Advanced Satellite for Cosmology and Astrophysics
|The ASCA Spacecraft (credit: ISAS and NASA GSFC)|
|Orbit Height||500–600 km|
|Orbit period||95 min|
|Launch date||20 February 1993|
|Deorbit date||2 March 2001|
|Telescope Style||Wolter telescope - paired grazing incidence hyperbolic and parabolic foil mirrors|
|Collecting Area||1300 cm² @ 1 keV, 600 cm² @ 7 keV|
|Effective Focal Length||3.5 m|
|XRT||X-ray telescopes (4)|
ASCA (formerly named ASTRO-D) is the fourth cosmic X-ray astronomy mission by Japan's (JAXA), and the second for which the United States is providing part of the scientific payload. The satellite was successfully launched on February 20, 1993. 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 is open to astronomers based at Japanese and US institutions, as well as those who are located in member states of the European Space Agency.
X-ray astronomy mission 
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 is 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.
Significant contributions 
The ASCA was launched by ISAS (Institute of Space and Astronautical Sciences), Japan.
The sensitivity of ASCA's instruments allowed for the first detailed, broad-band spectra of distant quasars to be derived. In addition, 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.
It performed over 3000 observations, and produced over 1000 publications in refereed journals so far. The ASCA archive contains significant amounts of data for future analyses. Furthermore, the mission is termed highly successful when reflecting on what scientists in many counties have accomplished using ASCA data up to this time.
The US has contributed significantly to ASCA's scientific payloads. In return, 40% of ASCA observing time was made available to US scientists. (ISAS also opened up 10% of the time to ESA scientists as a good-will gesture.) In addition, all ASCA data enter the public domain after a suitable period (1 year for US data, 18 months for Japanese data) and become available to scientists worldwide. The design of ASCA was optimized for X-ray spectroscopy; thus it complimented ROSAT (optimized for X-ray imaging) and RXTE (optimized for timing studies). Finally, ASCA results cover almost the entire range of objects, from nearby stars to the most distant objects in the universe.
Mission end 
The mission operated successfully for over 7 years until attitude control was lost on July 14, 2000 during a geomagnetic storm, after which no scientific observations were performed. ASCA reentered the atmosphere on March 2, 2001 after more than 8 years in orbit.
The primary responsibility of the U.S. ASCA GOF was to enable U.S. astronomers to make the best use of the ASCA mission, in close collaboration with the Japanese ASCA team.
- Advanced Satellite for Cosmology and Astrophysics. Launch Date: February 20, 1993. Science Missions. "ASCA" (online web page). NASA's science program. NASA. Retrieved 2011-09-15.
- Tanaka, Yanno; Inoue, Hajime; and Holt, Stephen S.. (June 1994). "The X-ray astronomy satellite ASCA" (Full text article is available via the link in the title). Publications of the Astronomical Society of Japan. 46, no. 3, p. (3): L37–L41. Bibcode:1994PASJ...46L..37T. doi:10.1007/BF01581810. ""The scientific capabilities of ASCA and some aspects related to its operation and observations are briefly described"."
- 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.
- Tsusaka, Yoshiyuki; Suzuki, Hisanori; Yamashita, Koujun; Kunieda, Hideyo; Tawara, Yuzuru; Ogasaka, Yasushi; Uchibori, Yasuhiro; Honda, Hirohiko et al. (1995). "Characterization of the Advanced Satellite for Cosmology and Astrophysics x-ray telescope: Preflight calibration and ray tracing". Applied Optics (Online abstractBibcode:1995ApOpt..34.4848T. doi:10.1364/AO.34.004848. PMID 21052325.) 34 (22): 4848–56.
- ASCA's Significant Contributions to Astrophysics. Goddard Space Flight Center.
- ASCA Project Scientist: Dr. Nicholas E. White "The ASCA Mission (1993-2000)" (Online web page). Goddard Space Fight Center. May 20, 2011. Retrieved 2011-09-15.