NASA, DARPA Award Contract for Nuclear Powered Rocket

NASA and DARPA announced Wednesday that they had awarded a contract to Lockheed Martin and BWX Technologies to build and develop a nuclear thermal rocket (NTR) engine.

Lockheed Martin and BWX technologies under DARPA’s DRACO (the Demonstration Rocket for Agile Cislunar Operations) program and in partnership with NASA will build the nuclear thermal rocket. NASA and DARPA are committing up to $499 million towards this program.

Lockheed Martin (locally known as Lock-Mart) will serve as the primary contractor to assemble the eXperimental Nuclear Thermal Reactor vehicle (X-NTRV) and its engine. BWX Technologies will develop the nuclear reactor and fabricate the High-Assay Low-Enriched Uranium (HALEU) fuel to power the reactor.  The targeted date for the launch is four years from now, so NET 2027.  

While the overall size of this test bed was not revealed, during a press conference today, Dr. Tabitha Dodson of DARPA said it would not require a heavy lift vehicle and be able to fit in the fairing of a SpaceX Falcon 9 or United Launch Alliance Vulcan Centaur.

The need for faster transport around the solar system has come up before.  Currently, everything we launch gets there on chemical propulsion.  They're great for getting payloads into space, but they gulp large amounts of fuel and then they're done.  Everything that has visited or orbited around the planets now and the few that have left the solar system got their start that way, but for Mars, for example, the world waits for a short period every two years when our orbit is going to overtake Mars in its orbit.  We fling a payload in that direction and wait six months for it to get there.  Worse, if travelers to Mars need to evacuate it could take them over a year to get back to Earth depending on when they leave.  It has been concluded nuclear power is the only realistic way to do such missions.  It gets more convincing for the outer planets.

The promise of nuclear power is twofold.  First and foremost, the potential for cutting travel time by slow but steady acceleration from running the engine continually is there.  Second, the inertia from the acceleration of an engine could give some semblance of artificial gravity reducing the crew's physical deterioration from Zero-G.  Or, at least making it more manageable. 

Conceptual rendering of DARPA’s DRACO - Image credit to DARPA  With no sense of scale, it helps to know that they say the system you see there would fit in the payload fairing of a Falcon 9 or Vulcan Centaur. 

The concept behind a Nuclear Thermal Rocket (NTR) is simple.  The nuclear fuel is simply a heater that heats a propellant.  There is a propellant, liquid hydrogen, but no oxidizer and no combustion.  The hydrogen is flashed into the hot area and a nozzle, where it's then heated from 20 Kelvin, 20° above absolute zero, to 2,700 Kelvin in less than a second.  The hydrogen expands dramatically from the heating.  No combustion means the thrust is from the momentum transfer of the hydrogen atoms being blown out the nozzle.  Dr. Dodson of DARPA points out that the NTR achieves a high thrust similar to chemical propulsion but is two to three times more efficient.

These engines have been theoretically understood and modeled since the 1960s NERVA programs (Nuclear Engines for Rocket Vehicle Application).  They have never been tested in space, though, which means there are plenty of other concerns, including regulatory.  The reactor has to be capable of being completely off from launch until it has achieved a designated safe orbit.  

This final orbit has yet to be determined, but it is likely to be 700 to 2,000 km above the surface of the Earth, such that the vehicle's reentry into the planet's atmosphere will take place hundreds of years after any nuclear reactions occur.

To be complete, this is a test program there are things about reactors in space (and microgravity) that have never been tested in space.  This is very experimental.

"It's important to keep in mind that this is a demonstration engine," Dodson said. "And just like any other test of a rocket engine, NASA may need to do a series of follow-on engine development work in order to get closer to their perfect operational engine."

A big unknown is the ability to keep liquid hydrogen cold for long periods.  20K is extremely cold and it has never been successfully stored in space for more than "days" at a time. 

Until now, liquid hydrogen has only been successfully stored in space for days since it boils above the extremely cold temperature of 20 Kelvin. Dodson said this mission would attempt to store liquid hydrogen in its ultra-cold state for a couple of months, allowing enough time for multiple tests of the nuclear thermal engine.

After the propellant runs out, the engine will no longer be able to operate, even though mission controllers on the ground will still retain communication with the spacecraft. The mission could be extended if it could be robotically refueled, and Dodson said the spacecraft designers are attempting to allow for this possibility.

I'd really like to see this thing work.  Decades ago, I read of using engines like this to allow constant acceleration to keep the explorers at 1g gravity while traveling.  That would eliminate the concerns with zero-G affects on bones and muscles as well as drastically decrease the time traveling. There are a lot of hurdles to be overcome before we could be a space-faring civilization; storage of the hydrogen (or another propellant), storage of food, and more, but this is an essential technology.