Observing with HST IV: Improvements in Observation Planning and Scheduling

Planning and scheduling Hubble Space Telescope observations is a formidable task. During the course of a year tens of thousands of exposures are taken on several thousand targets. Many observations are linked to others via scientific ``special requirements'' specified by the observer in the proposal. All observations are subject to numerous observing constraints such as Sun avoidance, occultation by the Earth, and spacecraft roll and power constraints. At the beginning of the HST mission, planning and scheduling work concentrated on the correct implementation and execution of observations. In Cycles 2 and 3 a major effort to increase the productivity of the observatory (while retaining quality) was begun and increased HST observation efficiency by about 50%. In Cycle 4, a major effort is underway to further improve the planning and scheduling process, in order to achieve stability in the observing program long-range plan, to improve the system's flexibility and responsiveness to change, and to increase visibility into the HST observing schedule as it evolves. This paper will describe the basis for these improvements, including the long-range planning criteria and timescales, the process of planning and scheduling and how changes will be supported. We will also describe the major observing constraints and how they are handled by the planning and scheduling system. Finally, we will discuss how recent advances in networking technology have made it possible to dramatically increase the ability of HST proposers to view the long- and short-range HST observing plans. Using a client program such as Mosaic or Lynx, an astronomer will be able to access a World Wide Web (WWW) server at the STScI to provide convenient access to HST observing proposals and their implementation status, and both the long-range and short-term observing schedules