Anti-nuclear activists are pleased the plans to send a deep-space probe to explore Pluto have been shelved for now. 

To their horror, though, the Pluto-Kuiper Express has been sent back to the drawing board for the "wrong" reason — cost instead of safety. But the activists are lucky the mission's cost is so high. Their alleged safety concerns won't make it off the launch pad. 

Anti-nuclear activists allegedly are concerned about the plutonium used to power the space craft. In the event of a launch accident, they claim, the plutonium could be vaporized, resulting in dangerously high local radiation exposures. A late-launch accident would result in global dispersion of plutonium particles, according to the activists. 

This is not the first time the activists have spread fear in hopes of trying to stop a plutonium-powered space launch. 

In October 1997, the National Aeronautics and Space Administration launched the Cassini space probe to Saturn. Cassini's power source for its 11-years-or-more mission was 73 pounds of plutonium. 

As the radioactive plutonium decays, it gives off heat, which is converted into electricity by three so-called radioisotope thermoelectric generators. RTG power systems have been used by NASA more than 20 times in the past 30 years. Three missions ended in accident without dispersion of the plutonium. 

NASA acknowledged that under a worst-case scenario, a Cassini launch accident could result in billions of people exposed to low levels of radiation, equivalent to the radiation exposure from a 40th of a dental X-ray. 

The agency estimated such radiation exposure might result in an "extra" 120 to 2,300 deaths from lung cancer over the next 50 years. An independent analysis led by the Massachusetts Institute of Technology estimated the odds of the worst-case scenario occurring to be one in a million.

The activists chose to rely on the estimate of a death toll between 30 million to 40 million from University of Pittsburgh professor Ernest Sternglass, who is also a director of the Tooth Fairy Project — the Alec Baldwin- and Christie Brinkley-endorsed effort to measure levels of Strontium-90 in baby teeth and blame nuclear power and weapons facilities for an alleged "cancer epidemic." 

Despite the activists' best efforts at fearmongering, the Cassini launch went ahead as scheduled. 

Another fearmongering opportunity occurred in August 1999 as Cassini made a scheduled pass 727 miles from Earth. Michio Kaku, a physics professor at City College of New York and Cassini opponent, said, "One paint fleck could just blow Cassini apart and send it spiraling to Earth." 

But NASA claimed the chance that Cassini would hit a piece of junk larger than a gram was one-in-13 million. Sure enough, Cassini passed by without incident on its way to Saturn. 

The flash point for the anti-nuclear activists is plutonium-238, a heat-resistant, highly insoluble ceramic form of plutonium — not what's used in nuclear weapons or power plants. The concern over plutonium is emission of alpha particles that, if inhaled, can damage DNA. But plutonium-238 breaks mainly into large chunks that can't be inhaled. Very little dust would be produced, according to NASA. 

"[Plutonium] would have to get into the air as very, very fine particles that could be inhaled to be a problem," says plutonium expert Bernard Cohen, a physicist at the University of Pittsburgh. "Even if [Cassini] reentered the atmosphere, there won't be any epidemics. You'd never see the effects and you'd never detect anything. This business of a single particle [of plutonium] that can kill you is nonsense. The demonization of plutonium is very unscientific." 

Anti-nuclear activists say the electricity needed for the Pluto-Kuiper Express could be generated with fuel cells or other unnamed technologies. But the European Space Agency estimates it would take two solar panels, each bigger than two tennis courts, to replace the RTGs. 

The activists' other alternative is to scrap the mission to Pluto altogether, remarking, "99.999999999 percent of the solar system has yet to be explored at all, so there are lots of choices." 

NASA halted the PKE program because costs increased from $350 million to $500 million just in the past year. Because of the delay, a spacecraft now is not expected to reach Pluto until 2020, which may be too late. Pluto's atmosphere is starting to freeze as the planet moves into a winter lasting more than 100 years. 

Anti-nuclear activists are fortunate that costs matter to society. The costs imposed through their fearmongering — not the safety issues raised — have essentially stopped the development of clean and safe nuclear power in the U.S. Of course, cost is a two-edged sword. 

One day the costs to society of anti-nuclear hysteria will be so high that the "no nukes" crowd may find themselves on their way — as Ralph Kramden would say — "to the moon!" 

— Steven Milloy is a biostatistician, lawyer, adjunct scholar at the Cato Institute and publisher of Junkscience.com.