NASA proposes using lasers and sweeper spacecraft to tackle space junk

Writing in the journal Science, scientists have called for a legally-binding international treaty to govern the deployment of satellites, taking inspiration from the recently ratified UN High Seas Treaty.

The scientists propose that such an agreement should implement producer and user responsibility for satellites and debris from the time they launch. Also, according to them, the agreement should take into account the commercial costs of these responsibilities and should incentivise accountability.

But not producing any more space junk is only solving a part of the problem. What about the space junk that is already out there? NASA is studying two solutions, and one of them is literally using ground or space lasers.

Using lasers to clear space junk

Lasers can exert force on debris in space without making any physical contact. In its report, NASA focused on two different laser technologies to help manage space junk from a distance—photon pressure and ablation.

Using photon pressure on space junk

With the photon pressure technology, lasers nudge debris to ensure collisions don’t happen. A photon is an elementary particle that represents a “quantum of light,” and therefore, they have no mass.

But while photons are massless, they do carry a small amount of momentum. When a photon (or light, essentially) bounces off an object, it transfers a small amount of that momentum to the object.

The thrust that comes from this method is too little to de-orbit any kind of debris, but it is just enough to help nudge it away from a collision.

Ablation: Using a powerful laser to cut into space junk

With the ablation method, a more powerful laser will be used to strike space debris to “ablate,” or erode it. When this happens, the piece of debris will eject material from one side, generating thrust in the opposite direction and causing it to move. According to NASA, this ejected material will be a combination of hot gas and plasma and should therefore not contribute any new debris to the environment.

Compared to the photon pressure method, ablation requires more powerful laser beams and much higher precision. Simulations conducted by the space agency indicate that this method can be used to de-orbit debris instead of just redirecting it.

Space-based or ground-based laser

If a laser is to be used to tackle space junk, the next step is to decide whether it should be a ground-based solution or a space-based one. One disadvantage with a space-based laser compared to one on the ground is that it will be able to generate much less power because it must produce all that power while in orbit.

But using it also has advantages. One of them is the fact that a space-based laser’s beam will not pass through the atmosphere, meaning it will lose less power. Chances of the beam being deformed are also less, allowing it to be more accurate.

Further, since a space-based laser will be much closer to the debris in question, it will make it easier to accurately target the debris for the intended consequence–-whether it is deorbiting the debris or ablating it.

Using a sweeper spacecraft

If using space lasers to annihilate objects in the orbit is a bit too sci-fi for you, NASA is also considering a concept that is slightly more domestic in its inspiration—using a sweeper.

These sweepers will be large “shields” in orbit that will reduce the amount of space junk by capturing them, slowing them down, or breaking them apart. This method will be especially useful for debris that is too small to be tracked.

Such a sweeper can be made with a variety of possible materials, including aerogels, foams, clothes or fabrics. The material itself might need to be a little supple because otherwise, there is a chance of it sending the debris flying in different directions, exacerbating the problem rather than solving it.

Since NASA is mainly considering the use of such a sweeper solution for small and medium-sized debris that cannot be tracked, they can have either an active propulsion mechanism, or they can move passively. This has to be divided based on how well such a sweeper can manoeuvre away from larger tracked debris while continuing to affect the smaller debris.