The American space agency’s Marshall Space Flight Center recently signed a $18.8 million contract with BWXT Nuclear Energy for a “highly efficient, high-thrust engine” concept - to potentially take future crewed missions to Mars and beyond. The design and testing project will run through 2019 subject to Congressional approval.
NASA scientists hope the rocket engine will be much more efficient than traditional chemical propellant engines. The Nuclear Thermal Propulsion (NTP) concept could use nuclear fission of low-enriched uranium to heat hydrogen, firing it from the exhaust to create huge amounts of thrust.
An NTP engine could have double the propulsion efficiency of the Space Shuttle’s main engine, reducing a trip to Mars from six to four months, NASA said.
However, a heavy nuclear reactor and large fuel tanks for the relatively low-density hydrogen could reduce some of the potential benefits, said aerospace engineer Mark Hempsell.
“You need to use hydrogen propellant and that means the tanks tend to be a lot heavier than they would otherwise tend to be,” said Hempsell, who is also president of the British Interplanetary Society (BIS), to Professional Engineering. “A lot of the advantages tend to disappear a little when you get down to looking at the detail.”
NASA's claim that shorter trip times would mean less radiation exposure for astronauts and reduced weight is also flawed, Hempsell said, as radiation from the nuclear reactor would require heavy shields.
The rocket could nonetheless hit ultra-fast velocities of 12km/s if NASA and BWXT adapted a concept developed by British engineer Alan Bond, Hempsell said. While working for Rolls Royce in the 1970s, Bond proposed an engine system using the nuclear reactor to create an electrical “arcjet”. The electricity would impart more energy to the heated gas, increasing its exit speed and creating more thrust – “then you are really humming,” said Hempsell.
However, he said the Nasa concept will still have performance advantages compared to chemical propellant alternatives.
The NTP “could open up deep space for human exploration,” said NASA aerospace engineer and NTP project manager Sonny Mitchell. “As we push out into the solar system, nuclear propulsion may offer the only truly viable technology option to extend human reach to the surface of Mars and to worlds beyond.”