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13 February 2002 |
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NASA plans to spend nearly$1 billion on a controversial effort to rejuvenate its nuclear power and propulsion programs, capabilities it believes are crucial to the exploration of the outer solar system and rooting out evidence of life on Mars. The space agency unveiled the five-year strategy to equip a new wave of planetary missions with nuclear components as part of the 2003 budget President Bush unveiled earlier this month. Pending congressional approval, NASA would aim to launch a nuclear-powered terrain-roving robot to Mars in 2009. Meanwhile, the agency has canceled a mission to Pluto that was tentatively slated for a 2006 launch until it can furnish nuclear propulsion and power to cut the travel time and lengthen the reconnaissance period. Proponents of the nuclear initiative claim they have no intention of constructing nuclear-reactor-fired rocket launchers or space-fission-powered generators that expel radioactive materials like those experimented with during the Cold War. The new systems would rely on heat produced by the natural decay of radioactive plutonium to generate electricity or create propulsive thrust from non-nuclear xenon fuel. Conventional chemical rockets would launch the spacecraft equipped with nuclear components. Supporters of the nuclear initiative, however, are hopeful the design breakthroughs could be scaled up eventually. More capable nuclear power and propulsion systems could be used by future human exploration of the solar system. "The bottom line is that we have reached a crossroads here. We have reached the limits of what we can do (with conventional propulsion and power)," said Ed Weiler, chief of NASA's space science division. "We are doing space exploration the way we did it 40 years ago. It's time to move forward." The space agency is seeking about $150 million for 2003 as the first installment in the $950 million it hopes to invest over the next five years. Most of the near-term funding would restart the production of plutonium-fueled radioisotope thermoelectric generators, or RTGs, by the Department of Energy. The RTGs would be used for the 2009 Mars rover mission and prospective missions to Pluto, Uranus, Neptune and Europa, the ocean-covered moon of Jupiter. For the most part, NASA and the military have relied on solar energy and temperamental fuel cells to generate electricity for their spacecraft. Neither system, however, is practical for deep space destinations, where the sunlight is too weak for solar arrays and the journey too long for fuel cells that require replenishment with volatile hydrogen and oxygen.
The United States has turned to RTGs as a power source more than two
dozen Launched in 1977, NASA's Voyager 1 and 2 probes snapped the first close-up photos of Jupiter, Saturn, Uranus and Neptune before departing the solar system. Their aging RTGs continue to generate electricity and both spacecraft still transmit findings back to Earth. The 1997 launch of NASA's Cassini to Saturn was the most recent mission to rely on RTGs. That mission left NASA with just one functional RTG, plus components for a second and some spare parts. Like other missions that relied on the plutonium-fueled generators, Cassini's launch was accompanied by protests from anti-nuclear demonstrators. Their concerns included warnings that Cassini's Titan launcher would explode at liftoff, showering the central Florida coast with cancer-causing radioactive plutonium. Supported by the findings of an environmental impact statement, NASA argued that the risk of an explosion was low and that the metal-clad plutonium pellets in the RTGs would survive an explosion intact. The statements from the space agency and environmentalists echoed those that also surrounded the 1990 and 1989 space shuttle launchings of the Ulysses and Galileo probes. Those spacecraft successfully explored the polar regions of the sun and Jupiter and, like Cassini, lifted off without creating a radiation hazard. "Somewhere along the way, our judgment is, there will be accidents," said Bruce Gagnon, the Florida-based coordinator of the Global Network Against Weapons and Nuclear Power in Space, a coalition of 150 small groups that is mobilizing opposition to the latest NASA nuclear initiative. "We see it as Russian roulette. There is a bullet in the chamber, and eventually it will come around if you keep pulling the trigger." The space agency contends it will proceed only if the technology is fail-safe "I want everyone to start with the premise that we will design systems that are absolutely as safe as possible no matter what happens on the launching pad, including an entire disaster with the launch vehicle," said Weiler. The space agency intends to assign the first of the newly produced RTGs to the 2009 launching of an unmanned Mars robotic rover. The mechanical geologist would closely examine the Red Planet's rocks and soil for evidence of past or current biological activity. Once slated for a 2007 liftoff, the space agency decided on a two-year delay so it can equip the rover with nuclear rather than solar power. It would extend the robot's life from six months to nearly three years, said Jim Garvin, NASA's chief Martian scientist. The range of the rover's travels would grow from just a few miles to nearly 60 miles. With success in 2009, NASA might incorporate nuclear power into a future Mars rover designed to drill into the planet's desertlike terrain in search of subterranean ice or water deposits that harbor signs of microbial life. For years, scientists have debated the merits of a mission to Pluto, the only planet yet to be visited by a camera-carrying spacecraft. At 2.8 billion miles away, the journey would take at least a decade with a conventional rocket. But to reach Pluto in 10 years, the probe would have to be launched by 2007. Without nuclear propulsion, the journey to Pluto would require the probe to first pass close enough to Jupiter for a gravitational sling toward its final destination. If the mission is not launched by 2007, scientists must wait 15 years until Jupiter is favorably aligned for the sling. Last year, Congress directed NASA to start a more than $500 million Pluto mission over agency objections.
NASA hopes to defer the flight until it can develop a nuclear propulsion
system capable of reaching Pluto in a decade without a boost from
Jupiter.
With nuclear electric power, the spacecraft also could orbit Pluto for
several years. Without it, the spacecraft could only fly by Pluto for
about
30 days. |
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