Chandra X-Ray Observatory (CXO):Overview
  The Chandra X-Ray Observatory (CXO), the x-ray component of NASA's Great Observatories, was launched early in the morning of 1999, July 23 by the Space Shuttle Columbia. The Shuttle launch was only the first step in placing the observatory in orbit. After release from the cargo bay, the Inertial Upper Stage performed two firings, and separated from the observatory as planned. Finally, after five firings of Chandra's own Integral Propulsion System--- the last of which took place 15 days after launch--- the observatory was placed in its highly elliptical orbit of 140,000 km apogee and 10,000 km perigee. After activation, the first x-rays focussed by the telescope were observed on 1999, August 12. Beginning with these initial observations one could see that the telescope had survived the launch environment and was operating as expected. The month following the opening of the sunshade door was spent adjusting the focus for each set of instrument configurations, determining the optical axis, calibrating the star camera, establishing the relative response functions, determining energy scales, and taking a series of "publicity" images. Each observation proved to be far more revealing than was expected. Finally, and despite an initial surprise and setback due to the discovery that the Chandra x-ray telescope was far more efficient for concentrating low-energy protons than had been anticipated, the observatory is performing well and is returning superb scientific data. Together with other space observatories, most notably the recently activated XMM-Newton, it is clear that we are entering a new era of discovery in high-energy astrophysics. 
M. C. Weisskopf, H. D. Tananbaum, L. P. Van Speybroeck, and S. L.   O'Dell