Which observatory/satellite was launched into space first, Hakucho or Chandra X-ray Observatory?
Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space observatory launched on STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2017 .
LEGRI The Low Energy Gamma-Ray Imager (LEGRI) was a payload for the first mission of the Spanish MINISAT platform, and active from 1997 to 2002. The objective of LEGRI was to demonstrate the viability of HgI detectors for space astronomy, providing imaging and spectroscopical capabilities in the 10-100 keV range.