NASA looks at reviving atomic rocket program

When the first manned mission to Mars sets out, it may be on the tail of an atomic rocket engine. The Space Race vintage technology could have a renaissance at NASA after the space agency's Marshall Space Flight Center in Huntsville, Alabama signed a contract with BWXT Nuclear Energy to develop updated Nuclear Thermal Propulsion (NTP) concepts and new fuel elements to power them.

The Apollo missions to the Moon demonstrated many things. They showcased human ingenuity, determination, and courage. They proved what American engineering and industry could accomplish in short order when let loose on a goal and demonstrated that humankind need no longer be confined to a single planet.

Unfortunately, it also showed the fact that chemical rockets, even at the dawn of the conquest of space, had reached their technical limits. True, they could send astronauts to the Moon, but only by using a disposable rocket the size of a skyscraper of which only a capsule with the roominess of an SUV returned. And even this was in no shape for anything except a museum.

Advances in materials technology could lead to the production of LEU NTP fuel elements (Credit: NASA)

What was apparent even in 1969 was that, at the very most, chemical rockets could send an expedition to the planet Mars. However, even this could only be accomplished under the most favorable of conditions and in a configuration that made the voyage little more than a stunt or a protracted suicide mission.

If humanity was ever going to explore and exploit the Solar System in person, a much more powerful propulsion system was needed: an atomic engine.

Atomic or nuclear engines for spacecraft were conceived of almost before the ink was dry on Albert Einstein's famous E=mc² equation. The exploding of the first fission bomb in 1945 and the development of the first power reactors shortly thereafter made the idea seem feasible, and from 1955 to 1972 the US government pursued a test program to create a practical engine.

Some testing can take place in non-nuclear facilities (Credit: NASA)

The reasons for this were obvious. With its higher exhaust velocities and greater specific impulse, a nuclear rocket could carry larger payloads or smaller payloads at greater speeds. Today, as the hazards of spaceflight are better known, such engines are particularly attractive because they could cut months off a trip to Mars, resulting in less exposure time of astronauts to weightlessness and cosmic rays. In addition, once on Mars, the engine's reactor could provide a round-the-clock, high-density power supply for an outpost.

Under the NERVA project, a workable engine was developed, but it was never used on any space mission. Part of the reason was that, though the rocket was twice as efficient as chemical rockets, its need for highly-enriched uranium as fuel, plus its need to operate at temperatures of 3,000 K (2,727° C, 4,940° F), made it the very definition of "risky". Small wonder then that when the Apollo program wound down and the NASA Mars mission was scratched, so was NERVA.

Today, with NASA once again considering the challenges of sending astronauts to Mars, the nuclear option is back on the table as part of the agency's Game Changing Development program. Under this, NASA has awarded BMXT, which supplies nuclear fuel to the US Navy, a US$18.8-million contract running through September 30, 2019 to look into the possibility of developing a new engine using a new type of fuel.

Unlike previous designs using highly enriched uranium, BMXT will study the use of Low-Enriched Uranium (LEU), which has less than 20 percent of fissile uranium 235. This will provide a number of advantages. Not only is it safer than the highly enriched fuel, but the security arrangements are less burdensome, and the handling regulations are the same as those of a university research reactor.

In addition, LEU allows much of the testing of the technology to be done without any fuel at all because the destructive radiation effects are much lower. Also, the initial live engine tests can take place in a single, closed-loop facility that has no outlet to the natural environment.

Key to the concept is the development of an isotopically pure form of tungsten that, mixed with uranium, could be used to create a ceramic-metallic (Cermet) fuel, which would be more stable under the tremendous heat created by the engine.

Under the contract, BMXT and NASA will manufacture and test prototype Cermet fuel elements with 90-percent pure tungsten, as well as look to solve problems in making the fuel, seeing if an LEU engine will have the required thrust, and work on resolving nuclear licensing and regulatory requirements. In addition, BMXT will study the costs of building and operating such an engine.

If NASA determines next month that the LEU engine is feasible, the project will conduct testing and refine the manufacturing process of the Cermet fuel elements over the course of a year, with testing of the full-length Cermet fuel rods to be conducted at Marshall.

The video below outlines the new LEU engine concept.