Sandblast Low Earth Orbit

Space debris are an increasing problem. This was predicted by Don Kessler ( http://webpages.charter.net/dkessler/ ). I thought one solution could be to put active or passive items in retrograde orbit that have cannonballs or clouds of sand hit debris, make them decelerate and reenter the atmosphere.

Don Kessler explained to me that this had already been envisioned and was discarded.

• When two objects with different orbits hit, most of the fragments will go on with roughly the same orbit as their respective parent object. If for example a solar panel of one satellite impacts a part of the other satellite, the place of the impact will be like if an explosive device had been planted there. The explosion will dislodge both satellites, by shrapnel and mechanical shockwaves, but most of the pieces resulting of the dislodging will retain about the same path as their initial object. And each one of them may hit, and dislodge by the explosion, another satellite, or an empty rocket stage... Few debris will be in the right circumstances to decelerate enough to re-enter the atmosphere. Reciprocally, some debris will reach a much higher orbit. And the creation of each swarm of debris in orbit is a catastrophe. Even if an impactor directed on purpose towards a satellite is a compact cannonball that does not become a swarm of debris itself, the target satellite will.
  

• Clouds of retrograde sand targeted at satellites could make them decelerate without having them explode. But the satellites will be "corroded" and slowly dislodged by the impact craters caused by the hyperveloce sand. This will release new debris anyway.

• A "giant cannonball", bigger than the pieces of junk it is targeted at, would indeed vaporize each debris it impacts. But, the cannonball will loose about 1000 times the mass of the impacting debris; each debris will carve a huge crater in the cannonball. It would be technically challenging to ensure that the splinters from the craters do not become space debris themselves... But most of all, to put in orbit 1 ton of impactor for each 1 kg of space junk to eliminate, would make no sense.

• It could maybe work, to send against each space debris a clump of something that will vaporize completely on impact, with a mass comparable to that of the targeted debris. Both the impactor and the debris would be vaporized. But the technology to ensure perfect head-on impacts would be challenging. On the opposite, to send a satellite pursuit the space debris would be much more simple and reliable. Proposals are that the satellite can collect the space debris to feed orbital foundries or it can glue a sail to it that will aerobrake it an speed up its orbital decay. The mass of propellant to pursuit the debris, and possibly the mass of the drogue sail, can be much less than the mass of the debris. A pursuit and catch satellite is much more simple and cost effective than an impactor.
  

• Refined approaches, like have a retrograde satellite or suborbital rocket spew gas towards a satellite to have it decelerate, may work but again the cost of the refinement makes the technique not stand out against other proposals.

• There is no such thing as a killer retrograde orbit in Low Earth Orbit, as most satellites are in polar orbits.

Don Kessler's conclusion is that the only way to handle the cloud of space debris is to stop increasing it. Satellites must include the necessary means to bring them down once their service is over.

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Maybe a solution could be to throw pieces of aerogel at debris, instead of sand. The aerogel, like a gas, would not crater the debris and cause splintering. A retrograde killer satellite may contain the chemicals to manufacture a kind of aerogel. Either the killer satellites can shoot at debris or they can shepherd clouds of pieces of aerogel. The impacted debris would be almost intact but would be braked enough to significantly increase their atmospheric drag and speed up their re-entry.

Peddles of aerogel can maybe also be used to shepherd debris towards defined lanes, where they can be picked up. Shepherd satellites would then be present in all kinds of orbits, in order to be able to transfer the adequate changes of momentum, using pieces of aerogel. In a general way, aerogel is a way to transfer momentum between objects that have different speed vectors. Pieces of aerogel manufactured on the Moon or aside asteroids...


Below are the links to two GIF animations that show the result of a toy numerical simulation to compare the hit rate of a prograde and a retrograde satellite. The green dots are 999 random debris. The white dot is the killer satellite, whose orbit decreases steadily.

http://www.4p8.com/eric.brasseur/sandblast_leo_prograde.gif

http://www.4p8.com/eric.brasseur/sandblast_leo_retrograde.gif