Before most Goddard spacecraft components are cleared for launch, they go through final checkups in one of many of the center's clean room facilities. The largest, the High Bay Clean Room, can accommodate two space shuttle payloads at one time.
The High Bay Clean Room, often called the world's largest, prevents dirt, dust and other contaminants from damaging spacecraft components, especially sensitive and carefully calibrated instruments. For example, unlike personal digital cameras, a smudge or speck of dust on the lens of a space telescope is extremely difficult -- if not impossible -- to clean, especially once the spacecraft reaches orbit a few hundred miles up.
A robust ventilation system and an entire wall of air filters help protect against these contaminants. The clean room ventilation system circulates almost one million cubic feet of air every minute through 9,000 square feet of HEPA filters located along one wall. The filters are not your typical off-the-shelf HEPA variety from the local home improvement store. These are specially designed to last several decades.