Which observatory/satellite was launched into space first, Hakucho or Chandra X-ray Observatory?
Hakucho Hakucho (also known as CORSA-b before launch) was Japan's first X-ray astronomy satellite, developed by the Institute of Space and Aeronautical Science (then a division of the University of Tokyo). It was launched by the ISAS M-3C-4 rocket on February 21, 1979 and reentered the atmosphere on April 16, 1985 .
XEUS XEUS (X-ray Evolving Universe Spectroscopy) was a space observatory plan developed by the European Space Agency as a successor to the successful XMM-Newton X-ray satellite telescope. It was merged to the International X-ray Observatory around 2008, but as that project ran into issues in 2010, the ESA component was forked off into Advanced Telescope for High Energy Astrophysics (ATHENA).