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 porous aluminum oxide block and uses polymer films to protect exposed metal surfaces. Heaters sublime the iodine, which is then turned into a plasma of I+ and I2+ ions that are accelerated by 800–1,300 V. The 1.2 kg thruster, roughly 10 cm wide, was installed in the Beihangkongshi-1 CubeSat, which launched in November 2020. Trials showed that it performed at least as well as a xenon thruster. Rafalskyi says the smallest satellites sometimes have no propulsion systems at all. The iodine drive would give them the maneuverability to avoid collisions and leave orbit when their work is done, thus preventing the accumulation of space junk.