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Home | Update | LATEST ISSUE | Gallery | FR Profile | Datafiles | FR 5/98 AXAF: HUBBLES NEW COLLEGUE by Christopher Hess Hubble is getting support. NASA's space telescope has been in orbit since 1990, taking spectacular pictures from the depth of the universe. However, the Hubble Space Telescope does not cover the entire electromagnetic spectrum. It specialises in visible light ranging into the ultraviolet area. The Compton Gamma Ray Observatory (GRO), which was launched in 1991, catches gamma rays at the upper end of the spectrum, generated by space objects in the far distance. The observation of X-rays, which are between ultraviolet and gamma rays, has not been covered by NASA for quite a few years. Two High Energy Astronomy Observatories (HEAO) were deployed between 1978 and 1982, detecting many X-ray sources within and outside our galaxy. The new Advanced X-ray Astrophysics Facility (AXAF) is supposed to bridge the gap between HST and GRO towards the end of 1998. The resolution of this telescope is about ten times better and its sensitivity is 100 times greater than HEAO-2, which is also known as Einstein Observatory. AXAF is the largest X-ray telescope to date and its task will be to examine the birth and death of galaxies and other energy-laden phenomena. The recording of X-rays via the AXAF will allow to generate picture-like images of very distant objects, comparable to images received through optical telescopes in the visible light region. AXAF's mirrors have been assembled in a special array for this task. Because of their short wave length, X-rays are not reflected off the surface of conventional mirrors. This is why NASA's new X-ray telescope uses four slightly cone shaped mirrors, which fit into one another like bottomless glasses. This assembly allows a grazing incidence of the X-rays which are focussed onto the focal area behind the mirrors - much like a flat stone skipping on the water surface. The biggest mirror has a diameter of approximately 1.2meters. The focal length of the telescope is 10 meters. AXAF weighs around 5.2 tons, is 11.9 meters long and has a diameter of 4.2 meters. The span of the solar panels is 19.5 meters. The development of the X-ray telescope is lead by the Marshall Space Flight Centre for the Office of Space Science at NASA Headquarters. The main contractor for AXAF is the TRW Space & Electronics Group in Redondo Beach, California. The glass used for the mirrors is supplied by Schott Glaswerke in Mainz. The mirrors were built by Hughes Danbury Optical Systems and integrated by Eastman Kodak in Rochester, New York. Ball Aerospace in Boulder, Colorado, is responsible for integrating all the instruments. With the installation of the two solar panels at the beginning of March, TRW has now finished the assembly of the AXAF. The satellite has already completed its first pre-launch tests. The first of which was an acoustic test, in which the AXAF was exposed to a noise level similar to the one experienced in the payload bay of the Space Shuttle during launch. Further environmental tests are planned at a later stage. At the end of 1997 the program was delayed because TRW experienced problems with the configuration and programming of the company's integrated automated spacecraft test system. As a result, the flight with Space Shuttle Columbia (STS-93) was postponed from August to 3 December, 1998. After AXAF is released from the Shuttle, it will be brought to an extreme elliptical and high orbit, powered by its own internal propulsion system. At the closest point of the orbit, AXAF will have an altitude of 10,000km. At the furthest point, the satellite will be up to 140,000km away from Earth. The elliptical orbit optimises the telescope's available observation time above 60,000km. Below this height, X-rays from space are masked by radiation from earth, which makes any observation impossible. A few years after the planned start of NASA's new telescope, Hubble, GRO and AXAF are getting a European colleague. The ESA X-ray telescope XMM (X-ray Multi-Mirror) is supposed to spot up to one million X-ray sources and carry out spectroscopic examinations. From page 40 of FLUG REVUE 5/98 Home | Update | LATEST ISSUE | Gallery | FR Profile | Datafiles | FR 5/98 Copyright 1998 by Motor-Presse Stuttgart. All rights reserved. Last updated April 7, 1998 FLUG REVUE, Ubierstr. 83, 53173 Bonn, Germany