High Specific-Impulse Electrospray Explorer Trajectory Guidance and Control Air Bearing Demonstration

As small satellite-mission concepts that require travel farther from their traditional domain of low-Earth orbit are being considered, there is a growing need to develop small-scale propulsion systems that can provide the necessary net impulse to enable deep-space operation. The High Specific-Impulse Electrospray Explorer for Deep-Space (HiSPEED) project is an example concept considered for this paper, as it would be a small satellite that uses electrospray thrusters to navigate along a low-thrust spiral trajectory from Earth to a near-Earth asteroid. The NASA Jet Propulsion Laboratory Small Satellite Dynamics Testbed operates simulation and air- bearing testing environments. This paper focuses on its planar air-bearing platform used to create a nearly frictionless environment in three degrees of freedom: two translational and one rotational. The platform maneuvers using eight compressed air thrusters controlled by an onboard single-board computer using position feedback from a motion-capture system. This paper discusses the design, development, and testing of a closed-loop controller for this platform that enables trajectory following with position error less than 4 cm. The paper presents data from tests representative of HiSPEED spiral escape trajectories and operations in proximity to an asteroid, along with implications for HiSPEED and similar concepts.