Engineers have developed some truly impressive rockets over the decades, including the Saturn V that sent men to the moon. However, they’ve all been chemical rockets, which need an enormous amount of fuel just to slip the bonds of gravity and reach orbit. As NASA sets its sights on more distant goals like Mars, there’s renewed interest in a Nuclear Thermal Propulsion (NTP) system. NASA has partnered with BWXT Nuclear Energy to develop one.
NASA began researching atomic rocket engines in the early 1950s, designing the Nuclear Engine for Rocket Vehicle Application (NERVA). The concept offered a number of intriguing improvements over chemical rockets. It used a nuclear reactor to heat liquid hydrogen to a high temperature, causing it to expand out of the nozzle to produce thrust. It was twice as efficient as the best rocket engines of the day, and offered much higher overall speeds. A flight that would take 8-9 months with a chemical engine might only take 3-4 with the NERVA. However, the engine operated at temperatures nearing 5,000 degrees Fahrenheit (2,700 degrees Celsius) and relied upon highly enriched uranium to power the reactor. The project was scrapped in the early 1970s.
An atomic rocket has the potential to move more mass a much greater distance than traditional chemical propulsion. SpaceX will have its Falcon Heavy rocket in service within a year or two, making it the most powerful launch platform since the retirement of NASA’s Saturn V. But even the Falcon Heavy will only be able to lift 37,000 pounds (16,800 kg) to Mars. A completely empty Dragon 2 capsule weighs in at 14,000 pounds, leaving little room for all the necessities a human expedition would need. Some have proposed sending unmanned missions ahead of humans to deliver supplies, but that pushes back launch timelines and adds to the cost.
NASA’s revival of the NTP idea comes at a time when nuclear technology is much less “blunt” than it once was. The $ 18.8 million contract awarded to BWXT will allow the company to explore the use of Low-Enriched Uranium (LEU) to power a reactor. LEU contains much less fissile uranium 235 than highly enriched fuels, so it’s safer to work with and can’t be used to create nuclear weapons.
BWXT plans to merge the LEU with pure tungsten to create a new ceramic-metal material known as a cermet (see image at top). This would stabilize the fuel and make it safer at the incredibly high temperatures at which such an engine would operate.
NASA will decide next week if the initial NTP proposal from BWXT is strong enough to proceed. If it gets the go-ahead, the company will begin producing the cermet material over the next year, with tests of the engine to follow at NASA’s Marshall Space Flight Center in Huntsville, Alabama.