The
Chandra X-ray Observatory (
CXO), previously known as the
Advanced X-ray Astrophysics Facility (
AXAF), is a
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 .