X-ray telescope will provide sharpest images.

Performing beyond expectations, the high-resolution mirrors for NASA's most powerful orbiting X-ray telescope successfully have completed initial testing at Marshall Space Flight Center's X-ray Calibration Facility in Huntsville, Ala. "We have the first ground test images ever generated by the telescope's mirror assembly, and they are as good as -- or better than -- expected," notes Martin Weisskopf, chief scientist for NASA's Advanced X-ray Astrophysics Facility (AXAF).

The mirror assembly, four pairs of precisely shaped and aligned cylindrical mirrors, will form the heart of NASA's third great observatory. The telescope produces an image by directing incoming X-rays to detectors at a focal point some 30 feet beyond the instrument's mirrors. The greater the percentage of X-rays brought to focus and the smaller the size of the focal spot, the sharper the image.

Tests show that, in orbit, the mirror assembly will be able to focus approximately 70% of X-rays from a source to a spot less than one-half an arc second in radius. An arc second is an extremely small angular measure, one-3,600th of a degree. The telescope's resolution is equivalent to being able to read the text of a newspaper from half a mile away. In comparison, previous X-ray telescopes were capable of focusing X-rays to five arc seconds. The Advanced X-ray telescope's resolving power is 10 times...