We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space
Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month-
long calibration and characterization campaign was conducted. The array temperature and bias setpoints were
revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to
improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500
mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the
same as the cryogenic mission with the 3.6 μm array being slightly less sensitive (10%) and the 4.5 μm array within 5%
of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 μm, and better than
milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the
absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was
conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science
programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the
early universe, and in our understanding of the properties of exoplanets.
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, the fourth and final of NASA's Great Observatories, was launched in August 2003. It has been a major scientific and engineering success, performing science observations at wavelengths ranging from 3.6 to 160 microns, and operating at present with a roughly 92% science duty cycle. This paper describes the essential role and procedures of the Spitzer Observatory Planning and Scheduling Team (OPST) in providing rapid rebuilds of sequences to enable the scheduling of Targets of Opportunity and to recover from anomalies. These procedures have allowed schedulers to reduce the nominal lead time for science inputs from six weeks to 2 or 3 days. We discuss procedures for modifications to sequences both before and after radiation to the spacecraft and lessons learned from their implementation.
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.
Launched as the Space Infrared Telescope Facility (SIRTF) in August, 2003 and renamed in early 2004,
the Spitzer Space Telescope is performing an extended series of science observations at wavelengths ranging from 3
to 180 microns. The California Institute of Technology is the home of the Spitzer Science Center (SSC) and
operates the Science Operations System (SOS), which supports science operations of the Observatory. A key
function supported by the SOS is the long-range planning and short-term scheduling of the Observatory.
This paper describes the role and function of the SSC Observatory Planning and Scheduling Team (OPST), its
operational interfaces, processes, and tools.