The Advanced Satellite for Cosmology and Astrophysics (ASCA, formerly named ASTRO-D) was the fourth cosmic X-ray astronomy mission by

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

, and the second for which the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

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

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

s based at Japanese and U.S. institutions, as well as those located in member states of the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

X-ray astronomy mission

ASCA was the first X-ray astronomy mission to combine imaging capability with a broad

passband A passband is the range of frequency, frequencies or wavelengths that can pass through a Filter (signal processing), filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all t ...

, good

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. It is usually denoted by \Delta\lambda, and is closely related to the resolvi ...

, and a large effective area. The mission also was the first satellite to use CCDs for

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 ...

. With these properties, the primary scientific purpose of ASCA was the

X-ray spectroscopy X-ray spectroscopy is a general term for several Spectroscopy, spectroscopic techniques for characterization of materials by using x-ray radiation. Characteristic X-ray spectroscopy When an electron from the inner shell of an atom is excited b ...

of astrophysical plasmas, especially the analysis of discrete features such as

emission lines A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

and absorption edges. ASCA carried four large-area

X-ray telescope An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets ...

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. 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 A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

(CCD) cameras were provided for the two SISs by a hardware team from MIT, Osaka University and ISAS.

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 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.

Mission end

The mission operated successfully for over 7 years until attitude control was lost on 14 July 2000 during a

geomagnetic storm A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere that is driven by interactions between the magnetosphere and large-scale transient Plasma (physics), plasma and magnetic field structur ...

, 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.

References

External links

ASCA website
by JAXA
ASCA website
by NASA {{DEFAULTSORT:Advanced Satellite For Cosmology And Astrophysics 1993 in spaceflight Satellites of Japan Space program of Japan Space telescopes X-ray telescopes