The Space Infrared Telescope Facility (SIRTF), a cryogenic infrared observatory planned for launch around the turn of the century, will span the 3 - 180 micrometers spectral wavelength during its operation in an earth-trailing heliocentric orbit. SIRTF's environmental conditions and mass constraints present challenging requirements to the optical engineer. The SIRTF telescope will operate at near liquid helium temperatures after encountering a launch environment. The Optical Telescope Assembly, which incorporates the primary and secondary mirrors, baffles and support structure, must retain alignment after launch vibration, gravity release and cooldown. Additionally, telescope mass requirements indicate the use of lightweight primary mirror technologies for SIRTF. Candidate primary mirror substrates include fused silica, beryllium, and silicon carbide. Each material has its set of trade-offs. This paper presents these telescope engineering issues and how the SIRTF telescope technology plan addresses them in order to facilitate the final design.