Spitzer's model for dealing with the end of the cryogenic mission

The Spitzer Space Telescope is a cryogenically cooled telescope operating three instruments in wavelengths ranging from 3.6 microns to 160 microns. Spitzer, the last of NASA's Great Observatories, was launched in August 2003 and has been operating for 4.5 years of an expected 5.5 year cryogen mission. The highly efficient Observatory has provided NASA and the science community with unprecedented data on galaxies, star formation, interstellar medium, exoplanets, and other fundamental astronomical topics. Spitzer's helium lifetime is predicted to end on April 18, 2009, with an uncertainty of +/- 3 months. Planning for this cryogen end involves many diverse areas of the project and is complicated due to the uncertainty in the actual date of helium depletion. This paper will describe how the Spitzer team is accommodating the unknown end date in the areas of observation selection, planning and scheduling, spacecraft and instrument monitoring, data processing and archiving, and finally, budgeting and staffing. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration.