The lower deck contains environmental control systems and storage facilities. Pressurization can be controlled from inside the airlock or mid-deck. Some 25-50 tiles are now replaced after each mission. Two main 11,000 rpm fans circulate air in five major loops. A 147 kg Regenerative CO 2 Removal System is carried by the EDOs.
Air is cooled after flowing through the filters by four heat exchangers.
These are part of two parallel water coolant loops. The warmed water is pumped to a cargo bay Freon-21 heat exchanger as part of the main thermal control system. For 16-day EDO missions a cryogenic pallet is carried in the aft cargo bay. The 2,926 kg pallet plumbs four tank sets to the current five. Improved APUs were introduced on OV-105 and retrofitted to the others.