Description: Colloid thrusters have long been known for their exceptional thrust efficiency and ability to operate over a range of specific impulse due to easily variable charge-to-mass ratio of emitted particles. They have also been considered limited to only very low thrust levels, able to produce few microNewtons from individual emission sites. This has motivated significant research into developing large microfabricated arrays of emitters in order to achieve greater thrust. Busek, using an alternate approach, avoids the complications of large emitter arrays while obtaining about 2.5 milliNewtons/cm2 and about 13,000 emission sites/cm2, and has proven this at the 0.1mN thrust level for over 450 operating hours. Combined with colloids' variable Isp capabilities and thrust/power superior to other electric propulsion devices, these new, high thrust colloid thrusters promise to enable new classes of missions benefiting from variable Isp of 200-5000s (or greater) and variable thrusts up to and exceeding 20mN. For the Phase I effort, Busek shall perform a proof-of-concept demonstrating scalability of its proven 0.1mN, cylindrical emitter into a swept linear or annular configuration (to increase emission area while preserving the cross-section), resulting in a 5mN prototype. For the subsequent Phase II, the emitter will be scaled up to 20mN and packaged and tested with fully integrated propellant storage/feedsystem and electronics.

Benefits: The primary non-NASA application for the proposed thruster is to support development of colloid-based multi-mode propulsion using green monopropellants, where there is a lack of suitable thrusters at the milliNewton level or greater. This allows a spacecraft to utilize shared propellant tanks for high thrust chemical propulsion as well as high Isp electric propulsion, and is particularly attractive for small spacecraft with limited mass and volume for multiple propellant tanks. Additional applications include replacement of some of the lower thrust plasma-based electric propulsion devices, which suffer from decreased efficiency at low power due to unfavorable surface-to-volume scaling. The variable Isp capabilities and higher thrust levels provide a useful multimode solution for spacecraft requiring both dwell/stationkeeping as well as rapid maneuvers from a single propulsion system.

Primary NASA applications include missions requiring exceptional thrust/power in power-limited missions, and missions benefiting from variable specific impulse (200-5000+seconds) and throttleable thrust (10x throttling). In many cases, the proposed colloid thruster may prove superior to most other electric propulsion technologies in nearly all metrics for power levels <200 Watts (where thruster efficiency has greater impact on total system efficiency).