Following the successful dynamic planning and implementation of IRAC Warm Instrument Characterization activities, transition to Spitzer Warm Mission operations has gone smoothly. Operation teams procedures and processes required minimal adaptation and the overall composition of the Mission Operation System retained the same functionality it had during the Cryogenic Mission. While the warm mission scheduling has been simplified because all observations are now being made with a single instrument, several other differences have increased the complexity. The bulk of the observations executed to date have been from ten large Exploration Science programs that, combined, have more complex constraints, more observing requests, and more exo-planet observations with durations of up to 145 hours. Communication with the observatory is also becoming more challenging as the Spitzer DSN antenna allocations have been reduced from two tracking passes per day to a single pass impacting both uplink and downlink activities. While IRAC is now operating with only two channels, the data collection rate is roughly 60% of the four-channel rate leaving a somewhat higher average volume collected between the less frequent passes. Also, the maximum downlink data rate is decreasing as the distance to Spitzer increases requiring longer passes. Nevertheless, with well over 90% of the time spent on science observations, efficiency has equaled or exceeded that achieved during the cryogenic mission.
Spitzer Warm Mission operations have remained robust and exceptionally efficient since the cryogenic mission ended in mid-2009. The distance to the observatory now exceeds 1 AU, making telecommunications increasingly difficult; however, analysis has shown that two-way communication could be maintained through at least 2017 with minimal loss in observing efficiency. The science program continues to emphasize the characterization of exoplanets, time domain studies, and deep surveys, all of which can impose interesting scheduling constraints. Recent changes have significantly improved on-board data compression, which both enables certain high volume observations and reduces Spitzer's demand for competitive Deep Space Network resources.
The primary scheduling requirement for the Spitzer Space Telescope has been to maximize observing efficiency while assuring spacecraft health and safety and meeting all observer-and project-imposed constraints. Scheduling drivers include adhering to the given Deep Space Network (DSN) allocations for all spacecraft communications, managing data volumes so the on-board data storage capacity is not exceeded, scheduling faint and bright objects so latent images do not damage observations, meeting sometimes difficult observational constraints, and maintaining the appropriate operational balance among the three instruments. The remaining flexibility is limited largely to the selection of unconstrained observations and optimizing slews. In a few cases, the project has succeeded in negotiating DSN tracks to accommodate very long observations of transiting planets (up to 52 hours to date with even longer requests anticipated). Observational efficiency has been excellent with approximately 7000 hours of executed science observations per year.
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