What space telescope did STS-93 deploy in 1999?

STS-93 deployed the Chandra X-ray Observatory in 1999.

Launched aboard Space Shuttle Columbia on July 23, 1999, STS-93 had the primary task of releasing Chandra with an Inertial Upper Stage booster. The observatory was originally called the Advanced X-ray Astrophysics Facility before launch.

Chandra studies X-rays from extremely energetic regions, including supernova remnants, black-hole environments, galaxy clusters, and the hot gas around exploding stars. Because Earth's atmosphere blocks most cosmic X-rays, the telescope operates in space, in a highly elliptical orbit reached after deployment.

A common mix-up is confusing Chandra with Hubble. Hubble observes mainly visible, ultraviolet, and some near-infrared light, while Chandra is dedicated to X-ray astronomy. STS-93 was also notable because Eileen Collins became the first woman to command a Space Shuttle mission, and Chandra was the heaviest payload the Shuttle had carried at that time.