NASA is refocusing its Project Prometheus nuclear initiative on meeting the surface-power needs of astronauts sent to the Moon and Mars for extended stays.
The shift amounts to a fundamental restructuring of a program initiated in 2002 expressly to develop nuclear power and propulsion systems for unmanned missions to the outer reaches of the solar system. NASA had intended to try out those systems for the first time on a multi billion-dollar orbiter it planned to launch by 2015 for a lengthy tour of Jupiter’s icy moons.
Under the new plan, development of the nuclear electric propulsion system needed for the Jupiter Icy Moons Orbiter (JIMO) mission becomes NASA’s lowest nuclear priority, superseded by surface-power generation and nuclear thermal propulsion.
NASA Administrator Mike Griffin announced the changes to Project Prometheus at a May 12 Senate Appropriations hearing on the U.S. space agency’s 2006 budget request.
“We cannot effectively explore space without nuclear power and, in the longer run, nuclear propulsion,” Griffin told the Senate Appropriations commerce, justice and science subcommittee. “But having taken JIMO off the plate, the proper ordering of priorities now changes. The first thing we will need is surface nuclear power for our astronauts when they return to the Moon in a decade or so. Nuclear thermal propulsion will be the next step. A nuclear upper stage is the best way to take humans to Mars . . . finally, the last priority would be nuclear electric propulsion, which was linked to JIMO. It will be useful for cargo missions to Mars, but well after we start sending humans there.”
After the hearing, Griffin told reporters that when he says NASA needs surface nuclear power, he is talking about reactors, not just radioisotope thermoelectric generators (RTGs), like those that provide modest amounts of electrical power for the Cassini spacecraft, which is exploring Saturn and its moons.
Griffin said that while RTGs provide adequate power for planetary probes and robotic rovers, and will remain in use for the foreseeable future, they do not come close to meeting the power requirements for the human expeditions called for in NASA’s new exploration strategy.
“Prometheus must include the development of a reactor for lunar and other space, other power supply missions,” Griffin said. “RTGs furnish power on the order of a 100 watts . . . that won’t run your hairdryer. I mean, it’s pathetic.”
Griffin said solar power alone probably will not prove adequate for lunar expeditions of more than 20 days duration.
“If you want to go to the Moon and stay for a couple of weeks and maybe a few extra days you can probably do that on fuel cell power [and] solar power arrays,” Griffin said. “If you want to stay through the two-week lunar night, one can concoct schemes to store solar power throughout the day and use it throughout the night, but I question whether those schemes save any money or make any more sense than just developing the space nuclear reactors that we need because no such scheme will be straightforward.”
The day before the hearing, Griffin sent Congress an updated 2005 operating plan that cuts the $430 million budget for Promethe-us by $161 million but provides no details about the restructured program other than its new priorities.
Griffin declined to go into detail about how Prometheus would be managed and how much NASA intends to spend on the program in the years ahead. He said such programmatic decisions would be driven by a broad-based exploration systems architecture study he initiated in late April and put under the leadership of Doug Stanley, a recent NASA hire who, like Griffin himself, used to work on advanced programs at Dulles, Va.-based spacecraft builder Orbital Sciences Corp. The Stanley team is expected to report back to Griffin by mid-July with recommendations on an overall approach, or architecture, for exploring the Moon and what technologies will be required and when.
Louis Friedman, executive director of the Pasadena, Calif.-based Planetary Society, applauded Griffin’s decision to refocus Prometheus on NASA’s near-term space-exploration priorities.
“The need for adequate power on the surface of planets to conduct operations cannot be overstated,” Friedman said.
Still, Friedman said he would caution NASA to ensure that its nuclear systems program is driven by what it needs for human missions to Mars, not for permanent lunar outposts. Otherwise, he said, NASA runs the risk of the Moon becoming a “terrible detour ” rather than a stepping stone on the way to Mars and beyond.
John F. Ahearne, the Duke University engineering professor and former chairman of the U.S. Nuclear Regulatory Commission who co-chaired NASA’s recently disbanded Nuclear Systems Strategic Roadmap Committee, said any reactor NASA would need for surface-power generation would require a substantial development effort.
At the final public meeting|of the roadmap committee, Ahearne’s long time colleague, Earl Wahlquist, associate director of the U.S. Energy Department’s Space and Defense Power Systems office, pointed out that the United States spent more than $500 million on its last effort to develop a space-based nuclear reactor and still had about $500 million to $600 million left to spend when the program, Space Power-100, was canceled.
Wahlquist said that reviving that program and completing it would cost on the order of $1 billion.
NASA began pursuing the development of a nuclear rocket in the late 1950s but pulled the plug in 1971, when it became clear that human missions to Mars weren’t in the agency’s immediate future.
Ahearne said NASA could develop a reactor for surface-power generation and nuclear thermal rockets concurrently, but cautioned that that might not be the most efficient path. He also said it is unlikely that NASA will embark on anything close to a crash effort to develop a nuclear thermal propulsion system for Mars excursions.
“Nuclear propulsion can offer shorter time to and back from Mars, but that is decades away and many concepts will be proposed along the way,” Ahearne said.