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ASCA mission graphic

Advanced Satellite for Cosmology and Astrophysics

Phase: Past

Launch Date: February 20, 1993

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ASCA (formerly named Astro-D) was Japan's fourth cosmic X-ray astronomy mission, and the second for which the United States provided part of the scientific payload. The satellite was successfully launched on February 20, 1993 and acquired science data until July of 2000. ASCA re-entered the Earth's atmosphere on March 2, 2001.

The first eight months of the ASCA mission were devoted to performance verification. Having established the quality of performance of all ASCA's instruments, the project changed to a general/guest observer for the remainder of the mission. In this phase the observing program was open to astronomers based at Japanese and U.S. institutions, as well as those who were located in member states of the European Space Agency.

ASCA was the first X-ray astronomy mission to combine imaging capability with a broad pass band, good spectral resolution, and a large effective area. The mission also was the first satellite to use CCDs for X-ray astronomy. With these properties, the primary scientific purpose of ASCA was the X_ray spectroscopy of astrophysical plasmas-especially the analysis of discrete features such as emission lines and absorption edges.

ASCA carried four large-area X-ray telescopes. At the focus of two of the telescopes is a Gas Imaging Spectrometer (GIS), while a Solid-state Imaging Spectrometer (SIS) is at the focus of the other two. The GIS is a gas imaging scintillation proportional counter and is based on the GSPC that flew on the second Japanese X-ray astronomy mission TENMA. The two SIS are identical Charge Coupled Device (CCD) cameras were provided by a hardware team from MIT, Osaka University and ISAS.

Science Highlights

  • The sensitivity of ASCA's instruments allowed for the first detailed, broad-band spectra of distant quasars to be derived.
  • ASCA's suite of instruments provided the best opportunity at the time for identifying the sources whose combined emission makes up the cosmic X-ray background.
  • ASCA saw broad iron lines proving that the active nucleus of a galaxy is a super-massive black hole.
  • ASCA provided analysis of the elemental composition, heterogeneity and particle acceleration of supernova remnants by dispersing X-rays.
  • ASCA saw X-ray emissions from a newly-formed protostar.
  • ASCA saw a two-temperature structure of hot plasma in a galaxy cluster.

Last Updated Date: May 27, 2015

Related Links
  • Japanese ASCA Site -