Low Impulse Bit Electrospray Thruster Control

Busek proposes to develop a new form of passive electrospray thruster control which will enable extremely fast thruster operations and thereby unprecedented minimum impulse bits. Busek’s BET-300-P thruster is under active development as a precision reaction control system (RCS) which will provide orders of magnitude improvements over state-of-the-art alternative attitude control systems (ACS) for CubeSats and small spacecraft. The low inertia of CubeSats combined with vibrational disturbances and resolution limitations of state-of-the-art ACS presently limit precision body-pointing and position control. Busek’s electrospray thrusters aboard the ESA LISA Pathfinder (NASA ST-7) spacecraft, recently demonstrated control of a proof mass location to within ~2nm per root Hz over a wide band. The BET-300-P, enhanced by exploitation of its high-speed dynamic response in this program, seeks to extend that success to small spacecraft platforms.Passively fed electrospray thrusters are highly compact, including fully integrated propellant supplies, and are capable of ~100nN thrust precision with 10’s of nN noise. Thrust can be accurately throttled over >30x, up to a scalable maximum of 10’s to 100’s of uN. While typically operated in largely continuous states they are unique in that emission can be electrically stopped/started at ms time scales. Thus, extremely low impulse bits may be achieved over very short durations, permitting throttling from <0.1uNs up to 100’s of uNs. Realization of this fundamental capability of the technology is presently limited by control circuitry. The proposed work seeks to study and overcome these limitations with a new control methodology.These traits, combined with >800s specific impulse, and thereby low propellant mass could enable these systems to replace traditional reaction wheel ACS and high-propellant mass cold gas systems; enabling milliarcsec control authority for CubeSats versus the present arcsec level SOA.