Exploration of Planetary Bodies with Electrospray Thrusters

Abstract

The exploration of planetary bodies such as asteroids can provide insight into the development of the solar system and targets for future in situ resource utilization. However, the current paradigm of using a single, monolithic, spacecraft limits the number of asteroid visits to one every few years. By using fleets of standardized small spacecraft, the frequency of asteroid visits could be dramatically increased while simultaneously decreasing the cost per visit. With the development of miniaturized spacecraft systems beginning to mature, attention also needs to be given to methodologies for operating these small spacecraft.

Electrospray propulsion is a promising technology for high-Delta-v propulsion of small spacecraft due to its mechanical simplicity and scalability. However, methodologies for characterizing the propulsion system thrust on orbit have so far been underdeveloped, and are required for continued development of electrospray thrusters. In addition, the use of electrospray thrusters during operations around or on an asteroid can have further implications. First, the low thrust density of electrospray propulsion, relative to monopropellant or cold-gas propulsion, likely constrains many propulsion architectures to have a single thrust axis with respect to the spacecraft body, complicating the trajectory design process. Second, the ability to operate electrospray thrusters in a bipolar configuration opens up new mission possibilities that leverage intentional charging of the parent vehicle as well as the surface of the planetary body in order to create electric forces for actuation.

This thesis resolves three technical challenges associated with the application of electrospray thrusters for potential planetary exploration missions. Numerical and analytical approaches for inferring the thrust output of a propulsion system based on a simple orbital maneuver are developed. These approaches allow for characterization of the propulsion system performance including quantification in the uncertainty of the thrust output. The controllability of an underactuated spacecraft during proximity operations is also resolved, and an analytical maneuver library is derived in order to guide the spacecraft through different maneuvers. Finally, the application of electric forces for a novel form of actuation on the surfaces of atmosphere-less planetary bodies is analyzed in order to enable a small vehicle to anchor the surface of a rotating asteroid or potentially achieve levitation.