Overview

The ASCA (ASTRO-D) satellite is a Japanese X-ray astronomy satellite launched on February 20, 1993. It was designed to explore various scientific phenomena in the universe, including understanding the scientific evolution of the cosmos, verifying black holes, identifying sites of particle acceleration in space, determining the distribution and total mass of dark matter, elucidating the mysteries of the Cosmic X-ray Background (CXB) radiation, and studying the evolution of X-ray celestial objects and deep space.

Weighing approximately 420 kg, ASCA was placed into a nearly circular orbit with a periapsis altitude of 525 km, an apoapsis altitude of 615 km, an inclination of 31 degrees, and a period of 96.5 minutes. After launch, ASCA conducted successful observations but became inoperable in July 2000 due to solar activity, and it eventually re-entered the atmosphere and disintegrated on March 2, 2001.

Observation Instruments

Solid-state Imaging Spectrometer (SIS)

The X-ray CCD camera, SIS, operates in “photon mode,” measuring the energy of each individual X-ray photon. This camera is cooled to -70°C using Peltier elements and radiative cooling, enabling observations with the high energy resolution. SIS can detect X-rays across a broad energy range of approximately 0.4 keV to 12 keV.

Gas Imaging Spectrometer (GIS)

The Gas Imaging Spectrometer (GIS) is an improved version of the instrument used on the “Tenma” satellite. GIS has a wider field of view compared to SIS, allowing for extensive observations at once. It uses a proportional counter with gas, measures the energy and arrival position of the X-rays
which induce fluorescence in the gas.
The energy range is from 0.7 keV to 10 keV.

Achievements

ASCA satellite has contributed significantly to the advancement of astrophysics through numerous astronomical discoveries and achievements, including:

1. Understanding the Chemical Evolution of the Universe

   ASCA’s observation data provided new information on the distribution of elements in the universe and their formation processes, particularly clarifying the distribution of elements produced by supernova explosions.

2. Verification of Black Holes

   Through X-ray observations by ASCA, many black hole candidates were observed and confirmed. The behavior of matter around black holes and the patterns of X-ray fluctuations were also analyzed.

3. Dark Matter Research

   ASCA contributed to determining the distribution and total mass of dark matter through X-ray emissions from galaxy clusters. This led to new insights into the structure formation of the universe.

4. Elucidation of Cosmic X-ray Background (CXB) Radiation

   High-precision spectral data of CXB were obtained, and theoretical models regarding its origin were verified. This achievement supported theories related to the evolution of deep space and the formation of large-scale structures.