Don Savage Headquarters, Washington, DC January 30, 1995 (Phone: 202/358-1547) Steve Roy Marshall Space Flight Center, Huntsville, AL (Phone: 205/544-6535) RELEASE: 95-10 NASA'S X-RAY TELESCOPE MIRRORS COMPLETED AHEAD OF SCHEDULE A space-based observatory, under construction for NASA, has met an important milestone -- polishing and measurement of the observatory's eight mirrors, one of the project's toughest technical challenges, has been completed four months ahead of schedule at Hughes Danbury Optical Systems (HDOS), Danbury, CT. Data from the observatory, called the Advanced X-ray Astrophysics Facility (AXAF), will be used to study X-ray radiation and is expected to significantly improve scientific understanding of some of the most energetic and violent processes in the universe. Launch of the AXAF is scheduled for September 1998. The observatory will produce picture-like images and spectrograms which will yield information on temperature and chemical composition of the objects it observes. Among the objects that will be observed are neutron stars, black hole candidates, debris from supernova explosions, quasars, the centers of active galaxies and hot gas in individual galaxies and clusters of galaxies. "The reason for this success was that we invested the time up front to understand the polishing and metrology process," said AXAF Telescope Project Manager John Humphreys. "The first mirror took nine lengthy polishing cycles to complete. We then applied a process of continual improvements to get the job done much faster and were able to complete the final mirror in only three polishing cycles." Humphreys said a plan has been put into place to exploit these early deliveries and get a head start on the next set of challenges -- coating the mirrors with a reflective iridium layer. The measurements of the just-completed mirrors indicate that the shape and smoothness meet the exacting program goals. Their average smoothness, measured at 3 ngstroms, is the width of just three atoms. Certifying the accuracy of measurements on a scale this small proved to be a challenge for engineers. -more- -2- "Fabrication required measurements so precise that there was no existing standard of reference in the world. In fact, the National Institute of Standards and Technology has expressed interest in using the technology developed for AXAF in a national facility for metrology," said Humphreys. The most critical part of this mirror metrology process has been the independent measurements and cross- checks. Critical measurements were made using several techniques or pieces of equipment to rule out the possibility of a flaw in the measuring equipment itself. In addition, over 68 people from twelve separate organizations have participated in the review of AXAF mirror procedures, fabrication, metrology and test data. The mirrors of AXAF's X-ray telescope are very different from those in optical telescopes. They are cylindrical in shape with inner surfaces finely polished to precise, mathematically determined, geometric shapes. X- rays enter the front of the telescope and reflect off of the inner surfaces of the mirrors at very shallow or grazing angles, almost like a stone skipping over water, finally coming to a focus behind the mirrors. The cylinder-like mirrors are used in pairs, with each pair "nested" inside the next larger set so that the frontal, energy-collecting area of the telescope is as large as possible. AXAF's mirror assembly holds four pairs of cylindrical mirrors. AXAF will produce spectrographic information about the temperature and chemical composition of objects by separating the radiation received according to wavelength, much as a prism splits visible light into constituent colors. The observatory will produce 'picture-like' X-ray images analogous to images in visible light made by traditional telescopes. Once in orbit and operational, AXAF will provide scientists with the most detailed views of the universe ever obtained through observation of X-ray emissions. The next step for AXAF is the precise alignment of the mirrors. The first and largest pair of mirrors currently are being aligned in a pathfinder mirror assembly at Eastman-Kodak Company (EKC), Rochester, NY. After completion of this pathfinder alignment effort, the mirrors will be shipped to Optical Coating Laboratory, Inc. (OCLI) in Santa Rosa, CA, where they will be coated with iridium, returned to Kodak, integrated and aligned into the High Resolution Mirror Assembly. The remaining six mirrors for AXAF also will be coated at OCLI and sent to EKC for assembly. In 1996, all of the AXAF flight optics and detectors required to meet the science mission objectives will be aligned and tested in the X-ray Calibration Facility at Marshall. AXAF is designed to be complementary to NASA's Great Observatories already in orbit -- the Hubble Space Telescope launched in 1990, and the Compton Gamma-Ray Observatory, launched in 1991. Each observatory makes observations of stars, galaxies, and other astronomical objects in distinct and separate wavelengths of energy, including visible light, ultraviolet, gamma rays, and, in the case of AXAF, X-rays. -more- -3- The AXAF development team consists of NASA, the Smithsonian Astrophysical Observatory, TRW, HDOS, EKC and the Marshall Space Flight Center, which manages the project for NASA's Office of Space Science, Washington, DC - end - EDITOR'S NOTE: An artist's depiction of AXAF is available to news media representatives by calling the Broadcast & Imaging Branch on 202/358-1900. Photo number is: Color: 95-HC-62 Black and White: 95-H-64 NASA press releases and other information are available automatically by sending an Internet electronic mail message to domo@hq.nasa.gov. In the body of the message (not the subject line) users should type the words "subscribe press-release" (no quotes). The system will reply with a confirmation via E-mail of each subscription. A second automatic message will include additional information on the service. Questions should be directed to (202) 358-4043.