Phase Four

Phase Four operates in the aerospace and defense sector, focusing on the design and manufacture of advanced in-space propulsion systems for satellites. The company was established in 2015 by Simon Halpern and J. Sheehan to address the growing demand from the proliferation of satellite constellations. Halpern, the CEO, and Sheehan, the Lead Physicist, founded the company, which also received an early $1 million grant from DARPA.

The firm's business model centers on providing propulsion hardware, software, and services to commercial and government clients, including satellite operators and bus manufacturers. Phase Four aims to solve the high cost and reliability issues associated with traditional satellite propulsion by developing electrodeless radio-frequency (RF) thrusters. This technology eliminates common failure points like cathodes and high-voltage electronics found in legacy Hall thrusters, which were originally developed in the 1950s. The company has raised a total of $43.6 million over six funding rounds, with its most recent Series C round in January 2025 raising $12.9 million, led by Artemis Group Capital. These funds are allocated to scale manufacturing, accelerate R&D, and strengthen strategic partnerships.

Phase Four's product line includes the Maxwell and Valkyrie families of thrusters. The core technology is the RF Thruster (RFT), which uses radio-frequency energy to create and accelerate plasma for thrust, and is designed to be propellant-agnostic. This allows for the use of more accessible and less expensive propellants like iodine, nitrogen, and water, in addition to traditional options such as xenon and krypton. The Maxwell Block 1 engine achieved flight heritage in 2021 and is operational on several commercial small satellites. The subsequent Maxwell Block 2 and Block 3 engines offer significant performance enhancements. The company is also partnered with Redwire Space on the Valkyrie propulsion system, a Hall-Effect Thruster based on a NASA-licensed design, intended for missions from Low Earth Orbit (LEO) to cis-lunar space.

Keywords: in-space propulsion, satellite propulsion systems, electric propulsion, radio-frequency thruster, RF thruster, plasma propulsion, Hall-Effect Thruster, small satellites, satellite constellations, aerospace manufacturing, defense technology, propellant agnostic, iodine propellant, space mobility, satellite components, space technology, NewSpace, commercial space, government contracts, LEO