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SpaceTech Briefs: NASA Teams with DARPA for Nuclear Engine, Tests Revolutionary Deep Space Propulsion System

By Doug Messier
Parabolic Arc
February 13, 2023
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SpaceTech Briefs: NASA Teams with DARPA for Nuclear Engine, Tests Revolutionary Deep Space Propulsion System
Artist concept of Demonstration for Rocket to Agile Cislunar Operations (DRACO) spacecraft, which will demonstrate a nuclear thermal rocket engine. Nuclear thermal propulsion technology could be used for future NASA crewed missions to Mars. (Credit: DARPA)

NASA & DARPA Team to Demonstrate Nuclear Engine

NASA and the Defense Advanced Research Projects Agency (DARPA) are teaming to conduct a demonstration of a nuclear thermal rocket engine in space that could be three times more efficient than conventional chemical propulsion.

The Demonstration Rocket for Agile Cislunar Operations (DRACO) program aims to develop a nuclear thermal rocket that will allow for faster travel times to Mars to reduce risks to astronauts and the amount of supplies spacecraft will need to carry.

NASA will lead technical development of the nuclear thermal engine. DARPA will lead the overall program, including spacecraft development, rocket systems integration and procurement, approvals, scheduling, security, safety, liability, and engine integration.

A nuclear thermal rocket engine uses a fission reactor to generate extremely high temperatures. The engine transfers the heat produced by the reactor to a liquid propellant, which is expanded and exhausted through a nozzle to propel the spacecraft.

NASA and other government agencies pursued the development of the Nuclear Engine for Rocket Vehicle Application (NERVA) from 1957 to 1973. The nuclear thermal engine program was canceled in January 1973 for budget reasons after the expenditure of $1.4 billion.

You can read more about the program here.

NASA Validates Rotating Detonation Rocket Engine

Credit: NASA

A team of propulsion development engineers at NASA’s Marshal Space Flight Center has developed and tested the space agency’s first full-scale rotating detonation rocket engine (RDRE), which could lead to significantly improved propulsion systems for deep-space missions.

RDRE generates thrust using a supersonic combustion phenomenon known as a detonation. NASA didn’t provide a good explanation for how the engine works. But, I did find one from JAXA, which tested a RDRE on a S-520 sounding rocket in July 2021.

“Detonation” refers to when the flame front in the ignited fuel-oxidizer mixture moves so fast that it surpasses the speed of sound. Normally, the expansion of burned gases behind the on-coming flame would cause the unburned fuel-oxidizer mixture to move outwards. But the progression of the flame front during a detonation is so rapid that there is no time for the unburned mixture to get out of the way. Instead, the pressure and temperature leap upwards while the volume rapidly decreases. The is referred to as a detonation shock wave.

Burning the fuel-oxidizer mixture before it expands leads to fast and efficient combustion, as the denser fuel-oxidizer mixture can be burned rapidly. However, the detonation wave would usually shoot out the rocket engine with the combustion products and have to be restarted.

But continuously restarting the igniting detonation wave is avoided in a Rotating Detonation Engine System by confining the wave to travel around an open-ended cylindrical chamber. Travelling in a circle, the wave continuously ignites fresh fuel-oxidizer mixture as it is fed into the chamber. As the detonation wave repeatedly slams through the fuel on its circular path, rapid combustion occurs and the resulting products expand upwards and accelerate out the chamber end to generate thrust.

Rotating detonation rocket engine, or RDRE hot fire test at Marshall Space Flight Center. (Credits: NASA)

RDRE produces more power while using less fuel than today’s propulsion systems and has the potential to power both human landers and interplanetary vehicles to the Moon, Mars and deep-space destinations.

RDRE was fired more than a dozen times over a duration of nearly 10 minutes last year at Marshall’s East Test area. Engineers at Marshall and IN Space LLC of West Lafayette, Ind., are confirming data from the hot fires. RDRE demonstrated that its 3D printed hardware could operate for long durations while withstanding the extreme heat and pressure environments generated by detonations.