A rotating detonation engine (RDE) is a type of engine that generates thrust by channeling a continuous, supersonic explosion around a ring-shaped chamber instead of burning fuel the way conventional engines do. Where a traditional jet engine or rocket relies on relatively slow, steady combustion, an RDE harnesses detonation, a far more violent and efficient process that releases energy almost instantaneously. The result is an engine that can theoretically extract significantly more work from the same amount of fuel, with fewer moving parts.
How It Works
The core of an RDE is an annular combustion chamber, essentially two concentric cylinders forming a narrow ring-shaped gap. Fuel and oxidizer enter axially through one end of this ring. Once ignited, the mixture doesn’t simply burn. It detonates, producing a shock wave that races around the circumference of the chamber at supersonic speed. This wave continuously sweeps through fresh fuel as it circles, sustaining itself without needing to be reignited.
The cycle has three stages. First, the detonation wave hits a pocket of fresh fuel-oxidizer mixture and combusts it almost instantaneously in what engineers call constant-volume heat release. Second, the hot combustion gases expand and blow down through the open end of the annulus, accelerating as they exit to produce thrust. Third, while those spent gases are leaving, new fuel and oxidizer flow in behind them to refill the space before the detonation wave comes back around again. This entire process repeats thousands of times per second as the wave continuously laps the chamber.
The key distinction is that the detonation wave travels circumferentially (around the ring) while the combustion products exit axially (out the back). This means thrust generation is continuous, not pulsed, even though each tiny pocket of fuel experiences an instantaneous detonation event.
Why Detonation Beats Deflagration
Conventional jet engines and most rockets use deflagration, a subsonic burning process where fuel combusts at constant pressure. This follows what’s known as the Brayton cycle. An RDE instead approximates the Humphrey cycle, where heat release is accompanied by an increase in pressure due to volumetric confinement. That pressure boost is essentially free energy that a conventional engine leaves on the table.
The efficiency gains are most dramatic at lower compression ratios. Analysis of detonation-based cycles shows thermal efficiency starting around 42% for hydrogen-air mixtures at a compression ratio of 1, climbing to a peak of roughly 66% at a compression ratio of 7. A Brayton cycle engine at those same low compression ratios performs far worse, only surpassing detonation-based efficiency at compression ratios above 23. For applications where you can’t afford a massive, heavy compressor (think missiles, upper-stage rockets, or compact power units), this advantage is substantial. You get more thrust or power from less hardware.
Where the Technology Stands
RDE development has accelerated rapidly in recent years, moving from lab curiosities to real hardware producing real thrust.
NASA has hot-fire tested several rotating detonation rocket engines in the 10,000-pound thrust class, running them on multiple propellant combinations including liquid oxygen paired with liquid methane, liquid hydrogen, and RP-1 (a refined kerosene). These tests focused not just on performance but on survivability, determining whether the engine hardware can withstand the punishing conditions inside the chamber over repeated firings.
In May 2025, Houston-based startup Venus Aerospace completed the first-ever test flight of a rotating detonation rocket engine in the United States. A small rocket equipped with their engine launched from Spaceport America in New Mexico, marking the transition from ground testing to actual flight. DARPA is also investing through its Gambit program, which aims to develop RDEs as propulsion for standoff strike weapons launched from fourth-generation fighters, targeting time-critical threats at what the agency calls “campaign scale,” meaning large numbers produced affordably.
The Hardest Engineering Problems
Sustaining a continuous detonation wave inside a metal chamber creates extreme thermal loads. The wave generates temperatures and pressures that can destroy engine walls in seconds without active cooling. Research at Purdue University has explored regenerative cooling, where the fuel itself (often hydrogen) flows through channels in the chamber walls before being injected and burned. This approach shows promise: wall temperatures remain manageable, coolant temperature rise stays low, and the pressure drop through the cooling jacket is acceptable, even when engineers assume worst-case heat flux levels throughout the chamber.
Wave stability is the other major challenge. The detonation wave needs to propagate smoothly and predictably around the annulus. In practice, the design of the fuel injectors has an enormous influence on behavior. When fuel enters through discrete injector holes rather than a continuous slot, acoustic reflections from the wave passing over each injector opening can spawn secondary waves. These secondary waves travel in various directions, sometimes counter to the primary wave, and affect its speed, strength, and stability. Reducing the number of injectors increases variability in wave speed and can destabilize the combustion mode entirely. Getting the diameter, spacing, and number of injectors right is one of the most active areas of RDE research, because small changes in injector geometry can mean the difference between a single clean detonation wave and a chaotic mess of competing waves that degrades performance.
Applications Beyond Rockets
While rocket propulsion gets the most attention, RDE technology could reshape land-based power generation. Gas turbines that produce electricity today run on the Brayton cycle, and replacing their conventional combustors with rotating detonation combustors could meaningfully improve thermal efficiency. This is particularly appealing in an energy landscape focused on decarbonization, since extracting more useful energy from each unit of fuel directly reduces emissions per kilowatt-hour generated.
For aerospace, the applications span a wide range. Compact, efficient RDEs could power hypersonic cruise missiles that need to cover long distances without carrying excessive fuel. They could serve as upper-stage rocket engines where every pound of propellant saved translates to more payload in orbit. And because the combustion process is mechanically simple (no turbines, no complex valve timing), RDEs could eventually be manufactured at lower cost and higher reliability than the turbomachinery-heavy engines they replace.
How RDEs Compare to Pulse Detonation Engines
Rotating detonation engines are sometimes confused with pulse detonation engines (PDEs), which also use detonation rather than deflagration. The difference is in how the detonation is sustained. A PDE fires in discrete pulses: fill a tube with fuel, detonate it, purge the tube, refill, repeat. This cycling limits how fast the engine can operate and creates an inherently unsteady thrust output. An RDE sidesteps this entirely by keeping the detonation wave in continuous motion around the annular chamber. There’s no need to stop, purge, and restart. The wave just keeps going as long as fresh fuel is supplied, producing steady thrust with a simpler mechanical design.