The Advanced Development team is working to adapt Phase Four’s flight heritage radiofrequency thruster (RFT) technology, part of the commercial Maxwell satellite propulsion system, to operate on the Air Force Research Laboratory (AFRL)-developed next generation green propellant, Advanced Spacecraft Energetic Non-Toxic (ASCENT). This adapted RFT will be the cornerstone for a multimode propulsion system which will allow future space vehicles the ability to operate at both high thrust (chemical monopropellant thruster) and high efficiency (the Phase Four RFT), using a single, common propellant. The result: a multimode system with reduced fluid storage and handling complexity and number of components in the space vehicle, thus increasing reliability, reducing mass, and enhancing maneuverability.

Phase Four’s RF plasma thruster is comprised of an inductive plasma source that operates at 10-100x greater volumetric power density compared to typical RF plasmas seen in the plasma processing industry. At Phase Four we have observed significant populations of very energetic non-thermal electron populations in the plasma plume. Furthermore we have evidence for very high ion temperatures in our system, both of which play a large role in generating thrust. State of art plasma models do not accurately convey these driving factors in our RF source.

To understand these phenomena better, with an eye to improving performance, we map plasma parameters and thrust as a function of every tunable parameter in the system. To optimize this process, we are building an automated thruster mapping system where we will take a new thruster design and automatically vary every tunable parameter while simultaneously measuring performance and plume characteristics. This will accelerate the optimization and performance improvements and generate very large sets of data to lead the development of advanced RF plasma thruster models.

UPCOMING PERFORMANCE IMPROVEMENTS IN THE RF THRUSTER

Phase Four has already performance tested the next RF plasma thruster to enter into the next Maxwell Block. This new thruster doubles the peak specific impulse compared to Block 1 and Block 2 to above 900 seconds, doubling total impulse for a fixed propellant tank size or reducing the wet mass and volume of the total propulsion system.