Station-keeping with an electrospray propulsion system for low lunar polar mission on a 6U cubesat

The suitability of electrospray propulsion for station keeping of a 6U CubeSat in lunar orbit is assessed. Lunar CubeSat missions are of interest with the launch of several CubeSat on-board the first Space Launch System launch. For interplanetary CubeSat missions, electrospray thrusters have the potential to provide good performance within the nanosat constraints. An electrospray thruster electrostatically accelerates charged droplets or ions, producing small thrusts at high specific impulse. To investigate the feasibility of using an electrospray system for station keeping, the maximum variation of orbital parameters for lunar polar orbits are evaluated. This was completed with the High Fidelity Orbit Dynamics (HiFiODyn), developed at Politecnico di Milano for orbit long-term propagation. The Gauss-planetary equations were integrated over time considering a 100 x 100 Lunar Prospector 165 x 165 spherical harmonic solution (LP165P) gravity model of the Moon and both the Earth and the Sun considered as third body. Without any propulsion system over a period of 70 days typical variations of orbital elements for low quasi-circular lunar polar orbits were assessed. Moreover, the evolution of different orbits was evaluated, with varying eccentricity and inclination and fixed initial epoch, semi-major axis, argument of perigee, longitude of the ascending node and mean anomaly. Maps of the maximum variation of all the Keplerian elements for these orbits were created. These maps have eccentricity that varies between 0.01 and 0.045 and inclinations that span from 85 to 95 degrees. A micro-electrospray propulsion system being developed at the University of Southampton was then considered in the simulation to assess its ability to keep a stable orbit. Both power and mass/volume were constrained for a 6U CubeSat using a model of a micro-electrospray thruster that allows an estimate of the thrust and the specific impulse. With thrust values of between 0.3 mN and 1 mN and specific impulse value of between 1000 s and 4000 s some different manoeuvres were performed to assess the ability of the propulsion system to maintain a prefixed value of an orbital parameter. The same maps were created with and without the electrospray propulsion system considered. It is demonstrated that the micro-electrospray system makes a significant difference to the variation with time of the polar orbit when a proper manoeuvre is used considering also that the thrust value of such system is much lower than typical perturbations of these low polar orbits.