Don't Mine Orbital Debris

Expanding into space is an expensive and complicated endeavor. One of the many factors that contribute to the challenges for designing space missions comes from orbital debris. The wrong piece of debris, smaller than a paper clip (0.65grams), hitting the International Space Station will have the same kinetic energy as a .50-caliber bullet. That’s enough energy to really mess up your day. As the number of active satellites grows the risk of catastrophic collisions will grow. To the armchair engineer it might seem so obvious, why don’t we get a giant machine to suck up all that debris? You could kill two birds with one stone, remove debris and provide feedstock for making future space missions. What we will cover in this post, in a bit of detail, why this is a bad idea. (to be clear I’m talking about clearing up items smaller than a shoe box, for larger orbital debris there are far more legitimate re-use, recycling, and decommissioning strategies being developed.)

It comes down to viable technologies and material density.

Idea 1) What your5 year old nephew suggests while high on sugar would come up with, a giant vacuum.

Space is already a vacuum, and the way vacuum cleaners work here on Earth is by creating a pressure gradient to pull stuff along. In space you already have one of the hardest vacuums you might possibly imagine, so creating a pressure gradient would be insanely difficult for any distance.

Idea 2) Large magnets

Most orbital debris come from metallic spacecraft so why can’t we use a giant magnetic field to pull debris towards a collection site. Less problematic than our vacuum as a magnetic field can certainly be generated, unfortunately a magnet that would be strong enough to even have a prayer of pulling up debris, is also likely to be strong enough to disrupt satellites. That means that unless you can perfectly turn your idealized magnet on and off you’re likely to mess with someone else’s fully functional satellite. This is bad because if you mess with the wrong satellite, you have committed an act of war.

Idea 3) Grab things directly

Most physically doable, downside, is you have to physically touch each piece of debris, which given the volume of space, not realistic for small items by any kind of realistic time scale (check the density bit down below for a clearer explanation)

Idea 4) Plasma Tractor Beam

This idea is only likely to have come up if you are already really in the space environment space. Basically, there is a proposal to create an orbital debris clean up satellite that emits an ion beam at a targeted piece of space debris. By changing the ionization properties of orbiting debris you can subtlety redirect their orbit. In theory you could use that to change the orbits enough to reach a more useful collection location. (Maybe, but probably not)

And now for the details I alluded to earlier, no matter which idea you choose, or independently come up with unless you are an alien civilization with proven access to far more energy/technology/understanding of physics, than what humans see on the foreseeable horizon, collecting small space debris for construction is a terrible no good very silly idea.

The density of material in Earth Orbit isn’t big enough to bother trying to actively collect the small stuff. If we imagined that surrounding the Earth there was an evenly dispersed collection of fine dust that had the same mass as all of the ice of the Greenland Ice-Sheet (as I read Wikipedia 2,900,000 Gigatons) (and this is so not realistic). Let’s pretend that this dust swarm is only found from 100km above the Earth’s surface to 600 km. Our dust cloud would at best, have a density of 0.0102 kg/m^3 or 1/120th of the density of air.

Now imagine how difficult it would be for our theoretically clean-up system to evenly remove this debris, and how much energy it would take. In the near term you are better off simply making sure your spacecraft are tough enough to survive random impacts, and when you are nearing the end of your mission, move your satellite into a path that will either cause it to burn up or simply be too out of the way for it to be a risk to future missions.
Longer term we will need to clean up the debris orbiting our planet. For larger debris, it can make sense to capture and recycle old spacecraft. For the flecks of paint and bolts other approaches should be considered, like lasers (note to self add a link to my argument for using orbital laser platforms to clear out debris)