The Dawn space probe was the first unmanned vehicle to orbit two distinct planetary bodies (4 Vesta and the dwarf planet 1 Ceres), despite the loss of two of it's four reaction control wheels and a reboot. Powered by a 10 kW solar array, the probes 3 ion engines work by expelling xenon gas at a significant fraction of the speed of light. Like nearly all unmanned space probes, Dawn will cease functioning due to the loss of funding or mechanical failure, though with a small consolation: the stable orbit of the probe means it will likely become a permanent satellite of Ceres. As a tangible object Cormac is an totem to wanderers and travels without destination.
The use of ion engines in spacecraft dates to the first SERT engines debuted in the mid 1960s. Early prototypes were demonstrated by Ernst Stuhlinger, assistant to Warner Von Braun's space program during the Third Reich. Recovered by the U.S. Military during Operation Paperclip in the closing days of World War 2, Stuhlinger would go on to a long career in the embryonic NASA heirarchy, notably working with the Walt Disney Corporation as a technical consultant on animated films during the 1950s, and hand triggering(!) a staging timer on Explorer I, the first U.S. satellite. His spare time was spent on electric propulsion systems for spacecraft, which he called "sunships". These early experiments, expelling mercury vapor as propellent, exist as the progenitors of the current ion engine technology.