Abstract
In order to send a spacecraft to a near-earth small body such as a comet or an asteroid, high-Isp electric propulsion based on the solar electrical power (usually called SEP) is very attractive because SEP can realize faster mission trip time with a smaller spacecraft and a launcher, which cannot be accomplished with conventional chemical propulsions. For the asteroid sample and return program promoted by the Institute of Space and Astronautical Science, a 1kW-class ion engine system is used. Adopting the ion engine that features high Isp around 3,000s and high thrust efficiency 30-40%, such an ambitious mission can be realized by a relatively small satellites weighing 450 kg with a medium-class launcher, Japanese M-5 rocket. The newly designed engine features microwave discharge, which is free from degradation of the thermionic cathode ordinarily used for conventional type ion engines, hence, very long lifetime required for the sample and return mission becomes possible. An engineering model of the thruster head was fabricated, and its thrust performance, thermal design, mechanical design, and lifetime of more than 13,000 hours were successfully demonstrated.
