Technology: Sticky start for world's largest telescope

 作者:谯圳晋     |      日期:2019-02-28 02:10:02
By JEFF HECHT in BOSTON Technical hitches are holding up the smooth running of the world’s largest optical telescope. ‘The telescope at times has not been behaving very well,’ admits project scientist Jerry Nelson. But when it has been working, the 10-metre Keck Telescope, in Mauna Kea in Hawaii, has impressed astronomers with images and spectra of objects too faint to be detected by other telescopes. Planners allocated 70 per cent of the telescope’s available time from January to June to science work, and that will rise to more than 80 per cent in the rest of the year, says Peter Gillingham, director of operations for the telescope. But in the spring, astronomers lost 11 per cent of ‘science time’ to software problems, 10 per cent to hardware problems, and 27 per cent to unusually bad weather. ‘The most persistent problems have been with the timing system,’ says Gillingham. These caused the telescope to point at the wrong place. The motor that was designed to shift the telescope rapidly between targets sometimes stuck and slipped, forcing operators to move it slowly while they tried to isolate the source of the problem. During the harsh winter (despite the telescope’s proximity to the equator) there were problems rotating the dome and opening the dome shutter for observations. Other problems came from bugs in the customised software used in the control system. Keck took its first picture of the sky on 24 November 1990, but the instrument was far from complete, with just 9 of its 36 mirror segments installed. Most of the segments were sent to Eastman-Kodak in the US to take advantage of a new milling technique which uses an ion beam to produce an almost perfect surface. This enhanced the optical quality, but slowed assembly, so the last of the 36 mirrors was only in place last November. The delay was not exceptional for a large telescope; designers know it takes a long time to adjust such instruments, especially those with innovative designs like Keck’s mirror, which is segmented. Engineering to ready the telescope for full use took up most time on Keck until January; last year it notched up only 15 to 20 nights of scientific observations, says Gillingham. Debugging the innovative segmented mirror design caused delays. Operators must fine-tune the location, shape, and alignment of each mirror segment, which is mounted on a harness with 30 individual adjustment screws. Despite the difficulties, Keck is widely regarded as a success. Even one of the design’s most outspoken critics, Harland Epps of the University of California at Santa Cruz,