h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Let's assume that the engineering and technical requirements are met some time in the not too distant future. We are able to build a tethered satellite or space elevator.

What about all those other tens of thousands of satellites (and bits of satellites) already in orbit? Sky hooks by definition are geostationary and thus based on the equator. Their termini are beyond the normal geostationary orbital altitude to keep tension on the tether. So, obviously there is no threat from geostationary satellites. Also, any satellites with an orbit that is periodically linked to the earth's rotation will be less of a threat as their ground tracks are such that they pass over the equator at the same longitudes predictably. But what about satellites that aren't in a periodic rhythm with the earth's rotation? Won't they all eventually intersect the vertical column of the sky hook's tether?

Have we effectively made them... Is pre-obsolete a word? No, it's not... non-feasible?

I'd imagine that the economics of building one would be such that getting rid of all the satellites that could hit it would be pretty cheap. Not sure about debris right enough.

All the satellites at less that geostationary height will pass over every point on the equator at some stage, so they'd all have to be removed.

""All the satellites at less that geostationary height will pass over every point on the equator at some stage,""

how long a line is the equator at less than geostationary height???

how wide will the tether be??

how wide is a satalite

i think we have a needle in a haystack collision senario here

the addition of a little extra fuel and some adjustment thrusters might become the norm for satalites, so they dont hit the tether

could there be some sort of magnetic shield on the tether to deflect potetnial impacts

The tether would be likely to be only about 30 cm across. A satellite is about 1m, I think. So the satellite could go around the world thousands of times and miss the tether each time, but it would be bound to hit it eventually.

But most of the things we need satellites for could be done quite easily from a few geostationary points.

unless the satalite is 'not realy there'

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""Are sky-hooks still even theoretically feasible""

ask any new recruit in the armed forces!!!!!

many are sent every day to the guardroom or the stores to collect sky hooks

they are kept in the same cupboard as the tartan paint, right next to the keys for the indoor grenade range

Gnomon, you're seeing what I'm seeing. Every satellite with a non rhythmic period will cross any given equatorial point at its altitude eventually.

Keep in mind there are many satellites that are no longer in controlled orbits and even more pieces of orbital debris. Even satellites currently in controlled orbits will experience orbital decay. This will eventually result in that satellite intercepting any geostationary tether.


I grew up dreaming of Arthur C. Clark's vision of an Earth tethered satellite, but I now can't see how it's feasible.

http://en.wikipedia.org/wiki/Kessler_syndrome It's even worse than we thought.

I think we'd have to release a cloud of nanobots, whose job would be to seek out orbital debris and stick to it, then fire microrockets to alter its orbit, moving it down to the top of the atmosphere, where it would burn up. When all the debris is gone, you could recall the nanobots... except that many of them would have run out of power and would be debris themselves. Thorny problem...

the nonobots idea is a good one, they don't fire rockets just reduce the debris to dust(bite, bite, bite), we then mine the dust with a couple of buzzard ram scoops fixed to the tether

Or fit thrusters to various parts of the skyhook... Move IT out of the way, doesn't have to be the whole lenght of it at once...

One of Mars's moons orbits below the geostationary height. Somebody suggested that a space elevator on Mars would need to sway to the left and right to avoid the moon. You could set it to vibrate like a giant guitar string, with the vibrations timed to avoid the moon, which is after all predictable.

It wouldn't be so easy to avoid random debris.

What we need to do is put a bulldozer in orbit, which can scoop up all the space junk.

A giant glue-ball.

Here's a totally random idea. Back in '96 they did a tethered satellite experiment. http://www-istp.gsfc.nasa.gov/Education/wtether.html A cunductive tether was extended out from the shuttle with a small satellite at the end of it. As the tether moves through the earth's magnetic field it creates an electric current. It also creates drag due to the electromotive force induced by the current. Maybe an array of small autonomous satellites could be deployed that would seek out dead satellites an debris, attach to them and deploy tethers. The EMF induced by the tethers would degrade their orbits and bring them down. Now more cotrollable methods would be needed for larger satellites to avoid UARS type debris that is big enough to avoid burning up on reentry, but it might work for small satellites.

I really want an edit option.

A space shuttle dragging a large net might be an idea. Then they can harpoon the larger pieces.

This is an estimate of the growth of the debris "ring", over time, by ESA.

http://www.esa.int/esaMI/ESOC/SEMN2VM5NDF_mg_1.html

Don't know if there's enough netting, and certainly no more space shuttles. Interesting discussion, though. BTW, Count Zero, am I correct in thinking that geostationary orbit is ~22,000 miles? That's one heck of a long tether...with many multiple layers of space debris orbiting below it.

Yep. Or about 35,786 km. And a space elevator would be even higher than that.

The idea of just launching a "net" doesn't work for a couple of reasons. It wouldn't be stationary, sitting in one place capturing debris like a fishing net across a river. Although I suppose you could put on in a retrograde orbit. But anyways, the velocities of colliding debris would require a material that could withstand unthinkable impact forces otherwise the net would just result in even more debris as collisions break of piece of it.

As to nanobots, I can't see how they could maneuver between objects. By definition they are tiny. What would be their method of propulsion?

I seem to remember an 80's TV show in the US where an enterprising family built their own shuttle and did business as space garbage men or bin men, retrieving space junk. That might be the most feasible solution is to somehow make it worth commercial interests to clear the debris. A profitable solution might be found that way.

The space elevator needs to extend to about twice the geostationary height for balance.