Thursday, June 18, 2020

DARPA is Reviving NERVA - What?

It's a rule of writing for others to never use acronyms without explaining them.  Fully spelled out (so that it would be a two-line title) the Defense Advanced Research Projects Agency (DARPA) is opening bidding for contracts to revive the Nuclear Engines for Rocket Vehicle Applications (NERVA) program from the early days of NASA.

The basic problem is that moving things around in space is slow, ultimately because every molecule of fuel has to be lifted with you (for now) so using small amounts of fuel and taking a long time to get anywhere is a reasonable trade.  The idea of nuclear powered propulsion goes back to the earliest days of NASA.  Wernher von Braun, the German engineer who defected to the United States after World War II, started a program to develop systems before the moon landings.  That program, NERVA, eventually got closed down to help pay for the Shuttles.  See here for a NASA review of the program (pdf) and here for a video of a test firing
But now, the US Department of Defense is getting interested in space-based propulsion. Last month, through a presolicitation, the US Defense Advanced Research Projects Agency announced its intent to have a flyable nuclear thermal propulsion system ready for a demonstration in 2025.

Through this Demonstration Rocket for Agile Cislunar Operations, or DRACO program, the defense agency seeks technology that will allow for more responsive control of spacecraft in Earth orbit, lunar orbit, and everywhere in between, giving the military greater operational freedom in these domains.

"Activity in cislunar space is expected to increase considerably in the coming years," Maj Nathan Greiner, manager of the DRACO Program, told Ars. "An agile nuclear thermal propulsion vehicle enables the DOD to maintain Space Domain Awareness of the burgeoning activity within this vast volume."
There are a few ways to achieve nuclear propulsion; the most accessible (and probably the most politically acceptable) is nuclear thermal power in which a reactor super heats a fuel (probably hydrogen gas) and it expands through a nozzle.
In "Phase 1" of its solicitation, DARPA has asked industry for the designs of both a nuclear thermal reactor and an operational spacecraft upon which to demonstrate it. This initial phase of the program will last 18 months. Subsequent phases will lead to detailed design, fabrication, ground tests, and an in-space demonstration. No contracts have yet been awarded, and award values will be determined by industry submissions.

With the DRACO program, the US Defense Department could potentially move large satellites quickly around cislunar space. For example, moving a 4-ton satellite from point A to point B might take about six months with solar electric propulsion, whereas it could be done in a few hours with nuclear thermal propulsion.
It's arguable that this DARPA action is being brought along by other trends going on.  First is the creation of Space Force and the recognition of the value of the High Frontier.  Second, critical enabling technologies are maturing at the right times, such as better refractory materials (able to handle extreme temperatures); in a nuclear thermal engine, Hydrogen is stored at 19 Kelvin, while "the other end" of the reactor has hydrogen heated to 2500 Kelvin - or higher.  Third, NASA is working with BWX Technologies, the company which makes most of the nuclear reactors found on US Navy submarines and aircraft carriers, on the design of a reactor for Mars missions.

1960s artist's concept of a nuclear thermal rocket arriving at Mars.  The circular structure on the left is an aerobrake. 

DARPA has a reputation for producing some of the leading edge technologies in the world.  It seems they've decided the time is right to push this one along. 


  1. It's a good thing, finally. Heinlein's torchships!

    NERVA is a rather elegantly simple idea. Run water through a reactor, heats up, expelled rearward as a gas or plasma (radioactive gas or plasma.) All you need are radiators to suck the excessive heat off, good radiation shielding, staying out of the radioactive area and staying in the protected cone, and lots of water or other fuel to turn into gas or plasma.

    Gas is doable right now, has been since the 60's. Flashheat water into vapor provides a nice boost.


    The real energetic propulsion is to heat up the propellant to a plasma state, which will give much more thrust per mass/volume of propellant.

    For a good in-depth view of space travel, atomic rockets, war in space, habitats and a complete fragging of most Sci-Fi spaceships, go to Atomic Rockets. Neat website:

    Seriously, if you've never seen this site before, or if you haven't been to it in a long time, prepare for a deep dive into the joys of real space ships, real engines, real everything.


    (Dances in Fahrenheit)

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  4. Wonder if SpaceX will be applying?

  5. Water as a reaction mass makes sense. Finding a nice water asteroid that we could park in orbit around the Moon and mine would speed things up - but you have to find one and then move it.

    1. The original "Atomic Rocket" in Destination Moon used water as the reaction mass. The reactor turned the water into "Superheated Steam" per the movie.

    2. Once you have found it and have atomic rockets to move it, it just becomes an exercise in math. Complicated, but easy with enough computing power. A smartphone would likely suffice if you weren't in a huge hurry and had the right software.

  6. If NASA does nuclear rockets, then the competitors to NASA are banned again due to government's monopoly on things nuclear. Plus then the price goes up again because woo-woo nuclear scary. Government's political-economic goal here is like Apollo -- make government liked and important and generating awe while removing money from the middle class which the peasants would otherwise use to make themselves less dependent on government.

  7. Everything old is new again. A bit of 60's style propaganda, but with real science and actual footage of several nuclear thermal test rocket engines from the late 50's to the late 60's.
    About 23 minutes run time.

    1. Thanks for the link. It's definitely worth the time to watch. Full of that '60s "we can do anything" vibe that we don't see much of these days.