More on Space Elevators

finally writes "Space elevator news is being reported on Space.com and Yahoo. I, for one, am really excited about the project. I was wondering if any of the broad range of talents and skills that we have here have thought of doing a sort of open source assistance to this project by means of donating time and knowledge." We did a big story last week on this space elevator conference.

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Re:What happens when the cable breaks?

[shrikel]

Actually the cable is more like 60,000 miles long. The idea is to use a substance that will NOT break easily. And if it did break, it wouldn't crash down like steel, it would float down like paper. They're taking this into consideration. Look at their faq on their website.

Re:What happens when the cable breaks?

[the_skuncle]

More fiction and speculation has been written on this subject than you could throw a stick at.

K.S. Robinson blew the counterweight off of his space elevator in his awesome mars series, and it encircled the equator almost three times. By the time it was almost completely down, the heat from re-entry and pressure of impact caused the carbon whiskers to turn into pure diamond and bucky-balls (Buckminster Fullerenes).

Now, sure I know that it is only fiction, but so was 'Twenty Thousand Leagues Under The Sea' when it was written.

I also read a crappy book that placed the elevator on the polar axis instead of on the equator. It was written by some famous British guy who had written piles of stuff for Dr. Who and Red Dwarf among others. It answered the nagging question as to why I hate TV Science Fiction; There's virtually no science involved at all.

Just my $0.02

Re:Why do they have to hang straight down?

[WolfWithoutAClause]

But, the one thing that has always bugged me has been why the cable itself has to hang straight down from orbit.

The trouble is that the combination of rotation (which pulls at 90 degrees to the axis of the earth) and the earths gravity (which pulls directly towards the earths center)- the combination ends up pulling the end weight so that it is above the earths equator. The cable below that goes from the attachment point on the earths surface up to there.

You can move the endweight only a small amount from the earth end- the radius of the earth is only 6700 km, but GEO is 38000km, so the geometry for moving the end weight around doesn't add up.

So basically, the endweight is in the plane of the equator. So the cable comes off at an angle from the earths surface- and heads off to the weight beyond GEO. At the equator the angle is 90 degrees. But as you go north or south, the angle is lower, and the angle means that the tether is longer and weighs more, as it droops under gravity (there's little rotation force at low altitude to compensate, so it does it quite a lot.)

So if you go very far north you find that the cable leaves the earths surface horizontally... there's no point in going further north than that. Exactly how far north this happens depends on how heavy the cable is, and how much tension there is in the cable at ground level. So you can increase the tension and pull it up off the ground again. But by doing so, you are losing payload by doing this- the extra tension to make this work could be used to lift payload up the tether.

It's a bit oversimplified, but that's the main idea. You can do it, but it's probably not worth doing it.