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Halo PPU

The PPU for Halo is designed to meet the needs of LEO spacecraft with flexible in-flight throttling, allowing changes to the operating point as needed. By varying the anode voltage between 150 to 300 V, mission planners can trade between thrust and specific impulse. This enables higher thrust early in the mission for faster orbit reach and higher specific impulse for stationkeeping to conserve propellant and extend mission lifetime.

The PPU communication interface options include RS422, RS485, or CAN serial types, and it accepts unregulated voltage from 22-36 V. The unit is rated to 30 kRad TID, with an upgrade option to 100 kRad TID. The PPU weighs 1.88 kg and fits within a 21 x 5 x 18 cm volume.

Halo 12 PPU

The PPU for Halo12 has been designed with flexibility to meet the needs of GEO spacecraft. The PPU can throttle in flight, providing the flexibility to change the operating point as the mission requires. For instance, varying the anode voltage between 200V to 600V allows mission planners to trade between thrust and specific impulse. This allows the satellite to operate at a higher thrust early in the mission to reach its operating orbit (and begin operations) faster. For station keeping the thruster voltage can be increased, providing higher specific impulse to conserve propellant and extend mission lifetime.

The PPU communication interface is a dual redundant, full duplex RS422 serial type. The unit accepts either 26-34V for our low voltage isolated PPU, or 85-150V for our high voltage isolated or un-isolated PPU. The cards are rated to 100krad TID, and mass and dimensions vary based on the PPU configuration selected for use.


Propellant Flow Controller (PFC)

Designed for CubeSats, the ExoTerra Propellant Flow Control (PFC) Module offers a wide throttle range with minimal size, weight, power, and cost. Initially developed for xenon, the PFC also works with lower-cost krypton propellant.

The PFC features a modern, simplified control architecture for independent control of anode, cathode, and startup flow lines. With an inlet pressure of 50 psia, the anode control line meters up to 5 mg/s of xenon in precise increments as small as 0.05 mg/s, and the cathode control line meters up to 0.8 mg/s for on-orbit adjustments. The startup control line can deliver up to 10 mg/s of xenon gas for igniting the Hall thruster hollow cathode. These flow rates cover the entire power range of ExoTerra's Halo and Halo12 thrusters.

The compact PFC unit fits within a 10 x 5.5 x 4 cm envelope, with additional propellant management components for tank pressure management up to 3,000 psia packaged within a total volume of less than 1U.



The Pressure Manifold Assembly (PMA) serves as the pressure isolation stage between a pressurized fueling tank and the Propellant Flow Controller (PFC). It enables the use of both xenon and krypton, allowing pressure control from 4500 psi down 20 psi while operating with either gas. Two pressure transducers are held within the manifold to read both the higher upstream pressure, usually used as a fuel tank readout, and the lower downstream pressure to verify the inlet control to the PFC. In between the pressure transducers lies a latching valve to ensure isolation between the high-pressure and low-pressure sides of the feed system, as well as a pressure regulator for the pressure control. The PMA also includes a thermistor as well as a controllable heater to keep the system within operational temperatures. One PMA has the capacity to supply enough flow to dual-string Halo and Halo 12 systems including the ignition of the thrusters. 

The PMA provides tube stubs on the inlet and the outlet of the manifold to offer flexible interfacing into the feed system. In total, the mass of the PMA sits at 575 grams held within a volume of 116.8 cubic centimeters. The equipment included in the PMA is all interfaced to and controlled by ExoTerra's PPU’s for both Halo and Halo 12 systems.

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