Miniature Ion Thrusters for Precision Formation Flying

Miniaturized ion thrusters are attractive for precision formation flying and many other future space missions. Their potential for high-efficiency and low-noise operation provides the mission designer with a uniquely attractive option in the mN thrust range. Caltech and JPL have designed and tested a small, 3 cm diameter ion thruster that demonstrates propellant efficiency > 80% and Isp > 3100s using a cathode generated xenon discharge. These investigations have shown that desirable discharge confinement efficiency is possible with reasonably sized magnets, and consequently low overall thruster weight. Robust, long-life ion extraction grid geometries were designed using computational tools and have performed well during experimental testing. Several flight-worthy cathode designs are currently under investigation for the neutralizer and discharge cathodes. In particular, recent design efforts have focused on miniature hollow and direct emission cathodes. Direct emission cathodes using hexaboride emitters are being considered for their applicability to precision formation flying missions, fast cycling times, scalability to even smaller thruster sizes (<3cm), and ability to run with low-purity propellants. Early testing of a direct emission LaB6 cathode has shown that such a cathode can provide good overall performance if consistent cathode heater performance can be maintained. Future testing will focus on the design and validation of efficient, flight- worthy cathodes and demonstration of thruster lifetime.