Electric Propulsion Microthrusters for Spacecraft Precision Pointing and Attitude Control

Abstract:
This talk will focus on the different applications for precision microthrusters on spacecraft position and attitude control, including the flight experience of ST7 and some recent results of performance studies looking large-scale observatories.

Precision microthrusters have been operated successfully in flight, providing drag-free and precision control for spacecraft that can be used for future applications such as gravity wave and exoplanet observatories. The Space Technology 7 Disturbance Reduction System (ST7-DRS) technology demonstration payload included eight Busek Colloid Micro-Newton Thrusters (CMNTs) as part of the Laser Interferometer Space Antenna (LISA) Pathfinder mission that launched in December of 2015, which also included European cold gas microthrusters. The CMNTs provided full attitude and precision drag-free control of the spacecraft with 10 nm/√Hz stability along the most sensitive axis during commissioning, nominal, and extended mission phases through April of 2017.

Performance requirements (≤0.1 µN/√Hz) were met and models were validated based on on-orbit measurements of test mass motion and actuation during the 60-day nominal and 30-day extended missions. In 2018, the European Space Agency (ESA) selected LISA to be the agency’s next “large-class” mission, currently in Phase A, with a launch scheduled for 2034 and a 12.5-year duration. NASA is considering a significant contribution of hardware to the ESA-led mission, potentially including colloid microthrusters. In preparation, NASA is developing five technologies to TRL 5 and 6, including the colloid microthrusters, to be ready for infusion into LISA.

The Habitable Exoplanet (HabEx) observatory mission concept also might require precision microthrusters for attitude control, replacing reaction wheels with worse pointing performance. In this case, using colloid microthrusters have been shown to meet the tight pointing requirements necessary to image Earth-like exoplanets around nearby stars. Future Earth-orbiting gravity-measurement missions, similar to GRACE, are also considering atmospheric drag-free operation to improve resolution.