space elevator

davej

This has idea has been knocking around for years but it seems that nasa are at least giving it some consideration:

http://www.isr.us/spaceelevatorconference/aboutSE.html

davej

Sarky

It's about time. If they pull the finger out and really go at this, space travel might even be a viable option in 50 years or so.


For the US, at least. I can't see them sharing this for the good of humanity, assuming they manage to get round to building one.

MarVeL

Was reading about this on wired earlier today. One of the big problems is appraently all the junk thats up there and how the "cable" would handle the impacts. Nice to know that we've already polluted space (at least around our planet) enough to cause us problems isn't it?

Capt'n Midnight

Very old idea - very easy to do on the moon

But what are the fibres made of ?

(easy enough to get rid of the junk - just lift ICE into orbit - will quickly vaporise - but should take out the kenetic energy of objects first...

Think A. C. Clarke had a book about that - he had the tower in SriLanka.

Using a captured asteroid as the in orbit ancher point would be tricky but nice..


The other idea for the moon was a spinning asteriod with cables reaching down to the surface - as something arrived to land there it's momentum was added the asteroid and so a similar amount of momentum was available to whip something into orbit..

davej

I guess one major obstacle to this (especially in the current political climate) is the threat of "terrorism". I can imagine that the maintenance, safety and security checks for the system would be a bit of a logistical nightmare.

Another advantage of the elevator would be the fact that the top of it would be moving at a relatively high velocity (faster than the escape velocity). So you could launch stuff from it for "free".

But when you think about it, it isn't really any more crazy an idea then igniting a controlled explosion under your ass.

davej

mike65

Originally posted by Capt'n Midnight


Think A. C. Clarke had a book about that - he had the tower in SriLanka.

I have an article Clarke wrote in 1979 about this notion. It was published in Future magazine which mixed science fact with fiction.
I think I have it in the attict somewhere!

Mike.

Capt'n Midnight

Eh - no it would not be escape velocity.

Orbital velocity is the min needed to orbit the earth (88minutes)
so 24,000 miles in 90 minutes = 18,000mph

Escape velocity is when you no longer orbit the earth - can't remember offhand if it is twice or root(2) (1.4142) times the minimum orbital velocity

The tower would get you to geostationery orbit - ie once around the earth in 24 hours - if you stepped off below the 36,000 Km mark (need more accutate figure) you would fall back down to earth because you did not have the velocity to orbit there,


NOTE: someof the tower must be above the geosynch orbit to counter balance the effect of gravity on the bottom of the tower.
Anything stepping of the very top would drift out further - some calculation would give the delta-Vee needed to do this (or how high the tower could extend)

also have a look at (sp) Legrange points - there are 5 areas in a two body system where a small body will stay in place. They also make interesting points to aim for (a tower could give enough umph to get to one of these points - not all - because some are much lower in the gravity wells than others)

Syth

Very old idea - very easy to do on the moon

I can't really see the point of doing it on the moon, there's no athmosphere, and a weaker gravity, so ther arn't the same factors. Not to mention that there is more people on earth.

'Red Mars' by Kim Stanly Robinson deals with the first martian conoly, and they did a similar thing on Mars. The martian freedom fighter knocked it over and it wrapped around the planet one and a half times. Imagine if that happened here...

Capt'n Midnight

It would take quite a shove to bring it down - the delta Vee would be in ~3,000 mph at least - and if the unhooked the cable at the bottom they could reel it in and just settle in a lower orbit (12-15hrs rather than 24hr)

It would be much easier to build on the moon
even with it's low gravity a single stage rocket must be 50% fuel to get to orbit (or if you land and then take off then only 25% of the total mass will get back in orbit again) - still way better than 90% fuel on a two stage earth flight.

mass drivers would make it very easy to build on the moon

You would then move it to earth orbit and drop the cables down..

You see this project is to big to build from the earth and since the moons gravity is a sixth of that here and the cable run is shorter the costs of build a moon evlevator are negligable if you are building one here.

Also have a look at high pressure water as a structural material,

Sarky

Designing something that tall so that it would actually stay up would be the only real difficulty(albeit a pretty big difficulty...).

Once erected, the rest would be relatively easy. Even building a second elevator would be greatly simplified due to the existance of the first.

Capt'n Midnight

You can't make something that tall - think of it as a rope anchored at the top - the whole thing is in tension.

Building up would only get you a few miles - you need a few thousand. - Ok identical masses weigh less as you get higher but that don't help much.

