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Phase Four and OrbitFab to Collaborate on in-Orbit Refueling

By Doug Messier
Parabolic Arc
January 25, 2022
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Companies seek to explore collaboration with RAFTI™ refueling system and Maxwell engines using both traditional and advanced propellants

EL SEGUNDO, Calif., January 24, 2022 (Phase Four PR) –– Phase Four, the creator of the radio-frequency thruster for satellite propulsion, announced today that it has signed a memorandum of understanding with Orbit Fab, the market leader for in-orbit refueling services and the creator of RAFTI, the industry standard satellite refueling interface. The companies seek to ensure that future Phase Four Maxwell engines may be refueled in-orbit to extend mission lifetimes and maximize ROI for spacecraft. The companies will evaluate RAFTI compatibility for refueling of traditional electric propulsion propellants such as xenon as well as advanced propellants such as ASCENT available to Phase Four’s propellant-agnostic core technology – the RF Thruster.

“As we build and deliver an increasing number of Maxwell engines to customers, we want to be forward-looking for mission lifetime extension services such as in-orbit refueling,” said Phase  Four CEO, Beau Jarvis. “Orbit Fab is the leader in developing a docking and refueling-capable interface in the form of RAFTI. For this reason, working together is an obvious step for us in making sure future customers have the option to refuel their spacecraft and extend mission lifetime.  Additionally, we are excited by the prospect of investigating refueling with non-traditional propellants that are significantly less expensive or more densely storable than traditional noble gases like xenon.”

Phase Four delivered its 10th Maxwell Block 1 engine in December 2021 and engines are currently operating on several commercial small satellites, including two Maxwell engines recently launched on the SpaceX Transporter 3 rideshare of January 12, 2022.  The company has also demonstrated industry leading production and delivery times of under four months through consecutive production runs. The Maxwell Block 2 engine, which incorporates the 2nd generation RF Thruster and new high performance electronics is set to enter production in the first quarter of 2022.  This engine offers more flexibility to customers and addresses a larger segment of the high growth small satellite industry. 

“With the advent of in-orbit refueling services being developed by Orbit Fab, our goal is to ensure propulsion systems like the Phase Four Maxwell engine are capable of being refueled via our hardware and services” said Orbit Fab CEO, Daniel Faber. “We are encouraged by the electrodeless design of Phase Four’s technology, which has promise for significantly longer lifetimes and reduced degradation. Having future versions of the Maxwell engine compatible with RAFTI will enable spacecraft operators to significantly extend mission lifetimes and add additional ROI for these assets in space.” 

The RAFTI fueling port was first demonstrated on Orbit Fab’s Tanker-001 Tenzing propellant depot, which launched to low Earth orbit in June 2021. Orbit Fab seeks to make in-orbit refueling accessible to all satellite operators through working with channel partners like Phase Four and through initiatives such as the recent release of the RAFTI™ Open License.

About Phase Four

Phase Four is a disruptive provider of next generation electric propulsion (EP) solutions for small satellites. The company 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 revolutionary 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. Learn more at

About Orbit Fab

Orbit Fab is building a bustling in-space economy, beginning with a propellant supply chain. The company’s Gas Stations in Space™ services create a bridge between Earth and space, providing satellite owners with the necessary propellant to extend mission time, travel across orbits, and even return to Earth. World-firsts include the first commercially available satellite refueling port RAFTI, the first in-orbit fuel depot, and the first resupply of water to the International Space Station by a private company. Orbit Fab is backed by key industry leaders and major investors including Lockheed Martin, Northrop Grumman, SpaceFund, Bolt, Munich Re Ventures, and more. The company recently announced its first commercial fuel sale to Astroscale, a private orbital debris removal company headquartered in Tokyo, Japan. Visit for more information.      

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