March 20, 1997
ADVANCED X-RAY TELESCOPE MIRRORS PROVIDE SHARPEST FOCUS EVER
Donald Savage, Headquarters, Washington, DC
Michael Braukus, Headquarters, Washington, DC (Phone: 202/358-1979)
Dave Drachlis, Marshall Space Flight Center, Huntsville, AL (Phone: 205/544-0034)
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.
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/