MISSION PLANNING

The process of planning a science mission on the space shuttle is a complicated one, especially if ``astronomy" is the science being pursued. The planning process has to include all the constraints intrinsic to the actual observations (e.g., visibilities of the objects from low-earth orbit, brightness of the objects, position relative to the day/night terminator of the orbit [or the sun or the moon], etc.), as well as all the constraints that arise due to the shuttle itself (e.g., propellant available for maneuvers, maneuver rates, thermal constraints, crew cycles, availability of TDRS coverage for communications, etc.). Even though the three UV telescopes are co-aligned, the science goals of each team are sufficiently different from one another that mechanisms are needed to assure that the resources are shared equitably between the teams. In addition, the actual science programs can cause additional constraints (e.g., ephemeris targets, moving targets, or objects that should only be observed in conjunction with another object, etc.).

Pre-mission planning involves planners from the science teams (including Guest Investigators), the Marshall Space Flight Center Mission Operations Laboratory and the Johnson Space Center Mission Operations Directorate. The science teams are responsible for developing a proposed sequence of observations (science plan) that best accomplishes the science goals of the science teams and their Guest Investigators. This involves selecting and prioritizing potential targets for a given launch assumption (based on target visibilities and science priorities) and then actually building the proposed sequence of observations in detail. Subsequent to this, the MSFC planners take the science plan as an input to create the ``attitude timeline"; orbiter maneuvers are designed to accomplish science pointing needs as well as to satisfy various Orbiter and Spacelab needs. In the mean time, the science team members do all of the background work necessary to ensure a proper instrument configuration for the observation. For HUT this includes selecting the appropriate aperture, choosing potential HUT TV guide stars and magnitude settings, finalizing coordinates or any requested roll angles, estimating the expected count rate for each object, and determining whether any special procedures are necessary, either for instrument safety or for special observational requirements (e.g., offsets, variable targets, etc.). When compiled and verified, this information is translated into a form understandable by the instrument and Spacelab computers and loaded onto the Mass Memory Unit (MMU) on the Shuttle.

The following sections will describe many of these steps in more detail, concentrating on the details of observation planning that are specific to HUT observations. The reader is directed to the Mission Planning Handbook and Interface Requirements Document (MPHIRD) for more detailed information on other aspects of mission planning.