Space Elevator: High Hopes, Lofty Goals

Yahoo! News ^ | 9/17/03 | Leonard David

[r9etb]

Wouldn't you want it on one of the poles where it wouldn't spin at all??

The whole idea works because the top of the system is rotating with the earth, just like a bucket on a rope. You need to do it at the equator, because that's the only place you can spin with the earth without wrapping the tether around the ground.

[norraad]

Will there be music in this space elevator?

[r9etb]

On a previous elevator thread, perhaps #23,600, it was shown that the elevator does not need to be anchored at the equator.

Hmmmm. Somehow I doubt that.

[RightWhale]

I doubt that.

I did too. I thought the cable would thrash around and be unusable, but it seems the trajectory is stable and smooth. Shouldn't be a problem.

[LibWhacker]

Yep, you're gonna have to listen to Barry Manilow for seven days straight while you're lifted into orbit. ;-)

[PatrickHenry]

Why can't the thing be "anchored" from a ship? That way we don't need to worry about the political stability of some country. We'd need to worry about weather, of course, but don't we always? Any stuff falling down would hit in the ocean.

(It's probably obvious that I've never really studied the space elevator concept in any detail.)

[jae471]

Just "How close" does it have to be to the equator?

Exactly? +/- 50 miles?

There's an island in FSM about 50 miles north of 0^o that is stable enough, politically. Its about 1200 miles SE of Guam.

Also, there Jarvis Island, 23' south of the equator. Not too far from American Samoa. Its been abandoned since 1957, and is 100% US property.

[LibWhacker]

It didn't gyrate around.

Hmmm . . . I was almost positive I remembered listening to NASA types talk about it at the time. Perhaps it was during the earlier experiment in '92?

I remember because I thought at the time that there were no forces acting on it except gravity, and gravity shouldn't make the end of the cable whip about. Of course, "whip about" and "gyrate" are relative terms; any unexpected movement of the end of the cable is going to cause NASA engineers to get excited.

[RightWhale]

"How close" does it have to be to the equator?

It doesn't have to be anywhere near the equator. Anchor it in Nebraska if you want.

[Flightdeck]

Why does it have to be so long? 62,000 miles is a quarter of the way to the moon!

[r9etb]

I did too. I thought the cable would thrash around and be unusable, but it seems the trajectory is stable and smooth. Shouldn't be a problem.

The problem is that the cable would have to follow a the classic "Figure-8" motion characteristic of a non-equatorial geosynch orbit. The higher the latitude, the bigger the motion.

A moving tether means you're gonna have to drag that cable through miles and miles of atmosphere. That creates drag, of course, and it would be necessary to constantly add energy to the tether to keep it orbital.

You'd also have to figure out a way to let the cable move on its anchor.

[Flightdeck]

"The whole idea works because the top of the system is rotating with the earth, just like a bucket on a rope. You need to do it at the equator, because that's the only place you can spin with the earth without wrapping the tether around the ground."

It sounds like you have it backwards. It's going to be more like a pin stuck in a car tire than a bucket on a rope.

[radioman]

Has anyone computed the static charge of a carbon conductor from ground to a 26,000 mile orbit?

Doesn't sound like a good idea to me.

[RightWhale]

A moving tether means you're gonna have to drag that cable through miles and miles of atmosphere.

Two things.

First, the cable won't move. It will be stable.

Second, even if it did move, it wouldn't move enough or fast enough to generate significant atmospheric drag. The atmosphere is only ten miles deep for practical purposes and the rest of the 22,000 miles to geosynch is atmosphere-free.

[r9etb]

First, the cable won't move. It will be stable.

Say what? How are you going to get that cable up there in the first place? You're going to have to put something in orbit, is how. When you start dropping the line from that geosynch bird, of course it's gonna move.

Now suppose somehow you figure out how to put that thing directly above the latitude of the anchor point. Elementary orbital mechanics says that you're still in an orbit -- how're you gonna keep it from orbiting?

Second, even if it did move, it wouldn't move enough or fast enough to generate significant atmospheric drag. The atmosphere is only ten miles deep for practical purposes and the rest of the 22,000 miles to geosynch is atmosphere-free.

This thing is three feet wide -- try running along holding up a regular newspaper sheet, and you'll understand how much drag a 10-mile long sheet of cable can generate.

And actually, considering the frontal area this thing will present, the drag altitude will be significant well above 10 miles.

For purposes of orbital mechanics, that 10 miles of atmosphere will be plenty -- you're dragging this thing around through the air (probably causing it to twist and flutter, btw), and the drag will need to be made up somehow.

Much easier to just put it at the equator, where the only air you have to move through is the normal old wind.

[RightWhale]

how to put that thing directly above the latitude of the anchor point

Of course you wouldn't do that. The point where the cable crosses geosynch will be fairly close to the equatorial plane, just a little to the same side as the anchor point.

[r9etb]

The point where the cable crosses geosynch will be fairly close to the equatorial plane, just a little to the same side as the anchor point.

It looks like you're telling me that it'll be very near the equator, if not exactly there. If not, I have no idea what you said.

[RightWhale]

The equator is a line on a globe that models the earth and corresponds to an imaginary line on the surface of the earth. The equatorial plane corresponds to that line, which is in fact a circle since the earth is round. The equatorial plane is the one and only plane that would cut the earth exactly in half at the equator, and even more interesting, the equatorial plane is infinitely large so it reaches to geosynch height and beyond. Thus, the anchor could be in Nebraska, which is not near the equator, and the geosynch crossing of the cable would be near the equatorial plane 22,000 miles up.

[stanz]

I disagree...we need to haul as many as possible (lawyers )up to the top...then push them out the airlock!

I love it.

[stanz]

After 9/11, the thought of a structure like this being sabotaged gives me the creeps.