Slashdot Mirror
Space Elevator Challenge
MattSparkes writes "For the second year in a row, no team has won the $200,000 prize in the Space Elevator Challenge at the Wirefly X Prize Cup. Three teams were disqualified before the contest even started. Another competition at the event has been held up by confusion. Incredibly, it seems the organisers of the competition are not sure whether the ribbon used was 50 or 60 metres long, and whether any team completed the climb fast enough to win."
The competition was for building a vehicle to climb the ribbon, not making the ribbon itself.
There is a seperate competition for designing/making the actual ribbon.
Ref: http://www.elevator2010.org/site/competition.html
=Smidge=
If you attach a weight to a rope and spin it around your head the inertia of the weight will keep the rope tight. Because the Earth rotates, a large mass a long way out in space should be able to keep a line tight. The bottom end would be attached to the Earth, preferabley close to the equator. A station close to Geosynchronous orbit will be in microgravity. The weight at the end of the cable will experience rotational pseudo gravity. Objects dropped from this point will enter solar orbit.
http://michaelsmith.id.au
Can anyone enlighten me how that thing supposed to work?
See Wikipedia.
We fasten one end on ground and second end is fastened... where???
To an orbiting counterweight.
And what about Earth rotation?
Earth's rotation is what makes it work. Otherwise:
I still think that normal elevator - a-la tower - is much saner idea and can be achieved easier
Yeah, nobody ever thought of that idea. They're pursuing orbital tethers because they're all insane masochists.
A tower would be much more massive and would have to support its full weight. Tethering to an orbiting counterweight allows centrifugal effects to lighten the total load, since the Earth is rotating. You couldn't build one high enough to reach geosynchronous orbit, and thus whatever you brought to the top wouldn't be in a nice circular orbit when it got there; it would still need something like rocket thrust. With a tether, as soon as you get up to geosynchronous, you're automatically in a circular orbit. See the "compressive structure" entry on Wikipedia.
Tower doesn't have to be all that tall. It must be high enough to fraction Earth gravity force by e.g. ten - requiring ten times less of fuel to launch elevated rocket.
Reducing the force of Earth's gravity by 10 doesn't equate to 10x less fuel. The fuel required is a function of the change in velocity needed; it's more related to reducing energy than reducing force (1/r vs. 1/r^2). See the rocket equation.
Anyway, the altitude required to reduce the force of Earth's gravity by 10 would be almost 14,000 km above the Earth. And you still wouldn't have the right velocity for orbital insertion.
With "space elevator" - no such gradual progress seems to be possible.
Orbital tethers don't have to be geosynchronous. See tether propulsion. Besides, if you crunch the numbers, you will find that a compression tower has to be quite high before any substantial benefit in fuel reduction is achieved.
The cable will probably not oscillate at all (almost) because the cars will ascend at approximatively 100 km/h, by far too slow to do anything except a very small (less than 1 degree) lean at the very bottom of the cable (remember that a lot of payloads will probably be release before reaching 10% of the total cable length).
More details on Wikipedia and googling for "Annual Space Elevator Conference" (there are several simulation for the dynamic behavior of this thing).
There's a hidden treasure in Python 3.x: __prepare__()
If you can make tether that strong and light, you can use N of them to make tower stand. Materials for such tower also can be very very light and very very hard. But probably to not such greater extent tether has to be strong.
What makes super-super-strong tether in your mind possible and super-hard and super-light tower impossible?
Well, for one thing, tensile strength and compressive strength aren't the same thing. A substance which would withstand the pulling force of a fixed space elevator (from earth's surface through GSO to a counterweight) would not necessarily be able to withstand the compressive force of supporting its own weight.
Then there's the balance issue. If you build a tether with its center of mass at GSO, it's in free orbit around the planet. This means it has zero chance of falling over, whereas a shorter tower's center of mass would need to always be over its surface footprint. The higher you make the tower, obviously, the harder this is to maintain.
If you can make tether that strong and light, you can use N of them to make tower stand. Materials for such tower also can be very very light and very very hard. But probably to not such greater extent tether has to be strong.
This is simply untrue. If I'm standing on top of a building and lower a rope to the ground, someone can climb it. This doesn't mean you can build a tower of that height out of the same material (a rope). (In this analogy, the top of the building is the counterweight on the end of the tether, which holds it taut)
But how heavy it would have to have? I shiver to even think that thing might alter (or even de-orbit) Earth. The wikipedia page doesn't answer that question.
It doesn't answer this question for the same reason it doesn't answer the question of whether the Klingons will think that the tether is a threat to them, and therefore attack the human race: it's a complete non-issue. For one thing, the earth gets heavier every day, as crap from space falls into it (from dust all the way up to visible meteors), probably more in a year than the mass of the asteroid counterweight. I'm not worried about de-orbiting the planet anytime soon, are you?
If you're really worried about it, let's make the counterweight out of material taken from the planet, thereby not changing the planet's mass at all, and therefore not affecting its orbit around the sun.
I don't think you grasp how much mass and velocity the planet has.
Reality has a conservative bias: it conserves mass, energy, momentum...