Since HUT remains in the shuttle bay for the extent of a mission and relies on the shuttle for power, telemetry, and pointing control, it was designed to be operated much like a modern ground-based telescope rather than a free-flying spacecraft. Just as the telescope operator and the astronomer work together to point a telescope on the ground and operate the attached instrument through computer control, the shuttle crew, the mission specialist (MS), and the payload specialist (PS) maneuver the shuttle, control the instrument pointing system (IPS), and operate HUT with a set of computer terminals aboard the shuttle. There are several different methods of target acquisition and pointing control for the Astro telescopes, which will be described in more detail below, but the basic observing sequence for a target is similar in all cases. After a shuttle maneuver to orient the observatory and an IPS slew to the target, the MS and the PS use the video display from the HUT acquisition TV camera to identify the target and center it in the HUT aperture using manual commands to control the IPS pointing direction. The IPS then normally tracks the guide stars identified in its three star trackers to stabilize the pointing. The instruments are set up in the appropriate configuration for the current target, and the observation is commanded to begin.
While the shuttle crew has primary responsibility for shuttle and instrument control, many of these operations can also be commanded from the Payload Operations Control Center (POCC) at MSFC, and ground control of the instruments was the mode of operation used for the Astro-1 mission after the failure of both data display units (DDU's, the computer terminals) aboard the shuttle. This experience showed that ground commanding actually has many advantages for specific aspects of Astro operations, and operational procedures for Astro-2 are being developed that will combine the best features of crew and ground control.
Ground operations in the POCC also play a significant role in maximizing the scientific return during the Astro missions. More than 80% of the science data from HUT is available in real time in the POCC. These data are analyzed nearly in real time to optimize the configuration of HUT (e.g., optical alignment, focusing, detector performance, etc.) and to evaluate the results of observations. The POCC team replans the science timeline based on these real time results to make sure that the highest priority observations are successfully completed before the end of the mission.
The following sections give more details on specific aspects of mission operations as they relate to HUT.