Stage-Based Electrospray Propulsion System for Deep-Space Exploration with CubeSats

Abstract

Independent deep-space CubeSat missions require efficient propulsion systems capable of delivering several km/s of ∆V. The ion Electrospray Propulsion System under development at MIT's Space Propulsion Laboratory is a high ∆V propulsion system that is a promising technology for propulsion of independent deep-space CubeSat missions due to its mechanical simplicity and small form factor. However, current electrospray thrusters have demonstrated lifetimes up to an order of magnitude lower than the required firing time for a mission to a near-Earth asteroid starting from geostationary orbit. A stage-based concept is proposed where the propulsion system consists of a series of electrospray thruster arrays. When a set of thrusters reaches its lifetime limit, it is ejected from the spacecraft exposing new thrusters thereby increasing the overall lifetime of the propulsion system. Such a staging strategy is usually not practical for in-space thrusters. However, the compactness of micro-fabricated electrospray thrusters means that their contribution to the overall spacecraft mass and volume is small relative to other subsystems. Mechanisms required for this stage-based approach are proposed and demonstrated in a vacuum environment. In addition, missions to several near-Earth asteroids with orbital elements similar to those of Earth are analyzed with a particular focus on the escape trajectory. With a stage-based approach, independent deep-space CubeSat missions become feasible from a propulsion standpoint.

Development and Laboratory Testing of a CubeSat-Compatible Staged Ionic-Liquid Electrospray Propulsion System

“…The hold-down and release mechanism concept selection was previously studied [17] and demonstrated in a vacuum environment [14]. A simplified miniature fuse wire release mechanism [18] was selected because of its compactness and high load carrying capacity, while avoiding potentially hazardous technologies such as pyrotechnics.…”

“…The second generation of this concept was developed in STEP-1 to conform with the CubeSat standard and further optimise the design. The first generation design [17] nested the fuse wire and separation springs inside a ceramic standoff in each corner of the stages. Since this limited the load-carrying capacity of the stages and required relatively large board spacing the fuse wire was moved to an adjacent wire block on the circuit board and the ceramic interface was replaced with conical mating features directly integrated into the metallic structure of the stage, shown in Fig.…”

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

“…This allows the same power processing unit to be used for a staged configuration as well as a traditional single array configuration. Further information on the staging and routing mechanisms can be found in [11] and [14]. This configuration, while designed for a 3U CubeSat, is easily scalable to large form factors.…”

“…Current electrospray thrusters have lifetimes of around 500 hours, which is insufficient to perform such a mission. Even if trajectories which attempt to minimize the required firing time are devised or if expected near-term advancements in electrospray thruster performance are met, the firing time of an individual thruster will be lower than the required firing time for escape [11].…”

“…Staging of electrospray thrusters was originally analyzed in [13] to explore reductions in the transfer time of a lunar mission. Preliminary design and analysis on the required mechanisms for a stage-based approach are investigated in [11] along with analysis of the use of staging for missions to several near-Earth asteroids. Most recently, a laboratory demonstration of staging with electrospray thrusters was conducted in [14] which demonstrated the mechanical and electrical feasibility of such a configuration.…”