A Compact Low-Power High-Isp Thruster for Microsatellites

Busek Co. Inc. completed delivery of flight-qualified colloid thrusters for NASA’s ST7 mission in May 2008. This effort has led to development of variants of the technology suitable for small satellite applications. Colloid thrusters operate by electrostatically accelerating charged droplets of an electrically conductive ionic liquid, and are capable of providing a high degree of throttling and variable Isp. Life tests of the ST7 thrusters have demonstrated over 3000 hours of continuous operation with no deterioration in performance. A further benefit is that the colloid thrusters do not present high pressure and fire safety hazards common to many other propulsion systemsthe propellant is nonreactive and is typically stored at less than 20psig. The thrusters presented have a target maximum thrust of 1 milliNewton with 0.1-1.0 milliNewton throttling. They are designed to operate in the Isp range of 400-1000s, consume a maximum of 15W (including power supply losses), and be self-contained in a 10cm x 10cm x 20cm package requiring only power and thrust command inputs. The package contains sufficient propellant for 500 hours operation at maximum thrust, yielding total impulse of 1800 seconds capable of imparting almost 200 m/s delta V to a 10kg satellite.