Aerospace giant Boeing has developed a novel means of clearing space junk from low Earth orbit: A cloud of ballistic gas. Most space junk-clearing schemes involve launching something up there to physically de-orbit debris, but this means launching rocket stages into orbit that then become more orbital debris. Boeing's solution: Launch a rocket full of cryogenic inert gas right to the very edge of space, then forcibly eject tons of vaporised gas further upward into an orbiting debris cluster. The initial density of the cloud will create enough drag to slow the debris just enough to de-orbit it, and the launch rocket would remain low enough to fall harmlessly back to Earth.