The design of the CubeSat required precision pointing of the thrust vector through the spacecraft center of gravity to minimize fuel usage for attitude correction. Because the center of gravity shifts over the course of the mission, a means of adjusting the thrust vector was needed. Existing space-qualified actuators were either too large, lacked the precision required for pointing, or could not handle the high temperature of the thruster.
The peizoelectric Hall effect thruster actuator provides a CubeSat-class actuator for precision thruster pointing. The thruster is mounted to a ball joint at the center of the thruster. A pair of piezoelectric actuators is attached at angles to the thruster. The piezoelectric actuators use electrical signals to move the actuators linearly in steps of just 20 runs. This tips the thruster in the required direction to aim the thruster through the center of gravity (c.g.). Feedback from the star camera informs the spacecraft of any change in attitude based on the adjustment. This information is used to correct pointing until the c.g. is located.
The piezoelectric actuators offer several advantages. First, the small step size allows for pointing accuracy to <l° with a 10° total swing. Second, the small size of the actuator allows it to be packaged with the small volume afforded by a 6U CubeSat. The piezoelectric requires no holding power, so after the adjustment is made, no further power is needed to keep it in place. Finally, the piezoelectrics can operate at up to 50 °C, and hold position at up to 70 °C, allowing them to be used with the high-temperature Hall effect thruster.
The innovation associated with this project is an integrated 6U CubeSat spacecraft design that reaches lunar orbit through the use of a highly mass-efficient solar array design, direct-drive solar electric propulsion, low-pressure iodine propellant, and a low-mass, low-cost, low-volume Hall effect thruster.
The significance of this innovation is that it offers affordable, high-output-power generation for small spacecraft, greatly expanding the range of CubeSat-scale missions and commercial applications. It scales SEP main propulsion to small spacecraft, enabling longer-duration missions and missions to a wider range of destinations. It uses a safe, solid-storable propellant, and fits within a standardized form factor in compliance with rideshare requirements, thereby keeping launch costs low. The integrated design serves as an affordable bus on which to build highly capable 12U CubeSats, allowing potential users to focus on their payloads rather than designing an entire spacecraft.