16 January 2006
There are two ways of looking at NASA's New Horizons launch on Tuesday.
It's the first mission to a new frontier - Pluto and beyond - and a chance to fill in the missing link in the 46-year reconnaissance of our solar system.
Or it's 24 pounds of plutonium perched atop 2.5-million pounds of thrust with a 1 in 350 chance of blowing up.
Mary Telesca doesn't like those numbers.
The rocket is on a Kennedy Space Center launch pad 20 miles from Telesca's Rockledge home. She plans to be far away at launch time.
"My family always evacuates," said Telesca, a homeschool mom and a regular at protests of nuclear-powered spacecraft on Florida's Space Coast. "People tease me about it, but they are the same people who evacuate for a hurricane."
But she's in a distinct minority.
Opponents say Sept. 11, 2001, and the Iraq war have distracted the country's attention.
"People are getting kind of burned out on demonstrations," Telesca said.
Like it or not, nuclear power and NASA are inextricably linked.
"I think if humans are really going to explore the solar system, or go beyond our immediate neighborhood, we are going to have to go with nuclear power," said Steve Howe, director of the Center for Space Nuclear Research at the Idaho National Laboratory. "Nuclear power really is the development of the steam ship compared to sailing ships."
NASA insists New Horizons is safe.
The agency says the odds of someone in Florida getting cancer from an accident at launch range are 1 in 1.4-million to 1 in 18-million. Statisticians put similar odds on dying in a bathtub (1 in a million) or getting killed by lightning or a tornado (both 1 in 2-million).
Cleanup costs in those scenarios range from $93-million to $1.3-billion per square mile. The potential area for a launch accident extends 62 miles around the space center.
The $700-million space probe is powered by a radioisotope thermoelectric generator, or RTG. RTGs convert radioactive heat from the decay of plutonium-238 into electricity.
At Pluto, New Horizons will be able to squeeze out about 20 0 watts of electricity - equivalent to a couple of light bulbs - to power its science instruments.
RTGs have flown safely on 24 NASA missions since 1961, including six Apollo journeys and every spacecraft sent beyond Mars. RTGs have kept NASA's twin Voyager spacecraft functioning more than 8-billion miles from the sun.
The crash of a Russian Mars probe in 1996 sparked protests when Cassini launched in 1997 with a record 72 pounds of plutonium for its exploration of Saturn. It launched safely.
Without its three RTGs, Cassini would have needed solar panels the size of tennis courts.
"The only technology we have for these deep outer planet missions are these RTGs, which have been used since I was a kid," said Alan Stern, 48, the lead scientist on the New Horizons mission. "You can't use solar panels out there. If we couldn't fly an RTG, we couldn't fly this mission or anything like it."
Plutonium-238 can't be used to make nuclear weapons. It won't melt down like a nuclear reactor.
The plutonium is in ceramic pellets that can't easily shatter into plutonium dioxide dust, which can cause cancer if inhaled. The pellets are encased in a container designed to survive re-entry.
The RTG is the workhorse of deep space exploration. Engineers also use radioactive material to keep rovers warm. NASA's Mars Exploration Rovers, in their second year on Mars, would have frozen long ago without their radioisotope heater units.
About 10 nuclear-powered spacecraft have crashed worldwide, though Soviet secrecy makes specific numbers hard to get. Most accidents involved Soviet spacecraft. A few spread dangerous radioactive dust across the planet, but no direct health effects have been documented from nuclear spacecraft accidents.
"Space technology can and does fail," said Bruce Gagnon, coordinator of the Global Network Against Weapons and Nuclear Power in Space. "When you mix plutonium into the equation, we think you're asking for trouble. It's not theoretical. It's real."
Cassini was the last big spacecraft that needed nuclear power, but last year NASA once again embraced nuclear power for space exploration. The agency announced ambitious plans to send a reactor-powered spacecraft to search for oceans under the icy crusts of Jupiter's moons.
That mission was scrapped when NASA's priorities shifted to replacing the space shuttle. But NASA hasn't given up on expanding its nuclear research. It plans to spend $319-million this year, and twice that by 2010.
"We're in a reformation period with our nuclear program," said Carl Walz, a NASA nuclear systems expert. "Potentially, nuclear power is a very valuable power source."
Gagnon sees a sinister trend.
"We think these NASA missions are an icebreaker," he said. "Is it not true the Pentagon wants nuclear reactors for weapons in outer space? They are building the infrastructure to create a whole lot more of these things."
Roger Launius, chairman of the Space History Division of the Smithsonian Air and Space Museum, said anything beyond RTGs may be a hard sell.
"There obviously are people who want to pursue reactor power," he said. "That's more problematic from a safety standpoint. When you create a reactor that splits atoms and that sort of thing, you're creating a more volatile system than an RTG."
Howe of Idaho National Laboratory said reactor power is safe because the fission reaction can be started far from Earth. He said nuclear power could make life easier for moon and Mars colonists and also shorten trips between the planets. It might shave an astronaut's year and a half stay on Mars to two months.
"In my opinion, a nuclear rocket is an enabling technology for humans to go to Mars," Howe said.
Telesca doesn't think much of the need or the assurances of safety. "We bought some land in the mountains of Virginia," she said. "We are planning to relocate to that area in the next few years."
Gagnon said nuclear power advocates ignore alternatives. For example, the European Space Agency's comet-chasing Rosetta spacecraft set distance records using enhanced solar panels.
"Pluto has been there a long time," he said. "If we had to wait a little longer to do it right, what would be the harm?"
New Horizons scientist Richard Binzel says there's less time than Gagnon thinks. Pluto is moving away from the sun in a wide arc. In the next decade or so the planet's atmosphere could freeze and collapse on the surface. A later arrival means more of the planet's polar regions will plunge into 124 years of darkness.
"Getting there sooner is better than later," said Binzel, a professor of planetary science at MIT. "We're losing real estate the longer it takes to get there."