In a recent e-mail exchange with my friend Kurt, we were discussing the problem of orbital space junk and the difficulty of cleaning it up. It’s a subject we’ve batted around on and off for many years, wondering about a workable and economical solution but never managing to find one. It’s been in the news more lately, as the crisis has grown more acute and inventors have trotted out different proposals, each more outlandish than the last.

In the middle of this exchange, after years of coming up with nothing, I suddenly invented my own solution, an idea I now offer publicly as the second in my occasional save-the-world series. It’s called SIEVE: Scanning, Illuminating, Even Vaporizing Engines.

It involves deploying into low earth orbit thousands of semi-autonomous robots. Each SIEVE unit is small and light and costs no more than a few hundred dollars of off-the-shelf components. Specifically, these components:

  • A solar panel for power;
  • Gyros for orientation;
  • A radio for coordination with other SIEVE units;
  • A camera;
  • A simple computer;
  • A Mylar mirror; and
  • A small rocket engine.

Each unit, when in sunlight, is in one of three modes: Scanning, Illuminating, and Vaporizing.

In Illuminating mode, the unit orients itself so that the mirror reflects sunlight through a given volume of space.

In Scanning mode, the unit trains its camera on a region of space that other nearby units are Illuminating and searches for debris.

In Vaporizing mode, numerous units all aim their mirrors to shine sunlight on a piece of debris, one previously identified by Scanning and Illuminating units and whose orbital trajectory has been plotted. Focusing enough sunlight on the debris for a long enough time should heat it to the point of vaporizing. If the debris can be fully vaporized, great; it should be harmless in that form. If it can’t, it might still expel enough vapor to slow its orbit (a la the laser broom idea) to the point where it falls back into the atmosphere.

The rocket engine is only needed twice: once to insert the unit into a distinct orbit when initially deployed, and once to deorbit the unit at the end of its service life.

Care will have to be taken that the SIEVE robots do not themselves become hazards to space navigation. And that they don’t go into Michael Crichton mode, become sentient, and decide the Earth is a gigantic ball of debris.

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