Variable-Isp Ionic Liquid Electrospray Thruster

Busek proposes, with the MIT Space Propulsion Lab, to develop and characterize a variable-Isp colloid thruster operating only in the ionic mode and achieving its variable-Isp through use of a deceleration grid.  This approach overcomes the usual inefficiencies encountered in variable-Isp colloid thruster operation, where lower Isp is accomplished through operation in droplet or mixed droplet/ion modes.  An additional benefit is that the variable-Isp operation can be obtained under constant power.  For the Phase 1 effort, the Busek/MIT team shall develop a linear emitter using photolithographic mask transfer and electrochemical etching on porous tungsten substrates.  The emitter will subsequently be operated to determine V-I characteristics, verify ion emission and the decelerator concept, and perform time-of-flight measurements.  Following these tests, direct thrust measurements shall be performed on Buseks magnetically levitated thrust stand to obtain direct thrust and Isp measurements.  The linear emitter architecture will be designed in order to be suitable for multiplexing into thruster units able to provide greater thrust levels.  Subsequent Phase 2 work would be to multiplex emitters and develop a deliverable 1mN class thruster with variable Isp of 500-5000 seconds. 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 pure 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.)