Space Commerce

Phase Four Achieves Electric Thruster Operation on Air Force Green Propellant ASCENT

By Keith Cowing
Press Release
Phase Four
November 11, 2022
Filed under ,
Phase Four Achieves Electric Thruster Operation on Air Force Green Propellant ASCENT
Phase Four, a best in class provider of electric radio frequency (RF) thrusters for in-space propulsion
Phase Four

Phase Four, the creator of the radio-frequency thruster (RF thruster) for satellite propulsion, announced today that it has successfully demonstrated operation of its RF thruster using the Air Force Research Laboratory’s green propellant, ASCENT (formerly AF-M315E).

The achievement, made under a U.S. Space Force contract awarded at the 2021 Space Force Pitch Day, enables multi-mode propulsion capability, which combines the high thrust capabilities of liquid chemical propulsion with the high efficiency capabilities of electric propulsion operating on a single common propellant.

Phase Four’s RF Thruster to enable new ‘multi-mode’ propulsion capabilities for national security missions

“This achievement further underlines the expansive capability of Phase Four’s propulsive technology, which has already been shown to operate on other novel propellants such as iodine and water. We are proud to work alongside AFRL to now demonstrate RF thruster operation on ASCENT and build upon the versatility of this green propellant,” said Jason Wallace, Vice President of Advanced Development at Phase Four.

Jim Bridenstine, former NASA Administrator and recent addition to the Phase Four board of directors, added “With the increasingly congested and contested space domain, ASCENT-based RF thrusters are a critical technology to ensure the United States’ propulsive superiority in space.”

Phase Four tested the RF thruster while flowing ASCENT and the individual gases that make up the green propellant. Throughout the test, Phase Four demonstrated ignition and stable firing over a wide spectrum of thruster operating points, achieving the world’s first cathode-less ASCENT plasma. Future development will focus on fine-tuning plasma performance for ASCENT and other liquid propellants used in monopropellant and bipropellant thrusters, with a focus to provide future space vehicles with the ability to maneuver without regret by delivering operational, turn-key multi-mode propulsion systems.

“Before joining Phase Four, I had the privilege of working with U.S. Space Force senior leaders to build out the concept of multi-mode propulsion and outline the capability it could unlock for national security missions. It became apparent that a game-changing propulsion technology would be required. Only the Phase Four RF thruster provided the necessary architecture to achieve multi-mode capability using novel liquid propellants, such as ASCENT,” said Jesse Sidhu, Phase Four senior systems engineer and technical lead on the program. “I’m proud to say that the Phase Four team has brought what used to be science fiction into reality. We now look forward to optimizing our thruster and building on this program to deliver unprecedented mission-centric propulsive capability to our warfighters.”

About Phase Four

Phase Four is a disruptive provider of next generation electric propulsion (EP) solutions for small satellites. The company was founded in 2015 to address the demands of the rapid proliferation of satellite constellations and to accelerate the advancement of its radio-frequency thruster (RFT). The Phase Four RFT represents a revolutionary new architecture that realizes lower cost, mass-manufacturability, miniaturized power electronics, and propellant agnosticism over incumbent technologies, without compromising performance. In 2021 Phase Four’s Maxwell turn-key propulsion system achieved flight heritage and is now being regularly utilized by small satellite operators. Learn more at

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.