The National Aeronautics and Space Administration's Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991-2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer's expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/.
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Literally hundreds of people made important contributions to the design and success of the Spitzer mission. A complete list of the participants is presented in Ref. . The authors thank D. Dale and J. D. Smith for providing the spectra of M81 for the cover figure (Fig. ) on behalf of the SINGS legacy team. Portions of the research described here were carried out at the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech) under contract with the National Aeronautics and Space Administration (NASA). The Spitzer Space Telescope is operated by JPL under NASA Contract No. 1407. R.D.G. was supported by NASA through Contract Nos. 1256406 and 1215746 issued by JPL/Caltech to the University of Minnesota. Reference herein to any specific commercial product, process, or service by trade name, trademark, or manufacturer, or otherwise does not constitute or imply its endorsement by the United States Government or JPL/Caltech.