Lifetime Trend Testing of the Phase Four RF Thruster for Small Spacecraft Missions (RF Thruster)

This partnership aims to perform lifetime trend testing of the Phase Four Radio Frequency Thruster (RFT) utilizing vacuum chambers and subject matter expertise resident at NASA Glenn Research Center (GRC). Results will allow for a lifetime estimation of the thruster and determine possible failure modes.

Phase Four has developed the RFT as a novel approach to electric propulsion for small spacecraft. RFTs are electric propulsion systems that use radio frequency electromagnetic signals to accelerate a plasma propellant, generating thrust. Phase Four’s RFT is an electrothermal RF thruster that drives ion acceleration primarily through heating of constituent plasma particles via the applied RF signal. An antenna transmits RF energy into a magnetic nozzle, creating a plasma. A electrons are then accelerated out of the nozzle, and the resulting charge imbalance pushes ions into the same direction, creating an ambipolar flux of particles. The ion acceleration is the primary source of thrust. Competing approaches use electromagnetic forces to accelerate ions. The electrothermal approach simplifies the design.

This project is a collaboration between Phase Four and (GRC) and was originally meant to support future long duration missions for small spacecraft by collaborating with Phase Four to perform lifetime trend testing on the RFT. This testing encompassed 1,000 hours of thruster operation time with appropriate diagnostics to determine the degradation rates and failure modes of the thruster. Before the 2020 Announcement of Collaboration Opportunity (ACO) was awarded, Phase Four had limited data on the RFT. With the objectives of the 2020 ACO completed, Phase Four will be able to better predict the actual life of the RFT and the impact that lifetime would have on its small spacecraft customer base.

The partnership resulted in various tests running several hundreds of hours, leading to improvements in the technology.

Phase Four’s (RFT) delivers plasma propulsion performance while eliminating high-cost, complex components found in legacy electric propulsion systems such as hollow cathodes and high voltage electronics. Traditionally, Hall Effect thrusters use life-limiting hollow cathodes as plume neutralizers or gridded ion engines with high voltage grids in addition to neutralizing cathodes. Hollow cathodes, in particular, are highly sensitive to contamination and must be run with expensive, inert gases such as xenon or krypton. The ambipolar nature of Phase Four’s RFT has eliminated the need for a neutralizer, while producing thrust and specific impulse levels required for small spacecraft operations. Additionally, through the use of RF rather than high voltage for the acceleration mechanism, the power processing unit that supports the RFT is vastly simplified, achieving lower mass and volume as well.

Potential end-users include operators of small spacecraft equipped with propulsion systems. This technology could increase the cost-effectiveness of these systems.

This is a mature technology (TRL 8) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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