NASA has achieved a new milestone in developing an innovative propulsion system that could enable more efficient and powerful missions to the Moon and Mars. The system, called the Rotating Detonation Rocket Engine (RDRE), uses a novel combustion technique that produces supersonic flame fronts and generates more thrust with less fuel.
Engineers at NASA’s Marshall Space Flight Center in Huntsville, Alabama,conduct a successful,251-second hot fire test of a full-scale Rotating Detonation Rocket Engine combustor in fall 2023,achieving more than 5,800 pounds of thrust.
Engineers at NASA’s Marshall Space Flight Center in Huntsville, Alabama, successfully tested a 3D-printed RDRE for 251 seconds (or longer than four minutes), producing more than 5,800 pounds of thrust. That kind of sustained burn emulates typical requirements for a lander touchdown or a deep-space burn that could set a spacecraft on course from the Moon to Mars, said Marshall combustion devices engineer Thomas Teasley, who leads the RDRE test effort at the center.
The RDRE is based on the principle of detonative combustion, which differs from the conventional deflagrative combustion used in most rocket engines. In deflagrative combustion, the fuel and oxidizer are mixed and ignited, creating a subsonic flame front that propagates through the combustion chamber. In detonative combustion, the fuel and oxidizer are injected into an annular channel, where they are ignited by a spark plug and form a supersonic shock wave that travels around the channel, compressing and detonating the mixture. The resulting high-pressure and high-temperature gases are then ejected through a nozzle, creating thrust.
Detonative combustion is more efficient than deflagrative combustion, as it allows for a higher specific impulse (a measure of thrust per unit of propellant) and a lower fuel-to-oxidizer ratio. However, detonative combustion is also more challenging to achieve and control, as it requires precise timing and injection of the fuel and oxidizer, as well as a stable detonation wave that does not extinguish or transition to deflagration².
To overcome these challenges, NASA engineers used additive manufacturing, or 3D printing, to create the RDRE combustor. The 3D-printed combustor is made of a copper alloy called GRCop-42, which was developed by NASA’s Glenn Research Center in Cleveland, Ohio, and can withstand the extreme heat and pressure generated by the detonations. The 3D-printing process also allows for the creation of complex geometries and subscale injector orifices that are difficult to manufacture using conventional methods.
The RDRE test was conducted in fall 2023 at Marshall’s Test Stand 115, which is specially designed to handle high-pressure and high-temperature rocket engines. The test was a collaboration between NASA, In Space LLC, and Purdue University, both of Lafayette, Indiana. In Space LLC provided the RDRE hardware, while Purdue University provided the fuel and oxidizer delivery system and the data acquisition system.
The test was the second hot fire test of the RDRE, following the first one that was performed in summer 2022, which produced more than 4,000 pounds of thrust for nearly a minute. The primary goal of the latest test, Teasley noted, is to better understand how to scale the combustor to different thrust classes, supporting engine systems of all types and maximizing the variety of missions it could serve, from landers to upper stage engines to supersonic retropropulsion, a deceleration technique that could land larger payloads – or even humans – on the surface of Mars.
“The RDRE enables a huge leap in design efficiency,” Teasley said. “It demonstrates we are closer to making lightweight propulsion systems that will allow us to send more mass and payload further into deep space, a critical component to NASA’s Moon to Mars vision.”
The RDRE is managed and funded by the Game Changing Development Program within NASA’s Space Technology Mission Directorate. NASA’s Glenn Research Center and Venus Aerospace of Houston, Texas, are also working with NASA Marshall to identify how to scale the technology for higher performance.