Staging of electric propulsion systems: Enabling an interplanetary Cubesat

Advances in miniaturization using micromachining processes have led to propulsion systems small enough to consider the feasibility of carrying a large number of thrusters even on small spacecrafts such as Cubesats. Electrospray thrusters developed at the Space Propulsion Laboratory of the Massachusetts Institute of Technology are composed of a highly miniaturized emitter array attached to a tank structure. In terms of volume and mass, the thrusters are small compared to the tank and overall system. This feature makes it possible to envision a staging concept, in which multiple propulsion units are powered in succession, with staging of those that have depleted their propellant. As the satellite mission advances, such a staging operation reduces the spacecraft structural mass, leading to an increased total Dv capability compared to traditional mission designs. This work examines the impact of such an operational concept in the context of a Cubesat that is capable of raising its orbit from a geosynchronous orbit (GEO) to interplanetary space. While this concept can be applicable to missions of different interplanetary objects such as Near-earth-objects, a mission from GEO to lunar space is investigated in this work as an example. To fully assess the benefit of the staging concept, comparison to a more traditional mission approach is made. When comparing the staging method to a fixed structural spacecraft for a 3U Cubesat, the reduction of propellant mass and time of flight is 12.7% for a transfer from GEO to the Moon's Sphere of Influence.