Juno Propulsion plans first orbital flight of a rotating detonation engine

A new kind of rocket engine heads for orbit

Juno Propulsion, a small aerospace start-up based in Tukwila, Washington, is preparing to fly a rotating detonation engine in orbit for the first time. According to GeekWire, the mission, called Project Iris, is set to launch next year aboard a satellite built by Momentus.

Unlike conventional rocket engines, which burn fuel in a steady flame, Juno's design uses detonation, a combustion wave that travels faster than sound. Harroun describes the result as a more fuel-efficient rocket engine, extracting more energy from the same propellant.

Japan's space agency has tested rotating detonation engines on suborbital research rockets, but Harroun says reaching orbit is a different challenge altogether.

How the NASA prize changed the company

In July 2025, Juno won a NASA prize to fly its engine in space. At the time, the company consisted of Harroun, co-founder and chief technology officer Ari Martinez, and a summer intern, all working from a single-room office.

NASA paid Juno about $500,000 through its TechLeap programme to build the payload. The agency is also covering the Momentus spacecraft and the flight itself. There is no paying customer yet, but the mission is designed to imitate the movements a real satellite would make in orbit.

Harroun recalled the news sinking in weeks later, while camping in Yellowstone and watching satellites pass overhead. She said it felt humbling and exciting to know something the team built would be visible in the sky.

Why detonation engines matter

If Project Iris succeeds, Juno's engines could allow satellites to run on non-toxic fuel and move far more freely in orbit. GeekWire reports that both commercial and defence customers increasingly want this capability.

Harroun points out that handling toxic propellants is so complex that operators can spend more on fuelling a satellite than on the propulsion system itself. She also notes that most satellites have stayed in the orbit a rocket left them in, a limitation better engines could change.

The founder behind the engine

Harroun grew up in Federal Way, south of Seattle, with a physician father and a mother who worked as a flight attendant and flight instructor. She did not come from an aerospace family and did not grow up dreaming of space, but she credits her parents' entrepreneurial example for shaping her path.

She fell for engineering near the end of high school and studied at the University of Washington, spending four years in professor Carl Knowlen's Detonation Engines Lab and leading the propulsion group of the student rocketry team. Internships at NASA, Boeing and Blue Origin followed.

After realising that people in her dream job had studied at Purdue, she spent six years there, earning a master's degree and a Ph.D. in 2023 on the very technology Juno now builds. She met Martinez there, and her doctoral advisor, Stephen Heister, still advises the company and encouraged her to become a founder.

Building a rocket engine company in Seattle

Harroun returned to the Seattle region after finishing her doctorate to start Juno, knowing the local industry from her student days. She says Blue Origin's presence helped create a regional pool of rocket scientists, which made starting a company there an easy decision.

This summer, Juno received a $1.2 million grant from the National Science Foundation, awarded in partnership with Knowlen's research group at the University of Washington. Knowlen said it is exciting to see the early lab research turn into something that will fly in space.

Juno's stated mission is to become the rocket engine provider for the United States, a role Harroun compares to Rocketdyne, the historic engine maker now part of L3Harris. The company plans to start with in-space propulsion for satellites, then expand into upper stages, orbital transfer vehicles and eventually boosters.