Cosmos 1402's uranium remains.

Cosmos 1402's uranium remains

When a Soviet satellite called Cosmos 1402 was launched into orbit around the earth on Aug. 30, 1982, it carried a nuclear reactor containing up to 50 kilograms of uranium-235. After the satellite had finished its job, the reactor--used to power an ocean-reconnaissance radar system-- was supposed to be separated from it and boosted to a higher orbit, where its radioactive core would presumably stay aloft for centuries. However, a malfunction prevented the orbit from being raised, and on Feb. 7, 1983, the reactor reentered the atmosphere.

But what happened to it then? The consensus was that the device had burned up from atmospheric friction high above the South Atlantic Ocean. This would have reduced its radioactive heart to dust-like particles that would circle on the winds for months or years before settling out, rather than coming down as solid pieces of debris. But at the time, according to a group of U.S. researchers whose report appears in the Oct. 23 SCIENCE, "there was no direct evidence that this occurred.'

Both scenarios have occurred before and both have the potential for being harmful. Heavier chunks represent greater concentrations of radioactivity, while fine particles can cover far more terrain by the time they finally do fall, depending on the winds, the altitude of burn-up and other factors.

Now the scientists' analysis, based on samples collected in paper filters by highaltitude balloons before and after the satellite's reentry, has indicated that most or all of the reactor's uranium-235 "dust' was indeed still present in the upper atmosphere more than a year later.

The technique involved using mass spectrometry to measure variations in the exposed filters' relative amounts of uranium-235 and -238, both of which exist in tiny amounts in the atmosphere and even in the unexposed filter paper. The uranium-238 showed similar concentrations in the samples from both before and after Cosmos 1402's reentry, as well as in several unused filters, according to Robert Leifer of the Department of Energy's Environmental Measurements Laboratory in New York City, together with colleagues from that lab and from the National Measurements Laboratory of the National Bureau of Standards in Gaithersburg, Md. A clearly measurable excess of uranium-235 was found, however, in one of the three post-reentry filters.

The timing of the balloon launches to give them the best chance of detecting radioactive fallout from Cosmos 1402 was based on measurements that had been made after the 1964 reentry of a plutonium-powered system called SNAP-9A aboard a U.S. satellite that had failed to get into orbit. A particularly widely reported reentry was that of the Soviet Cosmos 954 satellite in 1978, which deposited radioactive debris over a large area of northwestern Canada.

One concern that has been raised about the possible reentry of satellite nuclear materials is that of contamination by more toxic fission products such as strontium-90 or cesium-137. In Cosmos 1402's case, notes Leifer, "we could not detect any fission products in the samples.' On the other hand, says Steven After good of the Los Angeles-based Committee to Bridge the Gap, the administration's Strategic Defense Initiative is funding the development of much higherpowered space-borne reactors, "despite President Reagan's pledge that [SDI] would offer a non-nuclear defense.'