa]

Damn! Lost another long post to an inadvertent page closure.

Mark, your example is a good one, and illustrates nicely some of the problems of orbital physics. While you can conserve the CM position, you cannot also conserve the angular momentum. This is because the CM is determined by the distance from the Earth center, while the angular momentum is determined by the square of the distance. So they cannot both be conserved at the same time. In your example, the angular moment (L) is almost halved when the carts pass in the middle, so they accelerate to twice the orbital velocity to compensate. This pulls the first half of the ribbon out of alignment and pulls down the CG. If you try to conserve L, then the point the carts have to pass is appromiately 28,000 miles, or almost at GEO. The CM here is raised, so the CM accelerates to try and move into a higher orbit. It can't, so it accelrates to a higher angular velocity.

So you see, you can't conserve them both at the same time. Both situations require either the CM or the payload carts to have chemical rockets applying forces to the system to maintain the status quo. Once again, you wind up having to expend a lot of fuel accelerating various portions of the elevator or payload to maintain the integrity of the system.

Cool thought experiment, eh?

Andy

 

[DaveGTP]

are PhDs and stuff working on it, and that NASA helped pay for it, so it HAS to be right.

I haven't joined the thread here, just reading, but I have recently read 2 different stories in my engineering ethics class: One about NASA doing SDI (the so-called 'star wars defense' that never could even potentially work) and one about the Challenger explosion (the launch was fought by quite a few of the primary engineers/scientists, but went forward anyway). In both instances, NASA had a bureacracy problem - the willingness to do thing for political and public opinion reasons rather than the actual recommendations of scientists. I'm sure a little googling will help you find the information. One of them might be a good arguing point for you.