Swinging within about 55 million miles of the sun every 76 years, Halley's comet has been an object of awe since what may have been the first reported sighting, by Chinese astronomers in 240 B.C. But when this cosmic snowball of ice and dustwith a nucleus between 3 and 6 miles across and a tail millions of miles longstreaks across the sky in 1986, it will be greeted for the first time by five spacecraft. In the vanguard of an international effort to study the comet, the Soviet Union recently launched two 4.5-ton unmanned space probes laden with cameras and sensors. And in an extraordinary show of East-West scientific collaboration, two U.S.-designed comet-dust analyzers are tucked aboard the Soviet vessels. Named Vega 1 and 2, after the first letters from the Russian words for Venus and Halley, the two craft are scheduled to deliver landing modules to the surface of Venus in June 1985; they will then spin off to rendezvous nine months later within 6,000 miles of Halley's.
Vega 1 and 2 will be joined by three other spacecraft. Next January, Japan will launch its MST5 probe, followed in July by the eleven-nation European Space Agency's spacecraft, Giotto, and Japan's second probe, PlanetA, in August. The five craft will be coordinated to analyze the comet from different distances, with the closest probe, Giotto, programmed to come within 300 miles.
The closeup look at Halley's is considered important because it may provide clues about the early solar system. Perhaps more notable still, the participants from all nations have promised to share their results.