Word: spacecrafts
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...scientist likened it to sinking a 500-mile putt. Superlatives were certainly in order last week as the semiautonomous robot completed the second lap of its epic flight: a rendezvous with the giant ringed planet Saturn, the spectacular finale to two ambitious decades of planetary exploration by unmanned U.S. spacecraft...
Racing toward Saturn at 54,000 m.p.h.-20 times as fast as a speeding bullet-the 1,800-lb. spacecraft came within a cosmic hair of the planet's stormy cloud tops, clearing them by 63,000 miles. Then it plunged downward behind the huge gaseous sphere and passed through a large gap near the edge of the thin disc of icy debris that forms Saturn's multi-hued rings. Finally, like a pebble in a great celestial slingshot, it was sent hurtling off toward Uranus on a new course created by the powerful pull of Saturn...
Voyager came closest to Saturn just before the 1½-hour period when the spacecraft was behind the planet, totally cut off from the earth. But the semi-intelligent machine continued operations under the command of its preprogrammed computers, taking pictures, performing experiments and storing the information on tape. Not until Voyager 2 emerged from behind Saturn and again began radioing back data did scientists learn that something had gone wrong. As Voyager 2 crossed the rings, the playback showed, the cameras began missing their targets. Somehow the spacecraft's movable "scan platform," which acts as an aiming mechanism...
...platform's horizontal movements? Or was there a failure in the electronics or perhaps in the gears themselves? No one could say, even after hours of patient long-distance troubleshooting (it takes nearly an hour and a half to send a radio command to the far-off spacecraft). By the next day JPL controllers had found they could at least get the frozen platform to swing through a few degrees of arc, though not smoothly or precisely enough to aim the instruments properly. By moving it through ever larger arcs, they hoped that they might eventually work it free...
Still another experiment involves Voyager 2's photopolarimeter, a light-measuring device that failed on the first flight.. As the spacecraft approaches the planet, the instrument will be aimed through the rings at Delta Scorpii, a far-off star. By measuring disruptions (or blinking) of the starlight caused by the intervening ring material, the scientists should get the most precise data yet on the number of rings, their density and width and the size of the stuff they are made...