# Impact of space junk on Earth based space elevators

It is well known there is a lot a space junk orbiting the Earth. From previous questions posted on this site it appears that if it were possible to establish a space elevator cable for Earth it would have to be very long. Also, it would need to be placed through the space junk zone orbiting the Earth.

In such a situation could impact by space junk/debris be serious enough to make a space elevator impractical?

• The worst case is a satellite hitting the elevator. Would you want that? Commented Aug 18, 2015 at 12:21

## 2 Answers

The space elevator basically consists of a base station that acts as an anchor, a long cable for movement of 'climbers' and a counterweight to keep the cable in place.

The length of the cable is determined by the intended purpose. Below the altitude of geostationary orbit (~ 35,786 km), the gravity is more than the centrifugal force and above that the centrifugal force is more than the gravity.

Source: Wikimedia Commons: User:Booyabazooka

A space elevator constructed as shown above will pass through the atmosphere, the earth satellite orbits and the Van Allen radiation belts.

The debris in the low earth orbit is but one of the hazards faced by the space elevator. Aircrafts, meteorites and orbiting satellites all can potentially snap the cable.

It is possible to design the satellites so that they avoid the cable(of course you would have to replace every one out there). The orbital debris is another thing.

There are about 6000 tonnes of space junk in orbit and most of them are in the LEO orbit.

Image Source: NASA

There are more than 21,000 orbital debris of diameter 10 cm or more in orbit, which can cause serious damage to the cable as they usually travel in speeds excess of 10 km per second.

Considering the fact that the elevator cable will be practically stationary and the very high number of debris in orbit, it is certain that one of them will hit the elevator cable.

In that case, the cable will snap and more importantly, the counterweight will simply fly out of the earth orbit. Considering the probable impact height (~1000 km) and the total cable height (>36000 km), the entire system will have to be rebuilt again.

This is a serious safety issue for the vehicles using the space elevators during that time as well as they most probably will not have a propulsions stem of their own (this being the most important advantage of space elevator)

In conclusion, the safety of the elevator cable from impacts is one of the most important challenges that has to be solved if the system is to become practical.

• "as they usually travel in speeds excess of 10 km per second." A 300 km altitude orbit moves about 7.7 km/s. Higher orbits are slower. To get over 10 km/s at a 300 km perigee, you'd need a 30,000 km apogee. I wouldn't call a 300x30,000 km orbit "low" Commented Aug 20, 2015 at 15:52
• "the counterweight will simply fly out of the earth orbit. Considering the probable impact height (~1000 km)" The lower 1000 km of an elevator is a small fraction of total mass. Cutting it would have some impact on the elevator, it'd rise to a slightly higher orbit. But it wouldn't achieve escape. Commented Aug 20, 2015 at 15:58
• I was going to say the same thing as @HopDavid, a low break is not an insurmountable problem. A new segment could be attached, and lowered back down to Earth, and the elevator pulled back down into position. The worst kind of break would be below the counterweight, as then the counterweight would fly away, and the cable would fall down to Earth. Commented Aug 21, 2015 at 12:35
• Rising to a higher, slightly slower orbit would put the bean stalk on a slow collision course with geosynch sats having 0º inclination. Commented Aug 21, 2015 at 13:06
• There is a band of orbital debris just above geosynch - the graveyard orbit for geosynch sats. This band of orbital debris 300 km above geosynch would be moving about 35 mph with regard to a bean stalk. A dead sat cutting the stalk just above geosynch might create the awful scenario @BlakeWalsh describes. Commented Aug 21, 2015 at 13:17

I've been thinking about this very thing for some reason. I think, in terms of engineering and feasibility, cleaning up all that debris would be simpler than building a space elevator. So I don't think this is really all that big of a deal.

But, supposing for whatever reason we do not clean up LEO (or to protect it against any case) I'd think large sections of the elevator would have to be radiation shielded, especially where it passes through the van allen. We're also most assuredly needing electricity to course through the thing, so I suppose we could 'kill two stoned birds' by embedding or paralleling the elevator with superconducting material and sending a charge through it. I just don't know how much we'd need produce a magnetic field big enough to, not only shield from rads, but deflect incoming debris as well.

One of the gundam plots was centered around vast photo-voltaic power plants in orbit, connected to the earth by such elevators. This could also necessitate the superconducting core. My point is, I'm sure if we ever got around to building the damn thing, a solution will be generated almost implicitly.