Advanced Satellite for Cosmology and Astrophysics

Advanced Satellite for Cosmology and Astrophysics

Names	ASTRO-D, Asuka
Mission type	X-ray observatory
Operator	ISAS / NASA
COSPAR ID	1993-011A
SATCAT no.	22521
Website	http://heasarc.gsfc.nasa.gov/docs/asca/
Mission duration	Final: 8 years, 10 days
Spacecraft properties
Manufacturer	NEC
Launch mass	420 kg (930 lb)
Dimensions	4.7 m (15 ft) long
Start of mission
Launch date	20 February 1993, 02:20 (1993-02-20UTC02:20) UTC
Rocket	Mu-3SII, mission M-3SII-7
Launch site	Kagoshima Space Center, Japan
Contractor	ISAS
End of mission
Disposal	deorbited
Decay date	2 March 2001, 14:20 (2001-03-02UTC14:21) UTC
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Eccentricity	0.01
Perigee altitude	523.6 km (325.3 mi)
Apogee altitude	615.3 km (382.3 mi)
Inclination	31.1°
Period	96.09 minutes
Epoch	20 February 1993
Main telescope
Type	Wolter
Diameter	1.2 m (3.9 ft)
Focal length	3.5 m (11 ft)
Collecting area	1,300 cm2 (200 sq in) @ 1 kev 600 cm2 (93 sq in) @ 7 keV
Wavelengths	X-ray, SIS: 3–0.12 nm (0.4–10 keV)[1] GIS: 1.8–0.12 nm (0.7–10 keV)[2]
Instruments XRT X-ray Telescope SIS Solid-State Imaging Spectrometer GIS Gas Imaging Spectrometer

The Advanced Satellite for Cosmology and Astrophysics (ASCA, formerly named ASTRO-D) was the fourth cosmic X-ray astronomy mission by JAXA, and the second for which the United States provided part of the scientific payload. The satellite was successfully launched on 20 February 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 spacecraft provided science observations 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 located in member states of the European Space Agency.^[3][4]

ASCA was the first X-ray astronomy mission to combine imaging capability with a broad passband, 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.^[3][4] 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 identical charge-coupled device (CCD) cameras were provided for the two SISs by a hardware team from MIT, Osaka University and ISAS.

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.^[3][5]

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 U.S. contributed significantly to ASCA's scientific payloads. In return, 40% of ASCA observing time was made available to U.S. 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 U.S. data, 18 months for Japanese data) and become available to scientists worldwide. The design of ASCA was optimized for X-ray spectroscopy; thus it complemented 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.^[6]

The mission operated successfully for over 7 years until attitude control was lost on 14 July 2000 during a geomagnetic storm, after which no scientific observations were performed. ASCA reentered the atmosphere on 2 March 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.^[7]

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

• ASCA website by JAXA
• ASCA website by NASA