Nuclear

By Anastasia Toufexis

If the shuttle Atlantis lifts off this week from its Cape Canaveral launch pad as planned, astronomers will let out a long-delayed cheer. At last the Galileo mission, which has languished for more than a decade because of technical debates and the Challenger explosion, will be getting under way. Astronauts on Atlantis will release the Galileo spacecraft, setting it on a six-year, 2.5 billion-mile journey to Jupiter. There the probe will take the first direct measurements of the planet's dense clouds and hurricane-like winds.

Few doubt the scientific value of the Galileo flight. Nonetheless, a sharp controversy has dogged the mission. At issue is the space probe's power source: two radioisotope thermoelectric generators that are fueled by almost 50 lbs. of highly radioactive plutonium 238. Antinuclear groups, led by the Florida Coalition for Peace and Justice and the Washington-based Christic Institute, have claimed that the generators are unsafe. Their view is shared by Richard Cuddihy, an analyst with the Inhalation Toxicology Research Center in Albuquerque and the lone dissenter on the federal interagency panel that recommended a go-ahead for the Galileo program. Says Cuddihy: "The risks of the launch are greater than those originally estimated by the committee."

Opponents charge that a disaster during launch could spew large amounts of radioactive fallout throughout Florida and cause 2,000 cases of lung, bone and liver cancer. The danger, they say, does not end with a successful takeoff. To gather momentum, the Galileo spacecraft will first make a swing around Venus and two around the earth before hurtling off to Jupiter. Critics are concerned that the vehicle could collide with the earth during close flybys in 1990 and 1992.

NASA used similar generators on 22 space missions, but no one paid much attention until the Challenger tragedy dramatized the risks of space launches. The space agency admits that there have been three accidents involving RTG- powered vehicles. The most significant was in 1964, when a satellite launched by the Air Force burned up over the Pacific, tripling the amount of radioactive plutonium 238 in the environment. It is not clear what health effects that might have had. The generators were then redesigned, and in two subsequent accidents in which spacecraft broke apart, no radioactivity is known to have escaped.

NASA has gone to extraordinary lengths to make sure the RTGs are safe. Each of the 144 plutonium pellets in the generators, designed by General Electric, is surrounded by an iridium shell. Coated pellets are then encased by two graphite shells and finally by an aluminum shroud. The U.S. Department of Energy has spent $50 million testing the generators. In one experiment, engineers fired shrapnel traveling 700 ft. per sec. at the iridium casings. None was pierced. In another test, scientists tacked an RTG to a solid rocket booster and blew it up. No damaged graphite shells were detected.

Space officials calculate that the chances of plutonium being released in an aborted mission are no greater than 1 in 1,428. Declares Dudley McConnell, nuclear safety manager for NASA: "You have a thousand times greater chance of dying on the ground from debris falling from an airplane crash than you do from the Galileo mission." Critics, though, remain unconvinced by such assurances. For them, the only real comfort will come when Galileo is gone from earth.

With reporting by Glenn Garelik/Washington and Sue Butler Hannifin/Cape Canaveral