Boeing has filed a patent for a method of disposing of dead satellites and other debris orbiting the earth by hitting them with a puff of gas. The method, which is still at the conceptual stage, is designed to slow down satellites, forcing them to re-enter the atmosphere without sending up more space junk that itself will need disposing of.

On February 10, 2009, one of the worst nightmares of space travel occurred. At 789 kilometers (490 mi) above the Earth, the Iridium 33 and Kosmos 2251 satellites collided at hypersonic speed, spraying thousands of pieces of debris into space – each one a potential hazard to spacecraft or astronauts. In the 55 years since the launch of Sputnik, thousands of satellites have been launched into orbit and they, along with their boosters and assorted bits, pose an increasing risk of more collisions spewing more debris resulting in more collisions.

Over the years, many solutions have been proposed for getting rid of all that orbiting rubbish. There have been plans for grappling satellites, harpoons, solar sails and even balloons. The only problem is that most of these ideas involve launching more satellites into orbit, rendezvousing with the dead satellite or other debris, latching onto it and then either dragging it back to Earth or shooting it somewhere safe in outer space. That is very complicated, expensive and risks putting even more debris into orbit while cleaning up what’s already there.

The Boeing patent filed by inventor Michael Dunn suggests that the alternative is to use what is called “ballistic gas.” The idea is to send a small satellite into orbit containing a gas generator. This generator can be a tank of cryogenic gas, such as xenon or krypton, or a device designed to vaporize a heavy metal or some relatively heavy elements like fluorine, chlorine, bromine, or iodine. This gas would be released as a cloud in the same orbit as the debris, but traveling in the opposite direction.

The cloud wouldn't last very long, but long enough to hit the debris. By the time it hit, the gas would have expanded until it was almost a vacuum, so it wouldn't damage the debris. In fact, an astronaut caught in such a cloud probably wouldn't even notice it. However being hit by “almost” a vacuum at hypersonic speed is enough to slow down the debris and cause its orbit to decay until it hits the atmosphere.

The beauty of using ballistic gas is not only that it’s mechanically simple and that it doesn't require contact with the debris, but that the gas cloud doesn't even need to be aimed with any precision. All that’s needed is to point the generator in the general direction and let go the gas. For larger satellites or those in higher orbits, multiple puffs can be used to bring it down. Additionally, the gas satellite can be used to take down multiple targets in different orbits, so only a few such satellites would be needed for a clean-up program.

Source: US Patent Office via New Scientist