Short answers, pulled from the story.
Orbiting Astronomical Observatory 2, nicknamed Stargazer, was the first successful space telescope. An Atlas-Centaur rocket launched it on the 7th of December 1968 into a nearly circular orbit at about 750 kilometers altitude.
OAO-2 was the first successful space telescope because its predecessor, OAO-1, failed to operate once it reached orbit. OAO-2 collected ultraviolet data on comets, planets, and galaxies.
OAO-2 carried two major instrument sets facing in opposite directions: the Smithsonian Astrophysical Observatory experiment, also called Celescope, and the Wisconsin Experiment Package. Celescope used four 12-inch Schwarzschild telescopes feeding Uvicon detectors, while the Wisconsin package used seven telescopes.
The Wisconsin Experiment Package observed comet Tago-Sato-Kosaka and found it surrounded by a cloud of hydrogen, confirming the comet was largely made of water. The same work detected the 2175-angstrom bump, an increase in ultraviolet absorption that is still not fully explained.
Arthur Code of the University of Wisconsin-Madison supervised construction of the Wisconsin Experiment Package. It observed over 1200 targets in ultraviolet light before the mission ended in early 1973.
The Celescope experiment cataloged 5,068 ultraviolet stars after observing about 10 percent of the sky. Its detectors lost sensitivity over time, and the experiment was turned off in April 1970.