Ban radioactive derelicts from the space overhead

`IT'S a mysterious cosmic event! No, it's just another orbiting nuclear reactor.'' This litany has become all too familiar to astronomers who study the universe with gamma rays.

Like light and radio waves, gamma rays are a form of electromagnetic radiation. Exploding stars, violent events in the core of galaxies, and many other cosmic processes produce this highly energetic radiation. Cosmic gamma rays can't get through Earth's atmosphere. So astronomers have had to learn to use instruments on rockets and satellites to study them.

But just as the new science of gamma ray astronomy is hitting its stride, gamma-ray-emitting Soviet spy satellites are messing up the observations. Dr. Edward L. Chupp of the University of New Hampshire, for example, has said that ``the situation has become completely unlivable in the last couple of years.''

It's time the United States and the Soviet Union worked out a permanent ban on using nuclear reactors in Earth orbit.

World attention focused on this issue last summer when the reactor aboard Kosmos 1900 threatened to fall out of the sky. Two previous Soviet reactors had done just that, in 1978 and 1983.

This time, happily, spacecraft mechanisms ejected the reactor into a safe orbit before Kosmos 1900 itself reentered the atmosphere Oct. 1.

Only the Soviet Union now uses reactor-powered satellites. It has orbited at least 33 of them. Generally, the reactors they carry are left in ``graveyard'' orbits, where they will remain until their load of radioactive waste has decayed. The United States, however, is developing an advanced reactor to power both military and civilian spacecraft. So both countries have to agree to a ban on orbiting reactors if it is to be effective.

A group of Soviet and United States scientists called for such a ban last spring.

Rep. George Brown Jr. (D) of California has introduced legislation that asks the president to urge the Soviet Union to stop using reactors in Earth orbit. The proposed law would automatically prohibit US use of such reactors if the Soviets agreed.

Safety has been the main consideration behind these efforts. Now the interference with gamma-ray astronomy adds to this concern. Even when used reactors are parked in safe orbits, they can still ruin scientific observations.

This is more than an annoyance for astronomers. It compromises costly projects. The Solar Maximum Mission satellite that astronauts repaired in orbit four years ago suffers from reactor noise. According to a memo issued by NASA last August, reactors could interfere with the $500 million gamma-ray observatory to be launched in 1990. They could also hurt the mission of a planned Soviet gamma-ray satellite.

Neither the scientists' petition nor the Brown bill would prohibit reactors on deep space probes or at a moon base. They would outlaw only use in Earth orbit.

The incoming Bush administration should not wait for congressional prodding to seek a ban on orbiting reactors. It's silly to let these radioactive derelicts accumulate a few hundred miles overhead.

A Tuesday column