Officially, NASA has been charged with sending astronauts to Mars sometime in the 2030s. Toward that end, according to a Friday story in Universe Today, space agency engineers at the Marshall Space Flight Center are looking at an old concept for interplanetary travel, nuclear thermal engines. However, some doubts have been expressed whether NASA will be granted the budget to develop such engines.
A nuclear thermal rocket uses a nuclear reactor to superheat liquid hydrogen into plasma that is then channeled through a nozzle to generate thrust. The amount of thrust generated is far greater than can be achieved with a chemical rocket. Trip times to Mars would be reduced by about half.
NASA looked at NTRs in the 1960s and early 1970s as part of the Rover and NERVA programs. Various rocket engines were ground tested with good results. However, the program was shut down after a prospective Mars mission to have taken place in the 1980s was postponed indefinitely. The concept made a brief reoccurrence during President George H. W. Bush’s Space Exploration Initiative, but then fell by the wayside when it too was canceled.
Besides a humans to Mars expedition, nuclear rockets could be used to deliver heavy payloads to a variety of destinations. One concept would be to use an NTR as the upper stage of a heavy-lift Space Launch System. The SLS would deliver the upper stage and its payload to low Earth orbit. Then the nuclear reactor would be activated and would blast out of the Earth’s gravity well. Huge probes to the moons of the outer planets and cargo to the surface of Mars could be delivered, as a result.
Dr. Robert Zubrin, a long-time advocate for the exploration and eventually colonization of Mars, notes that NASA engineers have some good ideas. What they lack, however, is money.
“Nuclear Thermal Propulsion (NTP) offers significant benefits for human Mars exploration missions. Unfortunately, since the Obama administration has no commitment to go to Mars, it has no serious effort to develop NTP. The NASA engineers quoted in this article have very good ideas. But they have very little funds to implement them.”
If course, if the current president is uninterested in such things, some of the new space leadership in Congress may well be. Rep. John Culberson, the new chairman of the House Appropriations subcommittee that funds NASA, is a big champion of sending a probe to Europa. An NTR upper stage for the SLS would serve that purpose rather well.