Using Lasers and Water Guns To Clean Space Debris

WSJdpatton writes "The collision between two satellites last month has renewed interest in some ideas for cleaning up the cloud of debris circling the earth. Some of the plans being considered: Using aging rockets loaded with water to dislodge the debris from orbit so it will burn up in the atmosphere; junk-zapping lasers; and garbage-collecting rockets."

Comments

Water????

[Muad'Dave]

Not only would lofting water into space be a colossal waste of energy and water, it would only exacerbate the problem!

IMHO the only 'clean' way to deorbit debris is to add energy to the debris in the retrograde direction without using additional mass, which means photons. Laser pulses could do it either by radiation pressure directly (huge laser), or by pulses that ablate the debris slightly (creates tiny beads of additional debris).

Electron/proton beams would work as well, as would alpha particles, but they'd pose a risk to humans in space. In fact, using charged particles might induce a charge on the debris that would then help direct the debris toward it's doom (debris vector, Earth's magnetic field, right hand rule....whatever).

PlanetES

[psergiu]

http://en.wikipedia.org/wiki/Planetes

Re:How do you pull with a push?

[icebrain]

Orbital mechanics work in strange ways. For example, in a circular orbit, you don't thrust up to go up, you thrust forward. Going down, you thrust backward.

In this case, your best bet will be to hit the forward side of the object. If that's not possible, then hitting the bottom of it (depending on where it is in the orbit) will also have an effect. I can't remember offhand what happens from in-plane radial delta-V application, but I think it's a combination of changing the eccentricity of the orbit without affecting the total energy, and changing the longitude of periapsis. Sorry, it's been a couple years since I took orbital mechanics...

Now if you get a space-based laser up, you get more freedom in how your burns are applied.

Re:Ok, now serious, really

[drinkypoo]

Doesn't work. The impactors will just break loose pieces of the ice. There has been some thought put into using Aerogel, since it has density low enough to not explode when hit by something going very. fucking. fast.

Re:Water is heavy

[JumboMessiah]

True, most only really think of oil as being the next big thing to cause mass hysteria, but few realize that potable water is a dwindling resource in certain regions. Even the giant Ogallala aquifer in the central United States is showing increased rate of depletion (not to mention pollution).

There are a few books on the subject.

Something doesn't seem to add up

[Rival]

Something doesn't seem to add up. They've already indicated that slight modifications to trajectories can deteriorate an orbit, so some portion of the space junk caused by collisions must fail to remain in orbit. But they also say that collisions cause more junk, which causes more collisions, as though this were a never-ending cycle of feedback.

It seems as though there must be a threshold somewhere where the introduction of further space junk removes from orbit, on average, an equal amount of debris as it introduces. The farther past this threshold, the more likely that introducing debris will remove more than is introduced. There must be a point of equilibrium.

Take the following exaggerated scenario, for example. Let's say that by chance or plan, there is debris in orbit within every cubic meter at stable altitudes. (I am not a physicist, but this seems highly improbable statistically.) The introduction of a meteoroid through this debris field would almost certainly cause a significant chain-reaction with many affected objects acquiring unstable orbits leading to failure.

Not-to-scale pictures aside, I doubt we're anywhere near such a threshold -- even if we are reaching a point where our ability to avoid debris is insufficient to mitigate the danger. But surely it would be at least interesting, if not practically useful, to know this "saturation" point.

Or perhaps this is already known, and I am just unaware.

Re:Something doesn't seem to add up

[Rival]

This is a good point. But as collisions become more and more frequent, I don't think they be able to maintain momentum. The energy from each collision is spread out among all the fragments produced, and also some is lost during the impact as heat and the energy required to separate the fragments from the larger original pieces.

Let's say that "first-generation" objects are on a stable orbit with sufficient momentum to maintain orbit. After impact, some of the resultant second-generation fragments will fail orbit quickly due to grossly incorrect trajectories, while others enter trajectories that will take longer to fail. Over the time it takes for these second-generation fragments to fail, they cause more impacts. More of these third-generation fragments are lost more quickly, and the remaining ones proceed to cause fourth-generation impacts, and so on. This is the general chain-reaction idea being posited.

One factor to consider is the fact that as these particles reach higher "generations", they are in more and more grossly failing trajectories due to either bad vectors or insufficient momentum. These trajectories intersect less and less with stable orbits, so the collisions are more and more likely to be with already-failing particles. This could only accelerate the orbit failure. Essentially, these particles should clean themselves up.

Again, I am no astrophysicist, but it seems that if chance supported easily-achieved orbits, then we would already be at saturation. The fact that we're not suggests that the "random collisions creating a permanent* cloud of debris" theory may not be self-supporting.

Of course, it may be that the time it takes for this debris field to fail is on a scale which is inconvenient to us. But to say that we'll eventually end up with a stable cloud of microscopic bits just doesn't add up.