The Spitzer Space Telescope is executing the ninth year of extended operations beyond its 5.5-year prime mission. The project anticipated a maximum extended mission of about four years when the first mission extension was proposed. The robustness of the observatory hardware and the creativity of the project engineers and scientists in overcoming hurdles to operations has enabled a substantially longer mission lifetime. This has led to more challenges with an aging groundsystem due to resource reductions and decisions made early in the extended mission based on a shorter planned lifetime. We provide an overview of the extended mission phases, challenges met in maintaining and enhancing the science productivity, and what we would have done differently if the extended mission was planned from the start to be nearly twice as long as the prime mission.
Spitzer Warm Mission operations have remained robust and exceptionally efficient since the cryogenic mission ended in
mid-2009. The distance to the onow 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.
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.
The Spitzer Space Telescope launched in August 2003, and has been in its nominal operations phase since December
2003. This paper will review some of the pre-launch, high-level project requirements in light of our operations
experience. We discuss how we addressed some of those requirements pre-launch, what post-launch development we've
done based on our experience, and some recommendations for future missions. Some of the requirements we examine in
this paper are related to observational efficiency, completeness of data return, on-board storage of science data, and
response time for targets of opportunity and data accountability. We also discuss the bearing that mission constraints
have had on our solutions. These constraints include Spitzer's heliocentric orbit and resulting declining telecom
performance, CPU utilization, relatively high data rate for a deep space mission, and use of both on-board RF power
amplifiers, among others.