Phase Four's Second Generation RF Thruster, Maxwell Block 2, firing in one of the company's vacuum chambers. Credit: Phase Four

SAN FRANCISCO — Propulsion startup Phase Four has signed a memorandum of understanding with satellite refueling startup Orbit Fab aimed at preparing future Phase Four Maxwell engines for on-orbit refueling.

“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 said in a statement. Working with Orbit Fab “is an obvious step” for Phase Four to ensure “future customers have the option to refuel their spacecraft and extend mission lifetime,” Jarvis added.

Under the agreement announced Jan. 24, the companies will work together to evaluate the refueling potential of traditional electric propulsion propellants like xenon for Phase Four Maxwell engines as well as new propellants like Advanced Spacecraft Energetic Non-Toxic propellant or ASCENT, a monopropellant developed by the Air Force Research Laboratory.

“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,” Jarvis said.

In December, Phase Four unveiled its second-generation of satellite thrusters that rely on radio frequency technology to produce plasma. The El Segundo, California, startup plans to begin delivering the new thrusters to customers later this year.

Orbit Fab has developed an interface for spacecraft refueling called Rapidly Attachable Fluid Transfer Interface or RAFTI. The Denver-based startup sent its first fuel depot, Tanker-001 Tenzing, into low Earth orbit last year.

For Phase Four, “collaborating with a talented Orbit Fab team will enable extended mission lifetimes, which unlock a variety of mission applications in LEO and beyond,” Bryce Dabbs, Phase Four vice president, told SpaceNews. “This is particularly important for our team and customer base as, although we’ve proven flight operability utilizing traditional propellants like xenon, our fuel-agnostic engines are expanding their aperture to more advanced propellants which significantly enhance performance parameters of interest for dual-use applications.”

For a long time, there was something of a chicken-and-egg problem with in-orbit refueling. Spacecraft were not designed to be refueled because no orbital refueling options existed. That is beginning to change.

“The causality dilemma between in-orbit refueling services and engines designed to be refueled tips heavily in our team’s favor,” Dabbs said. “Our engines are designed to offer simple plug-and-play capability in customer spacecraft. We also strive to be forward-looking in terms of future capabilities that customers may request.”

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...