Donald Savage
Headquarters, Washington, DC          March 20, 1997
(Phone:  202/358-1547)

Greg Shell
Marshall Space Flight Center, Huntsville, AL
(Phone: 205/544-0034)

Kathy Lestition
Smithsonian Astrophysical Observatory, Cambridge, MA
(Phone:  617/495-7399)

RELEASE: 97-48

ADVANCED X-RAY TELESCOPE MIRRORS PROVIDE SHARPEST FOCUS EVER

    Performing beyond expectations, the high-
resolution mirrors for NASA's most powerful orbiting 
X-ray telescope have successfully completed initial 
testing at Marshall Space Flight Center's X-ray 
Calibration Facility, Huntsville, AL.

    "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,"  said 
Dr. Martin Weisskopf, Marshall's 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 X-ray telescope produces an image by directing 
incoming X-rays to detectors at a focal point some 30 
feet beyond the telescope'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 on orbit, the mirror assembly of 
the Advanced X-ray Astrophysics Facility will be able 
to focus approximately 70 percent of X-rays from a 
source to a spot less than one-half arc second in 
radius. The telescope's resolution is equivalent to 
being able to read the text of a newspaper from half a 
mile away.

    "The telescope's focus is very clear, very sharp," 
said Weisskopf. "It will be able to show us details of 
very distant sources that we know are out there, but 
haven't been able to see clearly."

    In comparison, previous X-ray telescopes -- 
Einstein and Rosat -- were only capable of focusing X-
rays to five arc seconds. The Advanced X-ray 
Telescope's resolving power is ten times greater.

    "Images from the new telescope will allow us to 
make major advances toward understanding how exploding 
stars create and disperse many of the elements 
necessary for new solar systems and for life itself," 
said Dr. Harvey Tananbaum, director of the Advanced X-
ray Astrophysics Facility Science Center at the 
Smithsonian Astrophysical Observatory, in Cambridge, 
MA -- responsible for the telescope's science mission.

    "We will observe X-rays generated when stars are 
torn apart by the incredibly strong gravity around 
massive black holes in the centers of galaxies," added 
Tananbaum.

    On a larger scale, the telescope will play a vital 
role in answering fundamental questions about the 
universe. "The superior quality of the mirrors will 
allow us to see and measure the details of hot gas 
clouds in clusters of galaxies, giving us a much 
better idea of the age and size of the universe," said 
Dr. Leon Van Speybroeck, Telescope Scientist at the 
Smithsonian Observatory.

    "These same observations also will measure the 
amount of dark matter present, providing unique 
insight into one of nature's great puzzles," said Van 
Speybroeck.

    A second phase of testing is now underway at 
Marshall. Calibration of the observatory's science 
instruments began in mid-February. "This phase of 
testing," said Weisskopf, "includes two focal plane 
instruments and two sets of gratings used to analyze 
images and energy distributions from cosmic sources 
seen by the telescope."

    Working around the clock, test teams are taking 
measurements and studying results. "It is very 
exciting," said Weisskopf. "With more than 1,200 
measurements taken, there is already a tremendous 
amount of information for study." 

    The calibration process will end around late 
April. The mirror assembly then will be shipped to TRW 
Space and Electronics Group, Redondo Beach, CA -- 
NASA's prime contractor for the program -- for 
integration into the spacecraft.  The science 
instruments will remain at Marshall for several more 
weeks of testing before being shipped to Ball 
Aerospace and Technologies Corporation in Boulder, CO, 
where they will be integrated into the science 
instrument module before being shipped to TRW.

    The Advanced X-ray Astrophysics Facility is 
scheduled for launch in August 1998 and will join 
NASA's Hubble Space Telescope and Compton Gamma-ray 
Observatory in exploring the universe.

    Marshall manages development of the observatory 
for the Office of Space Science, NASA Headquarters, 
Washington, DC. Using glass purchased from Schott 
Glaswerke, Mainz, Germany, the telescope's mirrors were built by 
Hughes Danbury Optical Systems, Danbury, CT.  The 
mirrors were coated by Optical Coating Laboratory, 
Inc., Santa Rosa, CA; and assembled by Eastman-Kodak 
Company, Rochester, NY.

    The AXAF CCD Imaging Spectrometer instrument was 
developed by Pennsylvania State University, University 
Park, and the Massachusetts Institute of Technology 
(MIT), Cambridge, MA.  One of the two gratings was 
developed by MIT. The other was developed by the Space 
Research Organization Netherlands, Utrecht, 
Netherlands, in collaboration with the Max Planck 
Institute, Garching, Germany. The High Resolution 
Camera instrument was built by the Smithsonian 
Astrophysical Observatory. 

                      -end-

A photograph is available from the NASA Headquarters 
Audio Imaging Branch to news media to illustrate this 
story.  The Photograph number is 97-HC-138.  
Photographs also are available from the Marshall 
Public Affairs office at 205/544-0034.  Images are 
available via the Internet at UFL:

           http://xrtpub.harvard.edu/PRESS/