THE United States' decision to buy an advanced version of the nuclear reactor the Soviet Union uses to power spy satellites represents a mixed blessing. Soviet willingness to sell such sensitive technology is yet another welcome sign of a new era in Soviet-American relations, as well as a concession to the Soviets' need for hard cash. It also is a useful opportunity for US engineers to learn more about technology - especially high-tech materials - in which Soviet experts excel.
At the same time, the sale renews concern about use of reactors in space. A number of dead Soviet reactors already circle our planet, each loaded with extremely dangerous radioactive fission products. They are in nominally safe orbits and unlikely to crash to Earth, as did one spent reactor whose booster failed to push it into a parking orbit. Nevertheless, they are a nasty kind of space debris.
Nuclear propulsion may be appropriate for missions well away from Earth. It can be both powerful and efficient. But it should not be used in near-Earth orbits, as scientific groups in both the US and the Soviet Union have repeatedly stated.
The Soviet reactor is being imported for study, not for use in space. Its experimental use will be part of the ongoing research on nuclear space propulsion carried on by the Departments of Energy and Defense. The National Aeronautics and Space Administration, which has just reestablished its Office for Nuclear Propulsion, is also interested.
That seems fine, as far as research goes. But the Soviets have already tested the new reactor in space and continue to use reactor power sources on satellites. The United States should work harder to convince the Soviets to abandon this dangerous use of space nuclear power even while it studies the latest relevant Soviet technology with fascination.