Phase Four, a provider of next generation electric propulsion (EP) solutions for satellites, was awarded a $14.9-million contract by the Defense Advanced Research Projects Agency (DARPA) to deliver an air-breathing EP system to enable extended satellite operations in Very Low Earth Orbit (VLEO), at altitudes as low as 90-450 km.

Phase Four’s radio-frequency thruster under test at its facility in Hawthorne, CA.

The award is part of DARPA’s Otter program, which aims to develop, demonstrate, and collect on-orbit data for air breathing electric propulsion technologies that will harvest ambient low-density air as propellant, enabling extended satellite operations at VLEO altitudes. The Otter program will culminate in a long duration orbiting wind tunnel spaceflight demonstration, characterizing the performance of the air-breathing EP system in the orbital environment.

DARPA’s Otter program will leverage Phase Four’s innovative core technology, the radio frequency thruster (RFT), which is inherently propellant agnostic compared to legacy electric propulsion systems which rapidly degrade when exposed to non-traditional propellants. This feature uniquely enables the RFT to operate on the low-density air harvested in the VLEO environment. The Otter program will build upon a previous effort with DARPA that developed a proof-of-concept thruster prototype for novel, low-cost propellants.

Phase Four’s RF plasma thruster operates by using RF to heat propellant into ionized plasma that is then ejected away from a spacecraft by a permanent magnet, creating thrust. This simple design avoids high voltage electronics and eliminate components that are challenging to manufacture in large quantities, like the hollow cathode. These innovations allow Phase Four to achieve a 75% reduction in lead time and materials cost compared to leading Hall thrusters.

Phase Four 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 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.