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
- 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.
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.
Eric Brasseur - May 29 2012
till August 14 2013