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Effect of Edward's space elevator on private space travels?

Posted by: Ekkehard Augustin - Tue Jun 29, 2004 7:20 am
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Effect of Edward's space elevator on private space travels? 
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Post    Posted on: Fri Jul 02, 2004 1:44 am
you do realise that when you are orbiting, you are already falling, but just constantly missing the earth? To fall AND hit the earth you have to have reverse thrust (or atmospheric drag in a REALLY low orbit) enough to get your velocity low enough to hit the earth.


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Post    Posted on: Fri Jul 02, 2004 8:04 am
Autochton wrote:
we could easily assume that a lifter could be built to take cargo to this altitude. So if we have a tether that starts at just over 100 km altitude, and then has an orbital center much further out, giving it a relatively low orbital velocity (perhaps in the few hundreds of km/h, projected to Earth's surface)

Don't fall of your chair, but I agree with you here. Assuming that we have the technology to build a tether (completely different argument), then a combination of lower atmosphere lifter with the set up you describe might be reasonably practicable. But instead of a derivative of Rutan's SS1, why not use those big bloody floating platforms (apparently they have a potential for heavy lift) that are being designed and tested by JP Aerospace.

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Post    Posted on: Fri Jul 02, 2004 8:25 am
The technology needed for the tether seems to evolve. Within the last four years I've found and read several articles considering nano-carbontubes.

Some of them agree to Edwards and the others are considering aspects irrelevant in this discussion.

In his documents Edwards says that the technology will be available within 15 years - the articles I read are reporting results that are progreses towards the tether.

To consider the role of private spacecrafts - the nanotubes will have to be tested. And the best way would be test in that environment being their destination - in space. Private spacecrafts are the cheapest way to get a little probe of the nanocarbon-tether to space. There it could be shot with screws and other possible debris the tether of the elevator has to survive later.

Perhaps other pieces of nanocarbon-tether can server as shields against small debris.

And in the nano-carbontubes can flow water and other fluidables - may be they can be used for cooling purposes? At reentry? If that is so that can reduce the price of the tether.



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Post    Posted on: Fri Jul 02, 2004 2:02 pm
noone seems to understand my question, if you go up on a space elevator you are not going at orbital velocities, I know when in orbit you are "falling but always missing the earth" I am asking if someone could go up on a space elevator and get into orbit with a minimum of thrust using the earths gravity to accelerate?


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Post    Posted on: Fri Jul 02, 2004 2:48 pm
If your space elevator takes you from an (immobile) station on the ground, to a point 22,282 miles (or something like that) straight up (at whatever rate of ascent you like, it doesn't matter) ... you are now in orbit (going around the world at a rate of 1 revolution (?) per day, i.e. geosynchronously).

Just step off the platform and there you are ...

(later) ok, wait wait ... if you place some sort of counterweight slightly higher than the 22,282 mile platform, then this counterweight (being held geosynchronously) would tend to want to go "up" due to centrip-, centrifug-, something forces (is there a physicist here?) ... so attach a second tether to the counter weight and also all the way down to your elevator platform, let the counterweight fly up ... pulling the platform along with it ... would that work?

Whatever, but that still aint using gravity.

Hmmm you posed a prickly one boyo.

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Post    Posted on: Fri Jul 02, 2004 4:27 pm
I mean't if you were in a lower orbit, what is the lowest you could go on a space elevator and still get into orbit with a minimum of thrust?

Are there any aerospace people here? Or just interested amatures?


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Post    Posted on: Fri Jul 02, 2004 10:47 pm
Texan I am having a hard time understanding your question. You you mean what is the velocity you would need to obtain LEO if you just stepped off the elevator at, say, 300km up?


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Post    Posted on: Fri Jul 02, 2004 11:28 pm
I was thinking higher, but yeah something like that....


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Post    Posted on: Sat Jul 03, 2004 12:17 am
Dr_Keith_H wrote:
(later) ok, wait wait ... if you place some sort of counterweight slightly higher than the 22,282 mile platform, then this counterweight (being held geosynchronously) would tend to want to go "up" due to centrip-, centrifug-, something forces (is there a physicist here?) ... so attach a second tether to the counter weight and also all the way down to your elevator platform, let the counterweight fly up ... pulling the platform along with it ... would that work?
I think it might have some prickly problems about orbital velocity. When you increase the radius of the movement, the angular velocity will decrease unless energy is added. For an example, sit and spin on an office chair with your arms close to you, then stretch them out from your body. You'll go slower. The opposite case is also true. (A small example for those readers unfamiliar with centrifugal force.) By 'dropping' the counterweight outward, you move the elevator's mass center outwards as well, and that causes its orbit to change. You dcould send the whole thing whiplashing around the Earth that way... Ow my planet. :)

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Post    Posted on: Sat Jul 03, 2004 5:35 am
TExan,

Orbital Velocity- Your relative velocity at whatever altitude you are at= what you need to stay up at wherever you are at. You're going to fall fast, so it has to be something quick. Ion engines and electrodynamic tethers wont cut it. Has to be a rocket, but also can't damage the ribbon.


