The Spitzer telescope is a lightweight reflector of Ritchey-Chrétien design. It weighs less than 50 kg and is designed to operate at an extremely low temperature. The telescope has an 85 cm diameter aperture. All of its parts, except for the mirror supports, are made of light-weight beryllium. Beryllium is a very strong material which works well in the construction of infrared space telescopes because it has a low heat capacity at very low temperatures. The telescope is attached to the top of the vapor-cooled cryostat vacuum shell, which keeps the science instruments very cold.
The design philosophy of the telescope assembly is based on the following guidelines:
Maximize the use of materials with a very high stiffness/density ratio, high thermal conductivity, and low cryogenic specific heat.
Build the entire telescope of the same material to prevent thermal expansion mismatch complications, and to make the telescope assembly as dimensionally stable as possible.
Select a configuration that minimizes the size of the major elements of the telescope assembly.
Strive for the simplest possible design to minimize the number of parts, thereby reducing the time and cost for design, fabrication, and integration.