Feasibility of a Deep-Space CubeSat Mission with a Stage-Based Electrospray Propulsion System

Independent deep-space exploration with CubeSats, where the spacecraft independently propels itself from Earth orbit to deep-space, is currently not possible due to the lack of high- $\Delta\mathrm{V}$ propulsion systems compatible with the small form factor. The ion Electrospray Propulsion System (iEPS) under development at the Massachusetts Institute of Technology's Space Propulsion Laboratory is a promising technology due to its inherently small size and high efficiency. However, current electrospray thrusters have demonstrated lifetimes (500 hours) below the required firing time for an electrospray-thruster-propelled CubeSat to escape from Earth starting from geostationary orbit (8000 hours). To bypass this lifetime limitation, a stage-based approach, analogous to launch vehicle staging, is proposed where the propulsion system consists of a series of electrospray thruster arrays and fuel tanks. As each array reaches its lifetime limit, the thrusters and fuel tanks are ejected from the spacecraft exposing a new array to continue the mission. This work addresses the technical feasibility of a spacecraft with a stage-based electrospray propulsion system for a mission from geostationary orbit to near-Earth asteroid 2010 UE51 through a NASA Jet Propulsion Laboratory Team Xc concurrent design center study. Specific goals of the study were to analyze availability of CubeSat power systems that could support the propulsion system and any other avionics as well as requirements for attitude control and communication between the spacecraft and Earth. Two bounding cases, each defined by the maturity of the iEPS thrusters, were considered. The first case used the current demonstrated performance metrics of iEPS on a 12U CubeSat bus while the second case considered expected near-term increases in iEPS performance metrics on a 6U CubeSat bus. A high-level overview of the main subsystems of the CubeSat design options is presented, with a particular focus on the propulsion, power, attitude control, and communication systems, as they are the primary drivers for enabling the stage-based iEPS CubeSat architecture.