The European Space Agency's launch of a 1,000-pound spacecraft to probe Halley's comet next year is on schedule for July from the agency's spaceport in French Guiana.
In the mission, the most ambitious scientific space project attempted by the Europeans, the spacecraft, called Giotto, is to pass closer to the comet's nucleus than any other spacecraft when the comet circles the sun next spring.
Giotto's close encounter may provide scientists with better clues about the comet's composition: whether it is a solid, ice-covered rock, as some have suggested, or multiple fragments fused together by exotic ices.
"If you assume the nucleus of Halley's comet is the size of Manhattan Island, you ought to be able to see Times Square," Hugh Mooney, senior manager of British Aerospace, builders of the $40 million spacecraft, told a news conference recently. "Whatever we see will be the first look at the nucleus of any comet that anybody has ever had."
The European mission involves an eight-month voyage from Earth culminating in a 43-mile-per-second encounter with the comet that will last less than four hours. Because Giotto is expected to come within 300 miles of the comet's nucleus, it may be so sandblasted by dust particles from the comet's tail that it disintegrates.
"Even though we expect the craft to be hit by particles no heavier than one-tenth of a gram, the collisions will be the same as a subcompact car hitting something at 50 miles an hour," Mooney said. "There is a reasonable possibility that the spacecraft will not survive."
The only instrument not ready for the flight, he said, is a camera built by West Germany's Max Planck Institute, where it is undergoing tests. Mooney said the camera, which could reveal features as small as 60 feet across on the comet's surface, will be installed on Giotto after the spacecraft is placed atop an Ariane 1 rocket booster at the launch center.
Giotto's encounter with Halley's comet is expected to take place March 13, when the comet is 84 million miles from the sun and 90 million miles from Earth. Two Soviet spacecraft already on their way to a rendezvous with Venus are expected to pass near the comet a few days before Giotto does, and a Japanese spacecraft named Planet A to be launched later this year is to observe the comet from a distance of about 200,000 miles.
The United States, which has no separate mission to Halley's comet, intends to photograph the comet from low Earth orbit in March using three ultraviolet telescopes on the space shuttle. The United States is providing navigational aid to ESA and the Soviet Union, however, to help target their spacecraft to meet Halley's comet when it swings around the sun on its 76-year orbit through the solar system.
The National Aeronautics and Space Administration also has retargeted two spacecraft -- one in orbit around Venus and another that had been in orbit around the sun -- to observe the comet.
Giotto is named after Florentine painter Giotto di Bondone, who saw Halley's comet when it was nameless in 1301. A few years later, Giotto incorporated the comet as the Star of Bethlehem in a painting of the Magi's visit to Bethlehem for a fresco in a chapel in Padua.
The comet is named for Sir Edmund Halley, who successfully predicted that the comet seen in 1682 would return in 1758.