WASHINGTON — NASA has released for public comment a draft environmental impact statement on the proposed launch of the nuclear-powered New Horizons Pluto mission. NASA plans to launch the spacecraft in January or February 2006 from Cape Canaveral Air Force Station, Fla. aboard an Atlas 5 rocket.

The New Horizons probe is equipped with a radioisotope thermoelectric generator (RTG) that transforms heat from decaying plutonium-238 into electricity to power the spacecraft’s science instruments and other electronics.

Under the National Environmental Policy Act of 1969, NASA is required to prepare an environmental impact statement for all launches and make it available for public review.

Kurt Lindstrom, the New Horizons program executive at NASA Headquarters here, said that after the 45-day public comment period ends April 11, he and other program officials will develop a final environmental impact statement that they will forward around August to Al Diaz, NASA’s associate administrator for science, and request that he sign off on an official record of decision to launch the nuclear-powered spacecraft.

Lindstrom said development of the New Horizons spacecraft remains on track and on schedule for its planned launch.

The U.S. Department of Energy’s Los Alamos National Laboratory, which fell behind schedule last year preparing the plutonium needed for the mission, has since delivered the required quantities to the Idaho National Laboratory, which will prepare a fueled RTG in time to ship it to Cape Canaveral this fall for integration with the spacecraft.

Lindstrom also said that the probe’s main detector package, dubbed Ralph, is due to be delivered this month to Johns Hopkins University’s Applied Physics Laboratory, the Laurel, Md.-based lab that is building the New Horizon’s spacecraft for NASA and the Southwest Research Institute, Boulder, Colo.

Ralph was supposed to be finished and sent on to APL late last year, but Lindstrom said the contractor building it, Boulder-based Ball Aerospace & Technology, ran into schedule conflicts and had to put the project on the back burner temporarily to work on higher priority projects. He said the delays were “not really a technical problem” but due to “scheduled conflicts with other programs at Ball.”

Ball spokesman David Beachley, however, said the “delays were primarily due to technical challenges” and the complexity of orchestrating the various partners involved in designing and building the instrument suite. Beachley said a new schedule was agreed to Oct. 1 and that the development effort has remained on track since then. He said Ralph is currently undergoing environmental testing and will be delivered by the end of March as required.

Lindstrom said the delay has added about $6 million to the cost of the program, which is expected to cost about $650 million through the spacecraft’s 2015 or 2016 encounter with Pluto.

Although New Horizons may not launch with as much on-board power next year as originally hoped, Lindstrom said Department of Energy came through with enough plutonium to keep open the possibility for New Horizons to visit one of Pluto’s Kuiper Belt neighbors after the fly by.

If the mission goes as planned, he said, New Horizons should have enough power to go an additional three years and reach the Kuiper Belt. NASA has yet to agree to fund such an extended tour, and probably will not make a decision one way or another before 2013, he said.

Before NASA can even launch New Horizons, however, it also needs White House approval, either from the president himself or his designate in the Office of Science and Technology Policy. Lindstrom said NASA is working that launch approval process in parallel with the environmental impact process.

The RTG that NASA is using on the New Horizons spacecraft is built to survive the heat of re-entry intact. In the event of a launch mishap that fails to put the satellite in orbit, Lindstrom said the RTG would break apart from the spacecraft and fall back to Earth — most likely into the ocean given the launch trajectory out of the Cape — without releasing plutonium. In such a scenario, Lindstrom said, a ship could be dispatched to recover the RTG, something the United States has done at least once in the past, such as in 1968 when an Atlas Agena rocket carrying a NASA-built Nimbus-2 weather satellite went off trajectory and had to be destroyed. Several months later, they fished the undamaged RTG out of the Pacific Ocean. Lindstrom said the recovered plutonium was later reprocessed.

