Development and Characterization of the Capacitive Power Processing Unit (CPPU) for the Micro-Cathode Arc Thruster
Open AccessBecause of their inherently strict mass, volume, and power consumption limitations, to date relatively few CubeSats have flown with propulsion systems onboard. Micro-cathode arc thrusters (μCAT), a subset of vacuum arc thrusters (VAT) that have flown successfully on BRICSat-P and CANYVAL-X, have traditionally used inductive energy storage (IES) power processing units (PPU) to convert a CubeSat’s onboard power to the levels required for μCAT operation. Although individual IES PPU mass and volume are rather low, propulsion system total mass and volume can become prohibitively large for smaller CubeSats when missions require multiple μCATs, as each μCAT requires its own IES PPU in order to operate. The capacitive power processing unit (CPPU) employs inductor-capacitor energy transfer to increase integrability of propulsion systems utilizing multiple μCATs in CubeSats, without greatly sacrificing propulsion system functionality and performance. In this thesis, a comparison of the IES PPU and CPPU is presented. Transient analysis of circuit operation and PPU performance over a common discharge energy range, which corresponds to a total propulsion system power consumption of 6 - 8 W, are explored through a series of experiments. Energy efficiencies of up to 94% and up to 76% were achieved using the IES PPU and CPPU respectively, depending on desired discharge energy levels and PPU charging schemes. Ion current measurements indicated that the IES PPU was roughly 1.5× to 1.9× more efficient than the CPPU at utilizing μCAT propellant. Although thrust measurements showed that the IES PPU could achieve a thrust to power ratio roughly 1.5× to 4.3× that of the CPPU, the CPPU was able to produce thrust within the range of the IES PPU and was found to reduce the total propulsion system mass and volume by up to 77% and 68% respectively.
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