Los Alamos NERVA: The American Nuclear Engine That Could Have Taken Humans to Mars

The age of nuclear fusion may soon be upon us if recent advancements are anything to go by. What this means for the future of space travel has yet to reveal itself. But make no mistake, nuclear-powered spacecraft engines are nothing new. Albeit, powered by fission, not fusion.
NERVA Engine Test 19 photos
Photo: NASA
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We don't blame you if you're shocked the United States wielded a nuclear spacecraft engine as far back as the 1960s. You're probably even more shocked that hardly anyone remembers it. The Nuclear Engine for Rocket Vehicle Application (NERVA) project would've been nothing short of a crown jewel program for any other research team. But not for New Mexico's Los Alamos Laboratories.

That's right; the NERVA engine was developed by the same team who brought the world the first nuclear-fission weapons. The very same that helped end World War II. If there was ever a project substantial or significant enough to overshadow literal nuclear rocket engines, that certainly fits the description. For Los Alamos scientists and engineers, it makes sense the first logical step post-Manhattan Project would be in the direction of rocket engines.

Come the end of the Second World War, novel German rocket science from future NASA personnel like Wernher Von Braun was now in the hands of the Americans. But while the V2 chemical rocket was nothing short of witchcraft to average folks in the mid-1940s, it wouldn't be long for experts to ask if there was another, more powerful means of fueling rocket engines.

In the following decade, a torrent of proposals across America for nuclear-powered planes, trains, and automobiles defined the 1950s as the start of the atomic era. Right alongside preposterous ideas like Ford's Nucleon passenger car was one of the first working concepts for a nuclear fission-powered thermal rocket. One that, in theory, could provide power and fuel economy no traditional chemical rocket could ever dream of.

NERVA rocket
Photo: NASA
With the oversight from Los Alamos Labs, an engineering group was assembled consisting of personnel from the Aerojet group of Rancho Cordova, California, for the rocket engine portion. Meanwhile, the all-important reactor portion was trusted to the Westinghouse Astronuclear Laboratory outside Pittsburgh, Pennsylvania. Though simple in concept, when is nuclear physics ever simple?

That said, the bare basics of the NERVA engine are easy to understand. In truth, NERVA operated much in the same manner as a chemical rocket. A typical chemical propellant, usually cryogenic hydrogen, was introduced to a nuclear reactor undergoing critical fission inside a combustion chamber. The resulting reaction is channeled out a rocket nozzle to generate very high propulsive thrust.

The NERVA engine consisted of very few moving parts. The most obvious among them was a series of turbopumps that kept cryogenic hydrogen flowing through nuclear fuel rods. Otherwise, the sheer energy emitted from the nuclear reactor essentially did most of the hard work itself. Said turbopumps act on the same mechanical principle as a turbocharger in a sports car, except with super-chilled hydrogen instead of exhaust gasses.

Each fuel rod consisted of powdered graphite and Uranium formed into shape with special machinery. The granite portion acted as what's referred to as a moderator. A layer of material that keeps fission reactions from spiraling out of control or going "supercritical" by impeding the travel path of atomic particles flung in all directions during fission. With dimensions of 6.9 meters (23 ft) long and 2.59 meters (8 ft 6 in) in diameter, NERVA's later, more powerful iterations were no puddle jumper in size.

NERVA rocket
Photo: NASA
Inside NERVA's combustion chamber, an internal shield surrounded the piping-hot reactor. This shield consisted of a layer of beryllium metal that acted as a reflector. I.e., another layer of material that inhibits or reflects the speed and direction radioactive particles travel during fission. As the super-chilled hydrogen continued to flow through each fuel rod's infernally hot channels, the energy released increased dramatically. Thus resulting in very high thrust. Its working principle is much the same as a nuclear fuel rod immersed in water and connected to a steam turbine here on Earth.

Though any number of nuclear isotopes could theoretically do the job, Los Alamos Labs and Westinghouse chose enriched Uranium-235 for the NERVA application. This choice was made because U-235 is lighter and less prone to super-criticality than its Uranium-238 cousin. As a result, it has the potential for an incredibly high measurement of what rocket scientists call a specific impulse.

With the potential to heat hydrogen fuel to 2,400 Kelvin (3860.3°F, 2126°C), the NERVA engine could have provided American spacecraft with exceptional performance while not being so wasteful that it couldn't conserve fuel for an entire mission. The potential for space exploration seemed palpable during the NERVA development. Be it traveling to near planets like Mars and Venus or even places farther off like the Asteroid Belt. It was all suddenly theoretically possible.

In August 1960, the recently formed NASA established the Space Nuclear Propulsion Office with the sole purpose of overseeing the NERVA program and any developments made afterward. With offices in Germantown, Maryland, Cleveland, Ohio, and Albuquerque, New Mexico, the resources and personnel required to keep the program running spanned the continental U.S.

NERVA rocket
Photo: NASA
Six NERVA technology demonstrators were built between 1964 and 1973. The highest power threshold NASA could muster during testing was a scarcely believable 246,663 newtons (55,452 lbf) of thrust and a specific impulse of 710 seconds (7.0 km/s) in the NERVA  Alpha variant. This engine could theoretically operate in deep space and maintain this level of thrust throughout the duration of a space mission. So you can only imagine what NASA may have had planned.

Records indicate Wernher Von Braun envisioned a successor booster rocket to the Saturn V, called the Nova series. Had it been built, the nuclear/chemical hybrid rocket would have joined the Space Shuttle in a spacecraft fleet that would have been nothing short of astonishing. One can only imagine how humans could have landed on the surface of Mars by the early 1980s had everything gone to plan.

It's all the more reason why the program's cancelation under the Richard Nixon administration in 1973 hurt almost as much as axing the Apollo program just the year before. It was the last nuclear thermal rocket project of great significance for fifty years and counting. That said, now that the American National Ignition Facility just cracked out 1.5 megajoules through nuclear fusion, don't be surprised if things start to pick up again sooner than you think.

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