Stephen J. Barba, Lisa J. Garcia, Douglas B. McElroy, David S. Mittman, JoAnn C. O’Linger, and Steven R.Tyler Spitzer Science Center California Institute of Technology Pasadena, CA 91125 626-395-8799 sjb@ipac.caltech.edu , lisag@ipac.caltech.edu , dmcelroy@ipac.caltech.edu , dmittman@ipac.caltech.edu , joanno@ipac.caltech.edu , styler@ipac.caltech.edu Abstract —Launched as the Space Infrared Telescope Facility (SIR TF) 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. 1. INTRODUCTION The Spitzer Space Telescope is the fourth and final of NASA's great observatories, designed to take images and spectra of a wide range of astronomical objects in the infrared - wavelengths of 3 to 180 microns. Spitzer (Figure 1) consists of a spacecraft, an 0.85-meter telescope and three cryogenically-cooled science instruments; the Infrared Array Camera (IRAC), the Infrared Spect rograph (IRS), and the Multiband Imagin g Photometer for Spitzer (MIPS). Launched from Cape Canaveral, Florida, on August 25, 2003, the mission had planned for a 60 day In-Orbit Checkout (IOC) period followed by a 30 day Science Verification (SV) phase. Spitzer employed an innovative warm launch architecture; the telescope is located outside the cryostat and was at ambient temperature at Launch; the telescope is cooled by He vented from the cryostat, and it was cooled to ~5.6 degrees Kelvin over 45 days. At the completion of SV, Spitzer transitioned into its no rmal operating mode, and will have completed twenty-eight months of routine operations as of May 2006. Spitzer’s th ree science instruments are operated in a discrete number of observing modes (7 specified at launch) which are char acterized as Astronomical Ob servation Templates (AOTs). In order to design an observation, the astronomer chooses a template and specifies a number of parameters that are specific to it. These inputs produce a complete recipe for the commandi ng needed to carry out the observation on board Spitzer. The resulting fully-specified observation is called an Astronomical Obse rvation Request (AOR) and the parameters are stored in the Spitzer Science Operations Database (SODB) at the SSC along with estimates of the duration of the observation, the volume of data it will ge nerate, etc. The AORs and their resource estimates become the fundamental inputs to the Planning and Scheduling process.