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Colder than Space

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artists impression of Astro-EFebruary 8, 2000 -- Astro-E, the Japanese-U.S. X-ray spacecraft poised for a Feb. 8 launch, will showcase an entirely new technology in X-ray detection that not only will serve as a test bed for future missions but also will earn the distinction of being the coldest known object in space.

"This new mission allows us to apply a piece of whiz-bang new technology to the exploration of the Universe," said Dr. Alan N. Bunner, Science Director of NASA's Structure and Evolution of the Universe program.

Above: An artist's impression of ASTRO-E, courtesy of Institute for Space and Astronautical Sciences

The new instrument is the X-ray Spectrometer (XRS), developed jointly by NASA's Goddard Space Flight Center, Greenbelt, MD, and Japan's Institute of Space and Astronautical Science (ISAS). The XRS measures the heat created by individual X-ray photons, as opposed to converting X-rays to electrical charges and then collecting that charge, which is the mechanism in other X-ray detectors.

Using this new technique, it is possible to measure the energies of individual X-rays with a precision approximately 10 times greater than with previous X-ray sensors. To sense the heat of a single photon, however, the XRS detector must be cooled to an extremely low temperature, only 0.060 Kelvin, or about - 460 degrees Fahrenheit.

Below: This animation illustrates the basic operating principles of the XRS microcalorimeter. For more information, visit the XRS page at the Astro-E Learning Center.

see caption This essentially makes the XRS detector the coldest object in space. The absence of all heat, called absolute zero, is 0.0 Kelvin; the coldest reaches of space are a balmy three Kelvin.

"This increased precision for measuring X-rays should allow fundamental breakthroughs in our understanding of essentially all types of X-ray emitting sources, especially material very close to black holes and the X-ray emitting gas in the vast spaces between the individual galaxies that make up clusters of galaxies," said Dr. Richard Kelley, XRS Principal Investigator at Goddard.

Astro-E's targets include: clusters of galaxies; supermassive black holes; neutron stars; supernova remnants; stellar coronae of stars 10,000-times more active than our Sun; and a study of the history of how chemicals are made throughout the Universe.

Astro-E is primarily a spectroscopy mission, which means the satellite's instruments will study the "colors" of X-ray light, much like a prism breaks visible light into the colors of the rainbow. While the recently launched Chandra X-ray Observatory excels in producing X-ray images, Astro-E excels in producing spectra. In this regard, Astro-E complements Chandra, analyzing the light that Chandra sees and determining the temperature, velocity and composition of the gas producing those X-rays.

see captionRight: The Electromagnetic Spectrum. The wavelength of radiation produced by an object is usually related to its temperature. [learn more about x-rays]

Along with the XRS are four X-ray Imaging Spectrometer (XIS) instruments, a collaboration among Japanese universities and institutions and the Massachusetts Institute of Technology Center for Space Research, and the Hard X-Ray Detector (HXD), built by the University of Tokyo and ISAS. Both the XRS and XIS instruments will analyze X-ray photons focused by individual X-ray telescopes, built at Goddard by a team led by Dr. Peter J. Serlemitsos.

The imaging instrument utilizes detectors similar to those flown on ASCA, Astro-E's precursor, yet with twice the collection efficiency at certain X-ray wavelengths. The Hard X-Ray Detector will extend Astro-E's observation ability into the "hard" or higher-energy X-ray wavelengths with the highest sensitivity ever achieved.

see captionRight: ASTRO-E will carry five foil X-Ray Telescopes, pictured here. Four of them will be in front of an XIS, the fifth will be in front of the XRS. These telescopes play an important role. Just as an optical telescope collects light so your eye or a CCD camera can process it, the X-ray Telescopes collect light in the form of X-ray photons, allowing the instruments behind them to process those photons. [more information]

Astro-E will be launched on an M-V rocket from the Kagoshima Space Center, located on the southern tip of the Japanese island of Kyushu. The observatory's expected mission lifetime is five years (two years for the X-Ray Spectrometer, with the depletion of cryogenic gases). Astro-E will attain a near-Earth circular orbit of approximately 341 miles (550 kilometers). Its payload weighs 3,630 pounds (1,650 kilograms), and measures 20.8 x 17.28 x 6.72 feet (6.5 x 5.4 x 2.1 meters).

With its official name to be bestowed after deployment, Astro-E will join the recently launched European X-ray Multi- Mirror Mission and NASA's Chandra X-ray Observatory, ushering in what many experts are calling the decade of X-ray astronomy. Astro-E is the fifth in a series of Japanese satellites devoted to studying celestial X-ray sources. Previous missions are Hakucho, Tenma, Ginga, and ASCA. ASCA, launched Feb. 20, 1993 and formerly known as ASTRO-D, is still active.Web Links

ASTRO-E Learning Center -basic information about Astro-E from the Goddard Space Flight Center

Chandra X-ray Observatory home page -from Harvard

X-Rays - Another Form of Light - the basics of X-rays from the Chandra home page at Harvard