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NASA Goes Nuclear

When your batteries are dead and solar power is only a distant memory, you're going to need something else in your power pack.

OFFICIALS AT NASA HEADQUARTERS IN WASHINGTON, D.C., WERE BATTING AROUND names for their soon-to-be-announced nuclear program last fall when Administrator Sean O’Keefe offered a suggestion. Why not call it Project Prometheus, after the giant in Greek mythology? It was Prometheus, after all, who brought fire, and with it civilization, to humankind. So far so good. But the story has a disturbing end. For Prometheus’ effrontery, Zeus had him chained to a rock, helpless to defend himself as an eagle pecked out his liver, over and over, day after day.

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“We had several rounds of e-mails with the Administrator over whose liver was going to be pecked out,” jokes Al Newhouse, a former Navy nuclear engineer who heads Project Prometheus at NASA headquarters. “That was funny, except it was always mine.”

After decades of false starts and dashed hopes, Prometheus marks the return of nuclear reactor development for U.S. spaceflight. In June 1993, after 10 years of work, Congress voted to end the last space reactor project, called SP-100, before it even got to the point of ground testing. Newhouse remembers the day well. He had moved over from the Navy to join the Department of Energy as SP-100 director. “I was put in the position of shutting down the program that I was brought in to nurture and support,” he says.

Now O’Keefe, a former Secretary of the Navy who is familiar with nuclear-powered submarines and aircraft carriers—and whose father was a nuclear sub engineer—has recruited Newhouse and other Navy veterans with nuclear expertise to run Prometheus, which will produce advanced systems for both power and propulsion.

This time Newhouse hopes things will be different. The trouble with SP-100, he says, was that it never had a guaranteed customer. While the reactor was in development, both of its intended users—Ronald Reagan’s “Star Wars” space weapons program and the (short-lived) proposal of his successor, George Bush, to send astronauts to the moon and Mars—fell by the wayside. This time, though, NASA has asked the energy department to build a reactor for a specific purpose—to power a robotic mission to explore three moons of Jupiter as early as 2011. After that, it will provide electricity for future planetary spacecraft far more capable than past Vikings and Voyagers, which used either solar power or small plutonium batteries.

Prometheus is a gamble, both technically and politically—because launching radioactive material is likely to generate protests and create a public relations problem for NASA. But many people, O’Keefe foremost among them, believe nuclear power is the only way for NASA to take the next step in space exploration. Agency science chief Edward Weiler recently told a committee of the National Research Council that O’Keefe “not only calls it the future of planetary exploration, he calls it the future of NASA.”

If you compare the proposed Jupiter Icy Moons Orbiter (JIMO) to the Cassini spacecraft now headed for a July 2004 rendezvous with Saturn, it’s easy to see what he means. Cassini’s electricity comes from radioisotope thermoelectric generators, which have been standard equipment on spacecraft venturing too far from the sun to rely on solar power. The RTGs on Cassini produce power from the decay of plutonium and generate about 900 watts, enough electricity to power nine standard light bulbs. JIMO’s nuclear reactor will produce 100 kilowatts, or several times the average daily household use.

For planetary exploration, that kind of power output is revolutionary. It means data will come back to Earth in unprecedented volumes—120 CD-ROMs’ worth for the entire mission, compared to a couple of floppy disks for Cassini. Instead of observing Jupiter’s moon Europa for a few hours at close range, which had been the plan for a non-nuclear mission NASA was considering as recently as last year, JIMO will study three Jovian moons for a total of 180 days. And it can carry a much more powerful sounding radar to probe for an ocean suspected to lie beneath Europa’s icy crust.

First, though, Prometheus has to deliver the fire. On a conceptual level, a space nuclear reactor would work much like a reactor on the ground. Neutrons given off by a radioactive fuel, in this case uranium, would strike other uranium atoms, which would then split to create more neutrons, perpetuating the reaction and generating heat, which would be absorbed by a coolant and converted to electricity.

But most nuclear reactors aren’t launched on rockets from the densely populated Florida coast. So Department of Energy engineers will have to assure critics that in the event of a launch accident, a space reactor won’t suddenly start splitting atoms. “Safety becomes the driver in the reactor design,” says Earl Wahlquist, head of DOE’s Office of Space and Defense Power Systems in Maryland.

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