Colloidal microthruster plume diagnostic development

Degen, Brad; Pearce, Kevin

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Colloidal microthruster plume diagnostic development

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Colloid thrusters provide a thrust on the order of 10 micro-newtons, a single needle produces on the order of 1 uN which will allow for precise attitude control of spacecraft. With Micro-newtons of thrust, measurements using a thrust stand are very challenging. Due to the difficulty of conventional thrust measurements at such a low level, a TOF (Time-of-Flight) spectrometer can be used. From the TOF data, performance parameters of the colloid thruster plume, such as thrust, specific impulse, and mass flow rate can be calculated indirectly. This report describes the design, construction and initial testing of a micro-ammeter and a high voltage shutoff circuit for a TOF spectrometer, which will be used to test a colloidal thruster. Also an emitter priming circuit will be described that will prime the emitter through actuation of a valve allowing propellant to flow to the tip of the emitter. Upon completion of the project all components functioned as initially expected. The high voltage switch pulsed a 4000V source compared to the original design target of 3000 V. The electrometer converted a 1 nA input signal to a 1mV output signal once the offset was nulled. In addition, the electrometer was calibrated over the current range of interest and calibration factors are provided. Finally, the range of pulse widths for the priming circuit was determined to be between 128 us and 30.56 ms due to a slow rise time and a valve driving voltage of 5 V. Although different from the original estimates for pulse width, operation in this range met the reqauirements.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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