A table-driven control method to meet continuous, near-real-time observation requirements for the solar X-ray imager

The design of the Solar X-Ray Imager (SXI) for the Geostationary Operational Environmental Satellite (GOES) presented an unusual scenario for controlling the sequence of solar observations. The SXI is an operational instrument, designed not primarily for scientific research, but for providing operational data used by the National Oceanic and Atmospheric Administration (NOAA) to forecast the near-term space weather. To this end, a sequence of images selected to cover the full dynamic range of the Sun will be executed routinely. As the dynamics of the Sun have differing temporal cadences, the frequency of each type of image will vary. These images must be routinely received at the forecast center in near real-time, 24-hours a day, with minimum interruptions. While these requirements clearly lead to a `routine patrol´ of images, the parameters for each do not form a static set. The dynamics of the Sun change with the 11-year solar cycle; the performance of the imaging system will vary with age and on-orbit conditions; and forecasting techniques may change with time. An additional complication is the restricted commanding window and commanding rate. To fulfil these requirements, the SXI is designed to utilize a table-driven approach. Sequences are defined using structured loops, with nested repetitions and delays. These sequences reference combinations of imaging parameters that in turn reference tables of parameters than can be loaded by ground commands. Multiple sequences can be built and stored for later execution. The result is an approach that provides a flexible, yet autonomous SXI capable of meeting arbitrary forecasting requirements and operating within the commanding constraints