Debris and particulate filtration problems have been persistent during flights on the Space Shuttle Orbiter since STS-6. Analysis of the Orbiter Environmental and Life Support System (ECLSS) indicated that both the volumetric flows and velocities were essentially designed for ventilation, heat removal, and gas blending with minimal consideration for debris removal. The baseline Orbiter filtration system consisted of a single 300 micron filter at the inlet of the cabin fan primarily to protect the cabin fan hardware. This filter was increased to 70 microns and additional filters added after some hardware failures occurred. However, these changes did not clean the environment as expected. An evaluation of the size and type of debris in the cabin air determined that the debris is able to “short-circuit” the cabin filtration system and remains in the cabin air causing the crew discomfort. To correct this situation, a portable fan and filter assembly (Cabin Air Cleaner) was developed to assist in the cleaning and evaluated during the STS-40 Shuttle mission. The crew observed during the flight that the amount of debris in the air was noticeably reduced as compared with previous flight experiences. The Cabin Air Cleaner (CAC) is routinely being flown on all Shuttle missions exceeding 49 crew days.