Space Elevator

[unclesyd]

The race is on.

 

[GregLocock]

Got a link?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[unclesyd]

Here is the links to a lot of information. It has been on the news in bits and pieces for a couple of days.

http://news.google.com/news?sourcei...005-40,GGLG:en&q="Space Elevator"&sa=N&tab=wn

 

[maleck]

link is dead

 

[maleck]

hi folks, I have 3 very nice new links !

http://www.zadar.net/space-elevator/

http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html

http://science.nasa.gov/headlines/y2000/ast07sep_1.htm

Cheers,
Maleck

 

[swearingen]

One mile up is way short of where aircraft fly, let alone 1/4 of the way to the moon. I've followed this for years and done my own share of calculations (remarkably similar to those on zadar.net). The more I look into it, the more skeptical I become. I say that it may be possible, given serious advances in material science, but not feasible in the same vein that it is possible to put Lake Pontchartrain on Charon, just not feasible for many reasons.

 

[maleck]

Hi swearingen, thanks for sharing your opinion. You have mentioned "I say that it may be possible, given serious advances in material science". What are those for example ?

Have a nice weekend,
Maleck

 

[swearingen]

Maleck,

What I meant by my statement is that the "super-cable" just isn't here yet on a scale that would be necessary. As stated on the zadar.net page, the use of this cable is very dependent on the density/tensile stress ratio and the one required is a pretty impressive material.

There are many other problems with the theory that I haven't seen properly addressed. The zadar.net page talks about transverse wave speed briefly, but what of them? Their causes and effects? What about longitudinal waves? The harmonics questions are the biggest problems in my mind. The questions of energy balance and how much fuel it takes to accelerate you to the tangential speeds required while still hoisting a useable payload still have not been answered satisfactorily. The cable will lag because of atmospheric drag and this lag will vary greatly which continuously changes the orbit of the weight at the end - what of those effects? Not to mention all of the above affecting your coriolis forces. Now, on to construction: how do you catch that cable hanging down from space and pin it to the earth? The cable is lagging, due to the atmosphere, in the opposite direction to which it will lag when connected and stabilized - how is that dealt with? This lag will produce a whip effect that will send waves up the cable and wreak havoc on the guys at the other end, especially as the cable's diameter gets smaller as the wave passes geosynchronous orbit. The wave velocity may not change, but the amplitude sure does. Think of the last car of a roller coaster or the last person in a chain of ice-skaters. Coriolis issues under construction are a big deal too - how do you continuously increase the angular momemtum around its own centroid as its moment of inertia grows while being constructed? Granted, you've got some tidal force helping you, but that force is not constant along the cable length which would produce - you guessed it - waves in the cable.

All of these issues plus MANY more must be thought through and solved before this project ever gets out of the design stage. I won't hem myself in and say that it's impossible, but I will say that it is very highly improbable...

 

[maleck]

Great post swearingen ! You've raised many crucial points !

 

[swearingen]

I had assumed that my post would have spurred lots of debate. I guess I was mistaken. Surely I haven't put this to rest?

 

[maleck]

This post was not originally created by me, however ...

... I guess they are not making any comments because the subject is so complex that they just did not fully understand or because they are occupied, swotting to make all the necessary calculations you did

 

[Kenneth]

http://www.seattlesampe.org/newsletter/3-2006 flyer.pdf

 

[Boothby171]

Stupid Question:

Assume (for the moment) that you have no drag or wind or standing or travelling waves on your cable. It's just a straight cable, running from the surface of the earth out to a geostationary satellite.

Where the cable starts, on the surface of the earth, is also a geostationary point. Yet at that point, whatever delta-length of cable you've got there weighs in at Wgt = delta-mass * 100%G. As you move up this perfect cable, the weight of that section reduces, bit by bit, to Wgt = delta-mass * 0%G.

Sum the force vectors. You don't have a force pulling the cable up (as I keep seing people implying by talking about cables that thin out as they go up, or by talking about huge anchoring stations on the surface and sub-surface of the earth); you have a "net" force pulling the cable down. The cable has to be thicker on the top. The "satellite" has a lot of extra weight to support (and just how does that work?)

Every once in a while, I really like it when people smarter than me prove me totally wrong. This is one of those times.

--Steve

 

[GregLocock]

there is a counterbalancing cable running outboard of the satellite, since it is rotating at the same angular velocity it exerts a net outwards force, thereby compensating for the weight of the inboard cable.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Boothby171]

Has anyone ever done an ADAMS or other physics simulator simulation of all this, all the secondary (etc.) effects, loss of cable responses, etc? Or are we all discussing how many angels can dance on the head of a pin?