Phase Four reports progress on cubesat thruster design

By Tom Risen|July 11, 2018

AIAA PROPULSION AND ENERGY FORUM, Cincinnati — The California-based satellite propulsion startup Phase Four targeting the emerging market for constellations of cubesats and small satellites unveiled test results of its electric radio frequency thrusters that exponentially outperformed a previous iteration tested earlier this year.

Phase Four released a report on Wednesday titled “Updated Performance Measurements and Analysis of the Phase Four RF Thruster” summarizing results of test firing of two thrusters tested in a vacuum chamber at Phase Four, one designed for a cubesat and another for a small satellite. NASA has classified small satellites as spacecraft smaller than 180 kilograms.

The report, written by Umair Siddiqui, chief scientist at Phase Four, cites a thrust output of up to 10 millinewtons, measures fuel efficiency at a specific impulse of up to 1500 seconds, and a thrust efficiency of 10 percent with a 1 percent margin of error for the tests conducted in April and May. These results mark exponential increases in performance from previous tests of the thrusters conducted by the U.S. Air Force-funded nonprofit Aerospace Corp. earlier in 2018, which in April reported generating 1.5 millinewtons of thrust at 300 seconds specific impulse.

Phase Four founder and CEO Simon Halpern told me prior to the AIAA Propulsion and Energy Forum that the thrusters went through four iterations of design changes between the start of April and the end of May with changes made after each round of testing. The latest results “get us on the playing field,” Halpern said, confident his firm can compete with other propulsion providers to sell thrusters for cubesats and small satellites to move where they need to go in space and to safely de-orbit at the end of their missions. Halpern founded the venture capital-funded company, which now has 20 employees, in 2015, the same year the company won a $1 million DARPA contract to build a prototype.

Satellites flying with Phase Four propulsion would supply electricity from solar panels to the thrusters that would power a magnetic field with radio waves to ionize xenon and force the heated plasma out of a nozzle to produce thrust.

Phase Four thrusters do not include an electrode to accelerate propellant, unlike some other forms of electric propulsion. Halpern says this means they can be mass produced at lower cost for newer constellations of satellites that are too small to be a good fit for more powerful chemical propulsion.

NASA in May announced a contract with the company to vet its thrusters for potential small satellite propulsion, and that same month Astro Digital announced Phase Four will supply thrusters for planned additions to the California-based Earth-imaging company’s Landmapper data-collection constellation. Halpern said “our systems are ready for mass manufacture” at the Phase Four El Segundo facility, and his company will unveil more details about the thruster designed for cubesats “by the end of 2018.”

Certain types of propulsion don’t scale down economically for cubesats and small satellites, but decisions made by satellite makers will depend on the mission demands, said Timothy Smith, space propulsion project manager at NASA’s Glenn Research Center in Cleveland.

“Sometimes you might want to get where you are going really fast and would want a chemical thruster, but then you could be out of fuel,” Smith said. “Or you could have a few different types of electrical propulsion to choose from. There are a lot of tradeoffs to look at to narrow it down.”

The Phase Four photo is of a Phase Four radio frequency plasma thruster firing in a vacuum chamber.