Highlift Systems' Space Elevator In The News Again

Kris_J writes "Highlift Systems may have found a second location for the anchor of their space elevator -- Perth, Western Australia. Apparently we have the calm waters and international airport that it needs, amongst other things. Slashdot has covered this company's efforts before: Oct 9, 2002 and, earlier, August 13, 2002, but it's worth discussing again since '[recent funding] has been given momentum by the Columbia shuttle disaster.'"

Comments

It seems like..

[Frank of Earth]

.. only under great circumstances do any modern marvels come to full attrition. Unless there is an actual need, be it military or economic, this project will never "take off the ground"

Basically, it would take some sort of War or space race with China for this to even be the slightest possiblity. Tax payers will not vote for a 17 billion dollar project unless it was under dire circumstances or felt threatened [alla China]

Think about all the previous advances in the human culture. So many were spawned from war. For instance, I doubt the common 747 jet airliner would be such a popular mode of transportation today if the Nazi's weren't looking for a plane that could run circles around the allied air force.

This post is going off in a tangent. I guess what I'm trying to say is that with war comes advancement in technology. Without war, technology is backed by monetary gain. What is to gain by building a space elevator? Unless they can mine diamonds or gold from the upper atmosphere...

Australia?

[djupedal]

What happened to Sri Lanka? I thought the goal was to get as close to the equator as practical.

Not on the equator?

[Michael Woodhams]

I don't understand how they can base it so far from the equator. If you start the counterweight south of the equator, above Perth, it will be way north of the equator 12 hours later.

In more detail:
In a reference frame rotating with the Earth, the counterweight has three forces on it:

Gravity: G m M_earth / r^2
towards the center of the earth
'Centrifugal' force (because we are in a rotating frame): v^2 / r cos l (l = latitude) directed perpendicular to and away from the earth's axis
Tension on the cable.

We want these three forces to cancel out, so that the counterweight is stationary (in the rotating frame.) The problem is that the gravity force has a north/south component unless the counterweight is on the equator. The centrifugal force can't have a north/south component, so the balancing force has to come from the cable tension.

The cable will have be at a small angle to vertical, and the north/south component of the tension is proportional to the sine of this angle, so that component can't be big.

Aha! I think I have the solution.I was thinking of the counterweight being above the tether point.

In the 1st approximation, put the counterweight in geostationary orbit (i.e. on the equator). Run the cable to it.

If the cable had no tension, we would done - but it does. The major component of the tension is towards the earth. We compensate for this by moving the counterweight into a higher orbit. (Decreases gravity, increases centrifugal force, to balance the tension.) There is nothing new here - the Highlift Systems website talks about this.

If the cable was anchored south of the equator, it will have a slight angle to vertical, which will give a southwards force component. If we now modify the orbit of the counterweight to be slightly south of the equator, there will be a northward component to the gravity vector. We can adjust to balance.

From the point of view of the tether point, the cable (if it is straight) will be pointing almost towards the geostationary point. From 30 degrees south, that would be a point about 3000 km north and about 35 km up, so it would be about 5 degrees off vertical.

Energy generation?

[artemis67]

The section of their FAQ that discusses the problem of large electrical currents generated by long space tethers was really interesting...

Would it be feasible to create a tether to low-earth orbit for the express purpose of generating electricity? I wonder how the cost would compare over the long-term to other low-cost sources like wind and nuclear.

Re:Perth not compatible with a geosync orbit

[cpaluc]

I don't get it either. But as some of the other posts have mentioned, it wouldn't be orbiting, it would be getting 'swung' around by the earth.

Would a physicist please correct the following?!

I picture a tether at the equator going out at 90 degrees. If you move down to Perth, the tether will still go out at 90 degrees to the axis of rotation wouldn't it? That is, it would go out parallel to the tether at the equator. See diagram.

X
XX
XXX
XXXX
XXXX---------O equator
XXX
XX---------O perth
X

So, does that mean that it wouldn't be vertical at perth but would go out at an apparent 31 degrees?

Also, does that mean that the thing actually goes over all of the airspace between 31 degrees and just south of the equator? That is, because of the angle, would it actually go over, say, Indonesia's airspace.

Parts of Indonesia are nearly 10 degrees south. Does a line drawn vertically from Indonesia intersect with the ribbon?