Lower Limits of Performance of an Electrospray Thruster using a Direct Measurement Method

Nanosatellites are a growing technology that offer a more accessible way for scientific missions to be conducted in space. The number of nanosatellites launched annually continues to grow, increasing the need for a propulsion system onboard to assist in collision avoidance, station keeping, rendezvous, and other attitude adjustments. More importantly though, new rulings have dictated that all orbiting spacecraft must deorbit within five years of mission completion to help mitigate the evergrowing problem of space debris. Electrospray thrusters, a subset of electric propulsion, is a well-researched method of propulsion for nanosatellites, including the novel µSTAMPS thruster currently in development at the University of Tennessee Space Institute (UTSI). Among the characteristics of these types of thrusters are high specific impulse with low thrust, and therefore, low thrust to weight ratios. Performance characterization is imperative to ensure a given mission can be completed without adding any more mass from propellant than is required. Traditionally, thrust stands are based on a torsional balance, hanging pendulum, or inverted pendulum approach, all of which required extensive and complex calibration and damping systems to resolve the forces expected from electrospray thrusters. The objective of this work is to determine the lowest level of thrust that can be measured by a simpler direct measurement technique involving the use of a weigh cell. This work focuses on the experimental set-up to baseline the selected weigh cell and determine the lowest level of thrust that is accurately measurable. The lowest thrust level measured was an impressive 1 µN. The µSTAMPS is anticipated to produce measurable force under viits current design. This work will then go on to make recommendations for future improvements.