A spacecraft thruster that relies on iodine has been successfully tested in an orbiting satellite ( Nature 2021, DOI: 10.1038/s41586-021-04015-y ). The propulsion system is a form of ion drive, which electrically accelerates a jet of ions to generate thrust. Until now, ion drives—used in space probes such as NASA’s Dawn mission to the asteroid belt—have typically relied on xenon. Xenon’s heavy atoms deliver a lot of thrust, but the element is rare and expensive. It also requires high-pressure storage, which makes it difficult to downsize xenon thrusters for miniature satellites called CubeSats , says Dmytro Rafalskyi, cofounder of ThrustMe , the French company behind the iodine drive. In contrast, iodine is cheap, is abundant, and can be stored as a solid, enabling much more compact thrusters at less than half the cost of an equivalent xenon system. But iodine is also corrosive, so ThrustMe’s system stashes it in a