ASCA Overview

ASCA mirror module
Close-up of one of the ASCA mirror modules; each line is a mirror foil.

ASCA was Japan’s fourth cosmic X-ray astronomy mission, and the second for which the United States provided part of the scientific payload. The satellite was successfully launched on February 20, 1993. Science observations continued until attitude control of the satellite was lost during a geomagnetic storm on July 14, 2000. ASCA reentered the atmosphere on March 2, 2001 after more than 8 years in orbit.

ASCA’s X-ray telescope mirrors were designed to be optimized for high collecting area with a tight weight constraint. The design team achieved this using an innovative design of conical foil mirrors, which had been previously demonstrated on a 1990 shuttle-based mission called BBXRT (or Broad-Band X-Ray Telescope). ASCA became the first satellite with using this design, and was the first to be able to collect X-rays up to 10 keV.

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.