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Phase Four

Compact electric propulsion for space

Broken up in 2025: the Hall-effect thruster line was sold to Apex, and the multi-mode propulsion tech plus the Hawthorne facility to Quantum Space. Phase Four operated in the propulsion sector of the space industry, was headquartered in United States, was founded in 2015, reached Series B stage.

Phase Four at a glance

StatusAcquiredchecked August 2026Broken up in 2025: the Hall-effect thruster line was sold to Apex, and the multi-mode propulsion tech plus the Hawthorne facility to Quantum Space.
SectorPropulsion
HeadquartersUnited States
Founded2015
StageSeries B
Team size11-50
Websitephasefour.io

Record last updated August 2026 · how we verify · spotted something outdated? Tell us.

We interviewed Umair Siddiqui

How Phase Four Is Simplifying Electric Propulsion To Propel The Space Economy

Read the interview

Mission

Its electrodeless radio-frequency plasma thruster scales from CubeSats up to bus-sized satellites.

Based in El Segundo, California, Phase Four is enabling the exponential growth of satellite constellations by solving the satellite’s costliest problem, the propulsion system. The company’s electrodeless RF thruster is the smallest plasma propulsion system available today, and can be scaled for use from CubeSat to SmallSat to school bus-sized satellites. By eliminating the most common failure points in incumbent technologies – electrodes, high-voltage electronics, and complex fabrication – Phase Four has built a system that is reliable and offers high-performance with baked-in manufacturability. Designed with tomorrow’s satellites and constellations in mind, the P4 RF thruster brings SmallSats the same performance levels of large satellites, in a simpler form factor.

Team

  • Simon Halpern · Founder
  • Steve Kiser · CEO

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