You'd have to reel it out slowly since the kenetic energy at the bottom would increase massively as it got closer to the surface...

Lets say it was made of a cable one cm 2 in area
you would need 3,600 m3 of it. (it was made of steel then that's 10,000 tons) - so the cable needs to be much thicker at the top just to hold it's own weight. (which means it's a lot more than 10,000 tons to hold up so it gets heavier and thicker again)

GuanYin

I think the concept is a two way pully system. But its not a solid structure. What you need is a satillite at about 22,000 miles which will maintain a synchronous orbit

It would most likely need to be built from the top and lowered down and for this the initial energy and cost would be huge.
However once built the elevator, mining of astroids, maybe the moon and othe rdebris collected could be sent back to earth, generating the energy to pull equipment, machinery back up, so in the end, the elevator would probably run itself energy wise.

Capt'n Midnight

[quotes]
S. I can't really see the point of doing it on the moon, there's no athmosphere, and a weaker gravity, so ther arn't the same factors. Not to mention that there is more people on earth

S. It would most likely need to be built from the top and lowered down and for this the initial energy and cost would be huge.
[/ quotes]

Seeing as how even a single 1cm cable would weigh thousands of tonnes - it would be better to source the raw materials on the moon - and it would provide valuable experiance and proof of concept ...

GuanYin

I think the biggest problem with this is the material for the cable.

The tower itself would only need to be about 10 miles high, or less if mountain based, but for safeties sake you might want that tower to be out at sea.

The cable is another matter, tension of the cable increases with altitude so you would, as has been pointed out need a material with enough tensile strength to cope up top, without being miles across. I've seen the predicted tensile strength required quoted at 63 gigapascals which is roughly 15-20 times more than our current best bet material (Kevlar).

The initial concept was actually devised in russia in 1960, it was adapted by clarke in 1963 as a way of increasing the amount of satillites the earth could manage, but he didn't actually use the "space elevator" idea until 1979 in his book The Fountains of Paradise.

Cuauhtemoc

I've seen the predicted tensile strength required quoted at 63 gigapascals which is roughly 15-20 times more than our current best bet material (Kevlar).

Supposedly they're developing strong enough material in the form of Carbon nanotubes which have a tensile strength of 200 gigapascals.
Don't know if it's in production or not though.

GuanYin

I'm willing to be corrected on this (and god knows I'm sure karma is just waiting) but the carbon nanotubes we can produce have a tensile strength of about 150 gigapascals.

I didn't mention them though because at present we can only make them at a thickness of about 10E-6 metres thick. If we could bulk that up to about 10E-2 metres or so we would be in business.

Capt'n Midnight

http://www.vectorsite.net/tarokt4.html
LOTS of other ways to get to orbit
- "rotating skyhook", "rotavator", or "bolo", & SPACE FOUNTAINS

Note: if you make an elevator over the ocean it could of course be moved to another site - though not very fast .

http://www.physicspost.com/articles.php?articleId=141&page=2
“The space elevator will be built about 50 years after everyone stops laughing.”

http://www.space.com/businesstechnology/technology/elevator_update_020819.html

Twenty tons of cable and reel would be kicked up to geosynchronous altitude by an upper stage motor....
Once secure, a platform-based free-electron laser system is used to beam energy to photocell-laden "climbers". These are automated devices that ride the initial ribbon skyward. Each climber adds more and more ribbon to the first, thereby increasing the cable's overall strength. Some two-and-a-half years later, and using nearly 300 climbers, a first space elevator capable of supporting over 20-tons (20,000-kilograms) is ready for service...
"If budget estimates are correct, we could do it for under $10 billion.

http://www.space.com/businesstechnology/technology/space_elevator_001226.html

Space tethers - can catch and eliminate space junk?
http://www.sciencevictoria.org.au/ord0700.htm

Capt'n Midnight

http://www-istp.gsfc.nasa.gov/Education/wcurrent.html

Faraday nevertheless speculated that the aurora (which he believed to be an electric phenomenon) might be powered in a similar way by the Gulf Stream flowing to the north-east through the Atlantic Ocean, beginning just offshore from the US.
Of course, what Faraday forgot here was that to connect the ocean to the aurora, the current would have to cross the lower atmosphere, which is an excellent insulator and would block its flow

Carbon nanotubes conduct electricty - so in addition to that generated by by it's length - would the short circuiting of the atmospheric insulation affect the aurora or worse affect the shielding from cosmic radiation ???