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.
NASA's SpitzerSpaceOps Conferences 2 observational capabilities remain either undiminished or improved, and the high overall science data collection efficiency remains nearly unchanged. In this contribution, we outline several operational changes, innovations, and optimizations that have both minimized the impact of the growing distance on data transmission and enhanced the precision of data acquired by the science instruments.Though faced with diminishing budgetary resources that reduced staffing and allowed fewer upgrades of aging equipment, extended mission operations can provide an opportunity to acquire extensive science at bargain prices. The spacecraft, ground, and mission operations systems and procedures to perform the extended mission are already in place from the prime mission. The key to maintaining successful extended operations is the proper automation, modification and process enhancement of extant prime mission capabilities and procedures to maximize science return with acceptable risk as opposed to the creation of new capabilities. Spitzer's successful optimization of existing operational capabilities and the associated lessons learned that have gone into maximizing the lifetime well into its second decade of operation will hopefully provide guidelines for future missions, as it continues to make important contributions to the field of astrophysics, including the recent, highly significant discovery and characterization of exoplanets in the TRAPPIST-1 system.
The Spitzer Space Telescope has a two-phase downlink system. Data are transmitted during one telecom session. Then commands are sent during the next session to delete those data that were received and to retransmit those data that were missed. We must build sequences that are as efficient as possible to make the best use of our finite supply of liquid helium, One way to improve efficiency is to use only the minimum time needed during telecom sessions to transmit the predicted volume of data. But, we must also not fill the onboard storage and must allow enough time margin to retransmit missed data. We describe tools and procedures that allow us to build observatory sequences that are single-fault tolerant in this regard and that allow us to recover quickly and safely from anomalies that affect the receipt or acknowledgment of data.
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.
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