Phase Four

Phase Four is a specialist aerospace propulsion provider based in the United States, operating as a Tier 2 or Tier 3 supplier within the small satellite value chain. The company focuses on the development of electric propulsion systems that utilise radio frequency plasma technology. Their hardware is designed to provide in-space mobility for CubeSats and larger small-satellite constellations, offering an alternative to traditional chemical thrusters or legacy Hall-effect systems by simplifying the internal architecture and eliminating high-voltage electrodes. The organisation’s primary product line is the Maxwell engine, an integrated propulsion system that has achieved flight heritage on several commercial and government missions. They serve satellite bus manufacturers and constellation operators, including contracts with the U.S. Space Force and the Air Force Research Laboratory. The company maintains partnerships with launch providers and integrators to ensure their thrusters are compatible with standard satellite architectures and propellant varieties, including noble gases and iodine. Prospective partners should verify the specific impulse and thrust-to-power ratios relevant to their mission profile, as RF plasma performance varies significantly depending on the selected propellant. Buyers should also confirm the current lead times for flight-qualified units and ensure that the thermal management requirements of the thruster align with their satellite's power subsystem. Verification of previous on-orbit duty cycles is recommended to assess long-term cathode-less reliability.