Spitzer Space Telescope, the fourth and final of NASA's Great Observatories, and the cornerstone to NASA's Origins
Program, launched on 25 August 2003 into an Earth-trailing solar orbit to acquire infrared observations from space.
Spitzer has an 85cm diameter beryllium telescope, which operates near absolute zero utilizing a liquid helium cryostat
for cooling the telescope. The helium cryostat though designed for a 2.5 year lifetime, through creative usage now has an
expected lifetime of 5.5 years. Spitzer has completed its in-orbit checkout/science verification phases and the first two
years of nominal operations becoming the first mission to execute astronomical observations from a solar orbit. Spitzer
was designed to probe and explore the universe in the infrared utilizing three state of the art detector arrays providing
imaging, photometry, and spectroscopy over the 3-160 micron wavelength range. Spitzer is achieving major advances in
the study of astrophysical phenomena across the expanses of our universe. Many technology areas critical to future
infrared missions have been successfully demonstrated by Spitzer. These demonstrated technologies include lightweight
cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiation both passive and
active cryogenic cooling of the telescope in space following its warm launch. This paper provides an overview of the
Spitzer mission, telescope, cryostat, instruments, spacecraft, its orbit, operations and project management approach and
related lessons learned.