PMBSS is used to holds the telescope's science instruments and also the 18 beryllium mirror-segments. Largest mirror in the telescope called primary mirror (the one starlight will hit first). It is designed to reduce the changes in the shape of the telescope, because when one side is hotter than the other side. The telescope is operated in the cold temperature with a range between -406 and -343 degrees Fahrenheit, the black plane must move less than 98 nanometers, i.e., approximately 1/1,000 the diameter of a human hair.

Even though its size is despite and complex, it is one of the most lightweight precision-alignment and the structure is ever designed and built. It measures roughly 24 ft tall by 19.5 ft wide by more than 11.5 ft deep and weighs only 190kgs (2,180 pounds). It supports a mission payload and instruments that weigh more than 3,150kgs (7,300 pounds).