Advanced Satellite for Cosmology and Astrophysics
Encyclopedia
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| The ASCA Spacecraft (credit: ISAS and NASA GSFC) | |
| Organization | ISAS Institute of Space and Astronautical Science is a Japanese national research organization of astrophysics using rockets, astronomical satellites and interplanetary probes. It is a division of Japan Aerospace Exploration Agency .- History :... , NASA NASA The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research... |
| Wavelength regime | X-ray |
| Orbit Height | 500–600 km |
| Orbit period | 95 min |
| Launch date | 20 February 1993 |
| Deorbit date | 2 March 2001 |
| Mass | 420 kg |
| Webpage | http://heasarc.gsfc.nasa.gov/docs/asca/ |
| Physical Characteristics | |
|---|---|
| Telescope Style | Wolter telescope Wolter telescope A Wolter telescope is a telescope for X-rays using only grazing incidence optics. Visible light telescopes are built with lenses or parabolic mirrors at nearly normal incidence. Neither works well for X-rays. Lenses for visible light are made of a transparent material with an index of refraction... - 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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
.
X-ray astronomy mission
ASCA was the first X-ray astronomy missionHistory of X-ray astronomy
History of X-ray astronomy begins in the 1920's with interest in short wave communications for the U.S. Navy. This led to the study of the ionosphere. By 1927 interest in going beyond studies with short waves led to developing theories pertaining to putting Goddard's rockets into the upper...
to combine imaging capability with a broad pass band, good spectral resolution
Spectral resolution
The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum...
, and a large effective area. The mission also was the first satellite to use CCD
CCD
-Science:*Carbonate compensation depth, a property of oceans*Colony collapse disorder, a phenomenon involving the abrupt disappearance of the worker bees in a beehive or Western honey bee colony...
s for X-ray astronomy
X-ray astronomy
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...
. With these properties, the primary scientific purpose of ASCA is the X-ray spectroscopy
X-ray spectroscopy
X-ray spectroscopy is a gathering name for several spectroscopic techniques for characterization of materials by using x-ray excitation.-Characteristic 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 telescope
X-ray telescope
An X-ray telescope is a telescope that is designed to observe remote objects in the X-ray spectrum. In order to get above the Earth's atmosphere, which is opaque to X-rays, X-ray telescopes must be mounted on high altitude rockets or artificial satellites.-Optical design:X-ray telescopes can use...
s. 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
ROSAT
ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
(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.