The Astro-2 mission began at UT 06:38:13 on 1995 March 2 with the launch of the space shuttle Endeavour (STS-67). The orbit was nearly circular at an altitude of 352 km and an inclination of 28.5 . Instrument activation started at Mission Elapsed Time (MET), and first light occurred at MET with an observation of Capella. Science operations began at MET, and continued with only minor interruptions until the instruments were deactivated at MET. Observing efficiency was low during the first day of science operations while the target acquisition and tracking procedures were refined, but was in accordance with pre-mission expectations thereafter. Pointing stability was frequently as good as RMS, though the absolute pointing error could be several arcseconds. The performance of HUT itself was nominal in nearly all respects throughout the flight, with two significant exceptions: a discrepancy between the best focus for the camera and spectrograph, and a gradual decrease in the instrument throughput during the flight, which are discussed in detail below.