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Post    Posted on: Sat Jul 03, 2004 2:14 pm
A 'Hellevator' would be very ill suited to getting to LEO, but a godsend for further out. To get to LEO, you need to increase your speed from the velocity of the elevator tether, so you'd have to step off the elevator, and accelerate fdiercely from there. Of course, you could attain LEO by stepping off it above your desired altitude and accelerating to orbital speed during the first portion of your fall - but you still need to make your velocity vector be parallel to the Earth's surface for an orbit to work, and long enough that gravity won't point it downward for you faster than you can move to keep it above the horizon.

Am I making sense? Thought not. :) An orbiting object has a velocity vector that at any given point in time is parallel to (or very close to) the Earth's surface at the point directly below (assuming a perfectly spherical Eatrth here...). This vector also needs to be long enough that it is not pulled so far out of whack by gravity that it ends up pointing downwards. Basically, a good orbit's velocity vector has a size so that when the object has moved for a duration (and been subjected to gravity for this period), its velocity vector is still parallel to Earth's surface. The lower you go, the stronger Gravity pulls. Therefore, the higher your velocity needs to be to cancel it out.

A space elevator will be moving at either a very low or no speed at all in relation to the Earth's rotation speed, and this speed is quite a bit lower than what you would need to cancel out gravity at a low altitude. However, for up near GSO, it's just right. So stepping off a space elevator would have to grab a load of velocity to stay aloft, or they would plummet like a rock toward the planet, pulled by its gravity.

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Post    Posted on: Sun Jul 04, 2004 8:10 am
Quote:
For an example, sit and spin on an office chair with your arms close to you, then stretch them out from your body. You'll go slower. The opposite case is also true. (A small example for those readers unfamiliar with centrifugal force.)


As consequence, when the space elevator goes up, the earth's rotation will slow, and when it comes down, the earth will rotate faster. Probably not enough to make any percievable difference unless we start lifting significant mass with the elevator. I wonder if the weather patterns would be affected, though?

The space elevator tether would be mounted at a point on the equator, and the exit platform could be at the exact height to maintain geostationary orbit (35,700km above the earth's surface.) There, the orbital velocity mismatch at the exit platform would be nil. The counterweight would need to be higher, as previously mentioned such that the center of gravity for the ribbon + counterweight was at the exit platform location.

Interesting safety implications. The counterweight would move at a faster speed than other orbital objects at its height. Collisions would be more likely. After a collision, the ribbon would become slack, and if the counterweight falls out of orbit a pretty nasty situation could develop. Think about all the kinetic energy the ribbon would have, and the potential for it to slice object if it was out of control.


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Post    Posted on: Sun Jul 04, 2004 6:31 pm
Hello, Texan,

if an object is released by the elevator at an altitude BELOW the geostationary altitude of 36,000 Km it has to be accelareted to keep it at that orbit and to prevent it from falling to the surface.

If another object is released by the elevator at an altitude ABOVE the geostationary altitude it has to be decelerated to keep it hat orbit and to prevent it from disappearing into the interplanetary space.

When not released the object is secure beause the elevator is holding it and the elevator itself and its tether ist prevented from falling to the surface because it is locked at the counterweight in the geostationary orbit. This way its prevented from disappearing too if the elavator holds above geostationary altitude.

Climbing along the tether to he altitude wanted no special thrust is needed because the elevator is mechanical locked to the tether. Please have look into Bradley C. edwards' documents at the NIAC site - the final report includes good graphics and pictures showing how the elevator will climb.



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Post    Posted on: Mon Jul 05, 2004 12:19 pm
If I'm thinking this through correctly, building a station into the counterweight and anybody in that station will experience a gravity like effect. The amount depends on how far out the counterweight is. The centre of gravity point that is in perfect orbit can be where space craft dock and launch from. The small station is where station personel can live, all the time commuting up and down to the zero G launch station.

Is this right? I think so.

And the mention of a magnetic lifting of the elevator could work. If we've got to the point where we can manufacture enough nanotubes to make an elevator cable, then there will be enough to beef things up. I thinking that we can borrow ideas from the textile industry. Sew into the cable all the facilities you need. Piping and conduites can be manufactured into the tether. As long as the tensile strength of the tether is enough to hold it's own weight and that of anything we lift. And that can be achieved by adding more nanotube strings.

Which also brings up another idea I've had. If there are pipes inside the tether, then fluids can be pumped to and from the counterweight to keep the centre of gravity where it needs to be.

Mmmm. I'm gonna pose something else too. Sorry. Here in the UK, we have a tourist spot where a cliff train travels up and down a very steep cliff using no power at all. Well, it is powered, but it's powered by water from a river that used to fall over the cliff edge. The water pours into buckets on another track, attached to cables and pulleys that lift the trains from the bottom of the cliff. You can probably see where I'm going with this. If you have two tethers, one as the guide, and the other as the lifter, you could alter the centre of gravity of the lifter such that the payload is lifted off the earths surface.

Anyway, there I think is more than my tuppence worth.

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