Advanced Satellite for Cosmology and Astrophysics

ASCA

The ASCA Spacecraft (credit: ISAS and NASA GSFC)
Organization	ISAS / NASA
Wavelength regime	X-ray
Orbit Height	500–600 km
Orbit period	95 min
Launch date	20 February 1993 at 02:20 UTC
Launched from	Kagoshima Space Center, Japan
Launch Vehicle	M-3SII
Deorbit date	2 March 2001
Mass	420 kilograms (930 lb)
Webpage	http://heasarc.gsfc.nasa.gov/docs/asca/
Physical Characteristics
Telescope Style	Wolter telescope - paired grazing incidence hyperbolic and parabolic foil mirrors
Diameter	1.2m
Collecting Area	1300 cm² @ 1 keV, 600 cm² @ 7 keV
Effective Focal Length	3.5 m
Instruments
XRT	X-ray telescopes (4)
GIS	Imaging Spectrometer
SIS	Imaging Spectrometer

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.

External links

• JAXA/ISAS ASCA official page
• NASA/Goddard Space Flight Center ASCA information page