Phase Four
Developed electrodeless radio-frequency and multi-mode electric propulsion systems for satellites
Phase Four was an aerospace company that designed and manufactured electric propulsion systems for satellites. Founded in 2015 in Hawthorne, California, the company developed radio-frequency (RF) thruster technology that eliminated electrodes, high-voltage electronics, and complex fabrication processes found in conventional Hall Effect and ion engines. Its flagship Maxwell engine used an electrodeless RF plasma design that was propellant-agnostic, enabling operation on traditional and alternative propellants including ambient atmospheric gases.
Phase Four delivered 13 flight units to orbit and held eight government contracts, including a $15 million DARPA contract under the Otter program to develop air-breathing electric propulsion for very low Earth orbit operations. The company also developed multi-mode propulsion systems capable of operating in both chemical and electric modes.
In September 2025, Phase Four's assets were divided between two acquirers: Apex acquired the Hall Effect thruster technology and personnel, while Quantum Space acquired the multi-mode propulsion assets and the Hawthorne integration and test facility.
Designs electric propulsion systems for small satellites and operates orbital transfer vehicles for last-mile delivery and in-orbit services
Designs and manufactures Hall-effect plasma propulsion systems for small satellites, with AS9100D-certified high-volume production
Designs and manufactures chemical, electric, and hybrid propulsion systems for spacecraft ranging from cubesats to orbital transfer vehicles