The instruments of the Spitzer Space Telescope are cooled directly by liquid helium, while the optical system is cooled by helium vapor. The greater the power dissipation into the liquid helium, the more vapor is produced, and the colder the telescope. Observations at shorter wavelengths do not require telescope temperatures as low as those required at longer wavelengths. By varying the telescope temperature with observing wavelength, we are extending the mission lifetime by an estimated 9%.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.