More than eight years ago, hundreds of protesters chanted anti-nuclear slogans before NASA launched a spacecraft to Saturn carrying 72 pounds of plutonium fuel. The noise before this week's launch of a craft with a similar payload has been more muted.
Only 30 anti-nuclear protesters showed up recently to oppose a plutonium-fueled mission to Pluto. The most raucous it got was when protesters tied colorful origami birds to the fence of the Cape Canaveral Air Force Station.
"Folks tend to forget," said protest organizer Maria Telesca of the Global Network Against Weapons & Nuclear Power in Space.
But Telesca and other protesters said the threat of a nuclear accident is no less real with the New Horizons mission to Pluto than it was with the launch of the Cassini probe to Saturn in 1997.
Plutonium fuel has been used on two other spacecrafts taking off from the Cape Canaveral area since Cassini's launch. The two Mars rovers, Spirit and Opportunity, sent up in 2003, had much smaller amounts of plutonium, which creates energy from natural radioactive decay.
Twenty-four pounds of radioactive plutonium is located in New Horizon's radioisotope thermoelectric generator, an aluminum-encased, 123-pound cylinder, 3½ feet long and 1½ foot wide, that sticks out of the spacecraft like a gun on a tank.
Inside the cylinder are 18 graphite-enclosed compartments, each holding 1 1/3 pounds of the plutonium dioxide. Similar generators previously have been used to power six Apollo flights and 19 other U.S. space missions.
NASA and the U.S. Department of Energy have put the probability of an early-launch accident that would cause plutonium to be released at 1 in 350 chances.
NASA last year estimated the cost of decontamination, should there be a serious accident with plutonium released during the launch, at anywhere from $241 million to $1.3 billion per square mile, depending on the size of the area.
If there was an accident during an early phase of the launch, the maximum mean radiation dose received by an individual within 62 miles of the launch site would be about 80 percent of the amount each U.S. resident receives annually from natural background radiation, according to NASA's environmental impact statement.
The space agency is setting up two radiological control centers and deploying 16 mobile field teams that can detect radiation around the launch site. Medical personnel at local hospitals also have been trained in the treatment of patients exposed to radioactive materials, and the launch required the approval of the White House.
The emergency plans are ready for Tuesday, "if need be, but hopefully not," NASA launch director Omar Baez said Sunday at a news conference.
Some NASA safety managers had raised concerns about the New Horizons mission when a fuel tank similar to the one expected to be used failed a pressure test during factory evaluation.
The original launch date was pushed back a few days to allow more time to examine the flight tank, but the decision ultimately was made to fly since the flight tank was in pristine condition and had no signs of any defects, Baez said.
Even if plutonium were released during an accident at launch, the risk to the population would be low because of the small amount of nuclear material and the remoteness of the launch pad from populated areas, said Alice Caponiti, nuclear material and safety manager at the Department of Energy's Office of Space and Defense Power Systems.
"Once you get a probability of an accident occurring, the question is what's the impact to people?" Caponiti said. "That's where the risk is low."