Sky & Telescope September 1983 [antikvár]

Space Telescope: Problems and ProgressFor THOSE involved with NASA's Space Telescope, June 15th was a study in contrasts. On the Homewood campus of Johns Hopkins University in Baltimore, hundreds of astronomers gathered at a gala dedication of the new science institute that will become the focus for the study of ST's data. Meanwhile, at NASA's Washington headquarters some 35 miles away, administrator James Beggs fine-tuned his presentation for a congressional subcommittee on the project's technical and management problems. These surfaced abruptly in March and have postponed the launch of ST until mid-1986. Regrettably, another year's delay means that the telescope will be unavailable when Halley's comet nears perihelion or when Voyager 2 reaches Uranus.Still, there is little doubt that, once in operation. Space Telescope will revolutionize much of observational astronomy. It is the agency's largest space-science venture since the Viking mission to Mars. But many loose ends remain, even though work on the satellite began in earnest six years ago. Initially, the most formidable task appeared to be fashioning the optics. To maximize the gain from spacebome observations, NASA realized that the surface of the primary mirror (2.4 meters, or 94 inches. across) would have to come as close to perfection as technology would permit.The design calls for an optical train with a combined wavefront error no more than '/jo the wavelength of orange light, about one-millionth of an inch. It must also be responsive to everything from 1200 ang-Wfaen launched by the Space Shuttle in 1986, the Space Telescope (upper right) will weigh about 23,300 pounds and measure 43.5 feet in length and 14 feet in diameter. Its three major components are a suite of five scientific instruments, the support systems module at the rear that houses them, and the optical telescope assembly (shown in greater detail in this diagram). The orbiting observatory is expected to last 15 years or more. These illustrations were supplied by Perkin-El-mer Corp.stroms (deep in the ultraviolet) to one millimeter (at the edge of the radio spectrum). Such precision yields a spatial resolution of 0.1 arc second, and to exploit this capability ST is required to hold its lock on guide stars for up to 24 hours to within 0.007 arc second the apparent size of this typeface's period (.) viewed from 6Vj miles away!Eight detectors will feast on the light gathered by the primary mirror. Four of the scientific instruments are the High-Speed Photometer, High-Resolution Spectrograph, Faint-Object Spectrograph, and Faint-Object Camera. The fifth, called the Wide-Field/Planetary Camera, is a CCD imaging system that can switch between effective focal ratios of f/12.9 and f/30. Three Fine-Guidance Sensors provide the requisite tracking on stars as faint as magnitude 14.5; since only two are needed at one time, the third will be used for astrometric measurements to magnitude 17. All the instruments are fitted in modular enclosures to permit removal by visiting shuttle astronauts, should replacement or repair be necessary.Ironically, work on the 1.800-pound primary mirror proceeded smoothly, and when completed in late 1981 it actually exceeded the design specifications (see page 128 of the February, 1982, issue). Yet this proved to be one of the few bright spots in a project beset by difficulties. Many of the problems have been attributed simply to "gross underestimation" of the technical challenges involved. But Beggs finds little consolation in that. "Advanced researchand high-risk technical undertakings are the essence of NASA's mission," he says, "and we must continually strive to improve our ability to take on ever more difficult assignments."More central to the ST dilemma is the project's poor organization and management, which were addressed at length in a scathing report submitted in March to the House Appropriations Committee. For a project of this size, NASA usually singles out one of its field centers to oversee a sole primary contractor. However, the construction of Space Telescope is divided between two major contractors (Perkin-Elmer in Danbury, Connecticut, for the optical assembly, and Lockheed's Space SystemsSeptember, 1983. Sky & Telescope 189