Propulsion is a critical subsystem of many spacecraft^1,2,3,4. For efficient propellant usage, electric propulsion systems based on the electrostatic acceleration of ions formed during electron impact ionization of a gas are particularly attractive^5,6. At present, xenon is used almost exclusively as an ionizable propellant for space propulsion^2,3,4,5. However, xenon is rare, it must be stored under high pressure and commercial production is expensive^7,8,9. Here we demonstrate a propulsion system that uses iodine propellant and we present in-orbit results of this new technology. Diatomic iodine is stored as a solid and sublimated at low temperatures. A plasma is then produced with a radio-frequency inductive antenna, and we show that the ionization efficiency is enhanced compared with xenon. Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation. The propulsion system has been successfully operated in space onboard a small satellite with manoeuvres confirmed using satellite tracking data. We anticipate that these results will accelerate the adoption of alternative propellants within the space industry and demonstrate the potential of iodine for a wide range of space missions. For example, iodine enables substantial system miniaturization and simplification, which provides small satellites and satellite constellations with new capabilities for deployment, collision avoidance, end-of-life disposal and space exploration^{10,11,12,13,14}.

推进是许多航天器^1,2,3,4的关键子系统。为了有效地使用推进剂，基于气体电子碰撞电离过程中形成的离子静电加速的电力推进系统特别有吸引力^5,6。目前，氙气几乎完全用作空间推进^2,3,4,5的可电离推进剂。然而，氙气很稀有，必须在高压下储存，商业化生产很昂贵^7,8,9. 在这里，我们展示了一个使用碘推进剂的推进系统，并展示了这项新技术的在轨结果。双原子碘以固体形式储存并在低温下升华。然后用射频感应天线产生等离子体，我们表明与氙气相比，电离效率得到提高。原子和分子碘离子都被高压栅格加速以产生推力，并且可以产生具有大量碘解离的高度准直的光束。该推进系统已在太空中搭载一颗小型卫星成功运行，并使用卫星跟踪数据确认了机动情况。我们预计这些结果将加速航天工业中替代推进剂的采用，并展示碘在广泛太空任务中的潜力。^{10,11,12,13,14}。