Space elevator: is this the start of cheap space tourism?

[luke pitt]

As you may well know at the moment space tourism is very (VERY) expensive; but that may change.

I have heard about plans for a "space elevator" which is essentially a big cable that gets held in space by centrifugal forces. On this things just climb up into space, removing the whole expensive part about actually fireing a rocket into space.

Of course is is all still in the initial stages of development so it will be many years until it is actually around. and probably a bit longer for it to start taking tourists

if you want to know more about it try here

still, somthing to look out for in the future

[gonenorth]

This is yet another nostrum from science fiction, and one I've never understood. ( I believe Asimov, Arthur C Clark and Kim Stanley Robinson have all featured such a device in their stories).

If you could get it to work, it would be fabulous. However, I'm struggling with the following: the cable passes through the atmosphere - drag/friction (to say nothing of meteorological conditions) would surely have a tendancy to act as a 'brake' on the cable, pulling the orbital station downwards (and backwards ???). To compensate, the orbital station would have to be under almost continual powered thrust, which would be incredibly expensive. (It seems to me the 'elevator' would be working full time just to ship the necessary fuel up to the O.S.)

I'm also puzzled about wether the cable would take the strain. As I understand it, geostationary orbit is normaly around 22,000 miles above the surface. If the cable weighs 4kg/meter (see here) then this is a total mass of around 160,000Kg: way over the breaking strain ! So we are presumably talking of some exotic alloy.
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[bdunbar]

I have to say that space elevators will for some time not be for passengers. The first ribbon will be for cargo only.

The carrying capacity will be - for people, given the length of the trip, iffy. Our first lifter will be able to lift a max of 20 tons, gross. That includes itsself of course - call it 13 tons for cargo. If you carry people past LEO you'll be spending several hours in the Van Allen belts, exposed to some fearsome radiation - to sheild against that will require more weight than we can carry.

The atmosphere does act on the ribbon, but not (we think) in such a way that will cause drag, or not so much drag that cannot be overcome by the counterweight. Only a small percentage of the ribbon will be in the atmosphere.

The ribbon material is (must be) made out of a CNT composite woven into a braid. There simply is no other material that can be made light and strong enough. And we've no little problem there - the CNT material exists in the lab, but not available commercially.

~brian
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Brian Dunbar
Liftport

[PeterW]

What is CNT?
I guess the studies on drag and stuff must have been done, but it still seems like a lot could go wrong. What would happen if the cable is sheared by some space junk? This is still accumulating and severa time a Shuttle has had to manouver out of the way.

Would you then expect to have some kind of manned sation at the space end and take the people up by conventional means?
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[Trev]

I'm a bit confused even after reading the sites.

What's at the other end of this ribbon? Presumably there's got to be something it's attached to at the space end or is it just a ridged solid rope?

Where is the ribbon going to end up? Is it for example to take things to the International Space Station or as seemed to be suggested somewhere, Mars?


Trev
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[bdunbar]

"What is CNT? "

(AKA. Bucky™ tubes), a member of the fullerene family. Individual single wall nanotubes have the electrical conductivity of copper or silicon, the thermal conductivity of diamond, and also happen to be the stiffest and strongest fibers known. Their molecular perfection enables them to be manipulated using the versatile chemistry of carbon. [Carbon Nanotechnologies, Inc., US] http://carbonnanotech.com/CNI_home.html
www.bioon.com/book/biology/genomicglossaries/miniaturization_glossary.asp.htm

The idea is that CNT form the basis for an ultra-liight, ultra strong material that can be used in for a variety of purposes - as structural members, vehicle bodies, armor and cables.

"What would happen if the cable is sheared by some space junk? This is still accumulating and severa time a Shuttle has had to manouver out of the way. "

Depends on the size/velocity of the junk and how the ribbon is designed. There are altitudes where there is more junk - the ribbon can be shaped to minimize damage from a puncture. But yes, if something large smacks into the ribbon there will be damage. What happens after that depends on where the impact is. Below the break the ribbon will fall, and break apart due to friction and heat. Above the break the ribbon ascends into orbit.

"Would you then expect to have some kind of manned sation at the space end and take the people up by conventional means?"

Someday. It's unlikely that we'll hang things ON the ribbon but at GEO anything parked next to the ribbon will tend to stay there (with good station keeping) so .. it would be a good place to locate space hotels, stations etc.

People however are problematic. They want air and a reasonable environment. Shielding to protect from the Van Allen belts (very intense radiation areas) will be needed - Apollo went THROUGH the belts quickly but a lifter is not moving that fast. It's possible that in time people will use an elevator, sure. But not the first SE - too many reasons why a 'people SE' would be a deal breaker.

"What's at the other end of this ribbon? Presumably there's got to be something it's attached to at the space end or is it just a ridged solid rope? "

Well nothing is at the other end but itself. Early SE ideas had a smallish asteroid at the other end for a counterweight but this puts the SE into the improbably column - we have problems getting Shuttle to orbit, let alone a missio to capture and bring back an asteroid. The idea is that you get the equivlent weight by simply extending the ribbon.

This is simplistic (very much so) but take six foot lenght of rope. Grab one end. Twirl in a circle. If the far end as a rock you don't need to twirl fast - the rock pulls it out. BUT. Extend your imaginary rope out by twenty feet or so, no rock. The length of the rope gives you some additional weight, the momentum imparted by the rope itself give you the rest.

Now - the rope analogy is strained, I admit. An SE is dangling down from orbit, and dangling up FROM the midpoint to the far end.

"Where is the ribbon going to end up? Is it for example to take things to the International Space Station or as seemed to be suggested somewhere, Mars? "

ISS is, actually, in the wrong inclination and altitude to be at the midpoint for an SE. Mars is a viable place to park an SE.

Mars is, in my opinion, not going to happen for an SE. There are no current manned missions planned FOR Mars. Drones and robots do pretty welll getting there by the current "fly there and drop them into the atmosphere" method. Any manned missions I've seen planned don't have enough scale to make an SE cost effective. The same objections apply to the moon.

Liftport anticipates that people will use an SE for exactly the same things we currently use rockets for. Resupply missions to ISS and whatever space stations follow. Lofting satellites. Missions to the moon - exploring drones/robots and supply missions for whatever manned missions go there.

The thing we have going for us is that an SE can scale to accomodate traffic at an average throughput of 20 tons gross per day per ribbon. Which should let us bring the price down below $500 per lb which will let us increase the traffic (more ribbons) which brings the price down more .. a virtous circle.

We've some documents and FAQs on this at www.liftport.com - but I enourage you to look up the facts for yourselves and make up your own mind.
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Brian Dunbar
Liftport

[ooen]

Here's a website about space elevator. You may need to register, but it only takes a minute or two. Good webcast.
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[lightningbob]

The biggest problem with the "Space Elevator" is it probably won't work.

1. It must be longer than Geo synchronous orbit 22,000 MILES!!! (give me a break sheesh) and have a counter balance past that point.

2. It would have to be assembeled in space and lowered to the surface. .......that's alot of material to ship to geo-sync orbit. The cost could never be justified.

3. Scientists have concluded that just 1 (one) carbon molocule out of a million that wasn't alligned properly could weaken the structural integrity and cause it to break. (At a length of 22,000 the possibility of failure is very high)

4. When carbon nanotubes can be constructed to usable lenghts they wiill be better used as space ship components (Hulls, tanks, toilet seats ....ect)

Yes the idea of "Walking" into space is fantastic but I really think were going to have to go another way. But don't worry. We'll get there.

[DrEmilioLizardo]

I'm not sure why people are even considering space elevators.