Variable-Isp Ionic Liquid Electrospray Thruster

ABSTRACT: Busek proposes, with the MIT Space Propulsion Lab, to leverage successful Phase I proof-of-concept results to develop and deliver a 1mN, micro-fabricated electrospray thruster that features variable Isp and bi-polar operation. The thruster achieves variable Isp at no power penalty by innovative use of a deceleration grid, and operating in purely ionic mode so as to overcome many of the grid-contamination life-limiting issues that impeded true MEMS development in the past. Applying this novel deceleration grid concept solves the problem of obtaining lower ISP during ionic operation. The development effort shall focus upon optimizing thruster emitter and grid geometries in order to ameliorate grid interception problems encountered in the Phase I. Once suitable geometries have been established, a true MEMS thruster shall be fabricated and characterized. Supporting the testing effort shall be development of an integrated bipolar switching PPU/DCIU in order to enable direct thrust measurements on Busek"s magnetically-levitated thrust stand. At the conclusion of the Phase II program, Busek and MIT shall deliver a 1mN prototype micro-fabricated thruster, powered by a bipolar switching PPU/DCIU and capable of an Isp range of 500 to 5000s. BENEFIT: Features of the proposed effort are: a colloid thruster able to operate only in ionic mode; variable Isp operation spanning 500-5000 seconds; and constant power operation. The benefit of purely ionic operation is that it avoids the inefficiencies of mixed-mode (droplet + ion) operation. Variable Isp provides versatility in a single thruster system, allowing for operations such as highly mass-efficient station-keeping as well as rapid maneuver that would otherwise require multiple systems. Constant power operation allows for simplification of power electronics design as well as reduced demands on the spacecraft bus, where variable power thrusters complicate power allocation and margin requirements. The concept promises to enable true MEMS fabrication of a practical colloid thruster, a goal that to date has been elusive due to challenges in obtaining low-Isp operation without debilitating thruster grid contamination