A student team from ETH Zurich‘s Academic Space Initiative Switzerland (ARIS) has successfully ignited a rotating detonation rocket engine (RDRE) using liquid propellants, recording stable detonation waves during a night test at Dübendorf Airfield in Switzerland.
The achievement, reached by the 20-strong Pegasus team in early April 2026, places the students in rare company: only around a dozen countries have developed and tested such engines, and no other student group had previously demonstrated stable liquid-fueled RDRE operation.
Jan Hofstetter, Project Manager of Pegasus at ARIS, described the result as the product of nearly a year of focused development. Mattia Röösli, a 21-year-old third-year mechanical engineering student who designed the engine’s injector, explained the approach that made it possible: “You don’t need to be exceptionally talented to develop a rocket engine after two years of study. You go step by step and help each other.” Röösli also pushed back against over-preparation, highlighting, “It’s a mistake to think you can fully understand the topic before you start. There are simply far too many unanswered questions.”
Why detonation beats combustion
The engine burns propane and liquid oxygen, with the injector, manufactured using metal additive manufacturing (metal AM), at its core. RDRE technology differs from conventional rocket engines in that the fuel does not burn steadily; instead, it detonates, producing a supersonic wave that rotates continuously around a ring-shaped combustion chamber at up to 20,000 revolutions per second. That detonation cycle yields significantly higher pressures and temperatures than steady-state combustion, allowing the energy in the fuel to be extracted more completely.
The theoretical efficiency gain over conventional engines is estimated at 10 to 20 percent, a meaningful margin given that fuel accounts for 80 to 90 percent of a rocket’s total launch weight.
The Pegasus injector had to mix and deliver propane and liquid oxygen in under a millisecond. One miscalculation and the detonation wave could propagate back into the supply lines. Röösli tackled it through iterative sketching, team review, calculation, and prototyping before advancing to printed metal parts.
Two attempts, three detonation waves
The test itself required two firing attempts. The first, just after seven in the evening, produced ignition but no confirmed detonation wave. The team examined sensor data, adjusted the propane flow parameters, and fired again at quarter to nine. This time the pressure wave shook the door of the control hut, and the high-speed camera confirmed three distinct rotating detonation waves. The result was validated in real time by colleagues watching the footage beside the camera outside the safety perimeter.
The Pegasus engine was built partly within ETH Zurich’s Focus Projects curriculum, a two-semester format in which teams of five to ten students design and produce a working product, and partly through sponsorships and in-kind industrial support. The team also benefited from proximity to a commercial RDRE start-up based in the same ETH hangar at Dübendorf, whose engineers provided informal guidance alongside the coaching passed down from previous ARIS project cohorts.
The Pegasus result matters beyond the immediate milestone. RDREs have attracted sustained research interest from NASA, national laboratories in Poland, and Japan’s space agency, which remains the only organization to have fired such an engine in space.
Metal AM as the Key Enabler of RDRE Development
The Pegasus injector is one example of a wider pattern: across RDRE programs at every level of the industry, metal AM has become the enabling step between concept and working hardware. The geometry these engines demand — tight-tolerance injectors, integrated cooling channels, complex flow paths — cannot be reliably produced through conventional machining, making metal AM a functional prerequisite rather than a design preference.
Astrobotic arrived at the same conclusion through its Chakram RDRE program, where a patented porosity-control printing process co-developed with Elementum3D became the foundation for injector design and thermal management. The engine logged over 470 seconds of total run time at NASA’s Marshall Space Flight Center, including a single 300-second continuous burn believed to be the longest ever recorded for an RDRE — a result its principal investigator attributed directly to what AM made structurally possible.
Venus Aerospace made the same connection at the component level. The company incorporated a NASA SBIR-funded laser powder bed fusion (LPBF)-produced nozzle — produced in GRCop-42 and GRX-810 alloys — into its hypersonic RDRE platform, targeting flight integration across future landers and orbital transfer vehicles. The nozzle’s internal cooling channels and injector orifices could not have been produced any other way.
The pattern is consistent: where RDRE development has moved from paper to hardware, metal AM has been the enabling step. The ETH Zurich result adds student-built hardware to a list that includes commercial ventures and NASA-backed programs alike.
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Featured image shows ETH Zurich’s Academic Space Initiative Switzerland. Photo via ETH Zurich.