RTGs have also been left in the ocean, as was the case in 1970 when the Apollo 13 mission had to be aborted on its way to the Moon. The Lunar Excursion Module burned up as it re-entered Earth’s atmosphere, but its RTG survived the freefall into the depths of the Pacific Ocean. No radiation was released, according to NASA and the Department of Energy.

Lindstrom said the New Horizons RTG contains approximately 10 kilograms of plutonium pellets housed in 18 separate modules tough enough to survive both the trauma of a rocket that self destructs and the extreme heat of atmospheric re-entry.

The plutonium used in RTGs is not suitable for nuclear weapons, nor is it radioactive in the popular sense of the word. Because Plutonium-238 emits only alpha rays, which are incapable of penetrating human skin, the material has to be inhaled to cause harm.

Lindstrom said the biggest safety concern about launching an RTG-equipped payload is the risk of a near pad accident, such as the rocket exploding before clearing the launch area or otherwise failing before it is out over water.

“The real area of concern is the first 40 seconds of flight, the first 25 of which the rocket is still over land,” Lindstrom said. “After that, if the flight termination system is activated [before the end of 40 seconds], there is still the possibility of debris landing on land.”

Though such near-pad accidents are rare compared to higher altitude launch vehicle failures, Lindstrom said they pose the greatest danger of a plutonium release because the RTG’s plutonium modules could crack open if they hit a hard enough surface. In most such cases, Lindstrom said, the environmental contamination would be limited to the immediate vicinity of the damaged plutonium modules and relatively easy to contain. A very unlikely but more troubling scenario involves a rocket blowing up on the pad, with a cracked RTG engulfed in fire which would help spread plutonium into the atmosphere, exposing people living in the surrounding areas to greater long-term risk of cancer.

NASA’s risk assessment, according to the draft environmental impact statement, calculated the odds of such catastrophic failures as no greater than 1 in 1.4 million and perhaps even lower than 1 in 12 million.

The Department of Energy prepared the risk assessment with the help of the Department of Energy.

The United States has launched about two-dozen RTG-equipped spacecraft since the 1960s, with only three known mishaps, none of which were related to the RTG itself. Besides the Nimbus 2 and Apollo 13 mishaps, the United States lost a Transit navigation satellite in 1963 that was equipped with an early RTG designed to burn up upon re-entry. When the satellite was dropped short of its intended orbit and re-entered, the SNAP 9-A RTG burned up, disbursing roughly 3 kilograms of plutonium particles into the atmosphere.

Russia has had at least five spacecraft mishaps involving RTGs, the worst believed to be the 1977 Kosmos accident that scattered radioactive particles over parts of Canada when the spacecraft broke up upon re-entry. Russia also lost a Mars-bound mission in 1996 that re-entered and broke up over South America.

NASA’s most recent launch of an RTG-equipped spacecraft occurred in 1997, when an Atlas 4 rocket lofted the Saturn-bound Cassini-Huygens spacecraft into orbit.

Cassini’s launch met with protests from anti-nuclear activists concerned about the danger of launching a spacecraft with three RTGs that was designed to swing back past Earth on its way out to Saturn.

One of those protesters was Bruce Gagnon, co-coordinator of the Global Network Against Weapons and Nuclear Power in Space. Gagnon said he plans to do what he can to stop the New Horizons launch.

“We oppose all of these nuclear launches, every single one of them and we will be organizing to oppose this one as well,” he said.

Gagnon said he and other activists will put their concerns about the launch on the record during the public comment period and have not ruled out taking legal action to keep New Horizons from going forward. But he said he does not think anything he or anyone else has to say has much of a chance of stopping the launch.

“They are going to go ahead,” he said. “They don’t give a damn about public opinion. NASA is controlled by two entities today, the Pentagon and the nuclear industry. NASA just doesn’t give a damn about the public’s input.”

The public has until April 11 to comment on the draft environmental impact statement, which is posted on the internet and available for viewing at NASA Headquarters and the space agency’s 10 regional field centers in addition to the Applied Physics Laboratory.

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...