Two years ago on January 28, the space shuttle Challenger exploded seventy-three seconds after liftoff. Despite that disaster, however, and despite continuing problems with the shuttle booster rockets, the National Aeronautics and Space Administration plans to launch two space shuttles, one in 1989 and another in 1990, each carrying a space probe utilizing what scientists have called the most toxic substance in the universe: plutonium. Each will contain more than enough plutonium to kill every person on Earth.
Theoretically, one pound of plutonium, uniformly distributed -- a few millionths of a gram ending up in each person's lungs -- has the potential to give everyone on the planet a fatal case of lung cancer. The 1989 space probe, Project Galileo, is to contain 49.25 pounds of plutonium dioxide, most of that plutonium 238, its most radioactive isotope. The 1990 space probe, Project Ulysses, is to contain 24.2 pounds of plutonium dioxide, also mostly plutonium 238. If those amounts of plutonium were dispersed in a Challenger-type explosion, according to Michio Kaku, professor of nuclear physics at the City University of New York, there could be a "catastrophic incident" with a death toll in the thousands or tens of thousands. "It would be tragic if in the exploration of space we pollute the Earth as a byproduct. I think this is precisely what is happening here."
Plutonium 238 is 300 times more radioactive than plutonium 239, the radioisotope used as the fuel for atomic bombs, points out Dr. John Gofman, professor emeritus of medical physics at the University of California, Berkeley, and a former associate director of the Lawrence Livermore National Laboratory. "If the plutonium [from Project Galileo] gets dispersed in fine pieces, the amount of radioactivity released would be more than the combined plutonimn radioactivity returned to Earth in the fallout from all the nuclear weapons testing of the United States, the Soviet Union and the United Kingdom," which he estimates would cause 950,000 lung cancer deaths. "If it gets dispersed over Florida, kiss Florida goodbye. If it gets dispersed over Georgia, kiss Georgia goodbye."
Some scientists, chiefly from the national nuclear laboratory system and the nuclear industry, concede that plutonium is toxic but say its connection to cancer and to death in humans has yet to be proved. "The inhalation of plutonium particles can be a nontoxic, innocuous event," insists Waldo Cohn, a retired Oak Ridge National Laboratory biochemist. In reply, critics of nuclear technology point to experiments in which minute amounts of plutonium have caused death in test animals.
NASA downplays the possibility of the release of plutonium in an accident, stressing that the substance will be encapsulated in "clads" made of an alloy of iridium. "Clads were shown to survive pressure in excess of 2,000 psi [pounds per square inch],'' NASA says in an environmental impact statement for the Galileo and Ulysses missions issued in November 1987. However, a Department of Energy safety analysis report for the missions, which I obtained in 1985 under the freedom of Information Act, declared that "from the viewpoint of potential nuclear fuel release" on either of the missions, the "most critical" accidents would occur on the launch pad -- and than could generate pressures higher than 2,000 pounds per square inch. Indeed, pressure up to ten times higher were estimated. According to the report, "Because of the large quantities of liquid propellants involved and the proximity of the nuclear payload, most launch pad accidents result in explosions of a magnitude that are very severe in terms of their effect on the nuclear payload." The report details various accident scenarios, including one called a "tipover" and another a "pushover," and conludes that in either accident, there could be pressures as high as 19,600 pounds per square inch. (NASA now (1988) holds that this figure is no longer valid; the November 1987 report refers to "improved estimates of explosion parameters.")
If the space probes make it safely off the launch pad and into outer space, there are other dangers. The Project Galileo space probe will leave the space shuttle after it attains orbit to explore Jupiter. But under a new NASA plan, the probe will not be sent directly to Jupiter. In the wake of the Challenger disaster, astronauts insisted on the elimination of the highly volatile liquid-fueled Centaur rocket, which originally was to power the space probes. A solid-fuel rocket was substituted, but it does not have the power of the Centaur. So NASA devised a scheme in which the probe would first go to Venus and then be "slingshot" back toward Earth, which it would circle twice, making use of the Earth's gravitational field to increase the vehicle's momentum so it can reach Jupiter. In this second part of the sling-shot maneuver, the space probe would become a large bomb pointed almost at Earth-flying as close as 277 miles overhead. The November 1987 NASA report conceded:
The chance of a shuttle crash -- which turned out to be 1 in 25 -- was set by NASA, before the Challenger disaster, at 1 in 100,000. Another section of this report says that "operational procedures will be developed to minimize the possibility of inadvertent Earth reentry occurring during Earth return-flybys."
Why use plutonium on the space probes at all? It will not be used for propulsion. It will fuel what the D.O.E. and NASA call "radioisotope thermoelectric generators, " which supply on-board electric power, and, in Project Galileo, less than a pound will also be distributed to 130 "radioisotope heater units" to keep instrumentation warm. The D.O.E. and NASA say there are no alternatives. Professor Kaku challenges this claim and urges the use of long-lived batteries and solar energy. Even as far away as Jupiter, he says, "it's possible with the latest advances in solar cells to generate electricity" from the sun. And for Project Ulysses, whose mission is a north-south orbit of the sun, there is certainly plentiful solar energy.
Project Galileo was originally scheduled for launch four months after the Challenger mission, and Project Ulysses was to follow weeks later -- indeed, it was to be the next mission of the ill-fated Challenger. Last year I queried the D.O.E. and NASA about what new safety analyses they had made for the two projects since the Challenger disaster. The reply from D.O.E., which provides the plutonium-fueled electric generator and heat source (both made by Genaal Electric) to NASA, was: "Since that time, no further studies/reports have been completed on this subject."
Reprinted online by permission of the author.