Each of the eight (8) EXPRESS facilities can support ten (10) small payloads resulting in a total capability to operate 80 experiments. 8 of these positions are the size of a shuttle Middeck Locker: carrying capacity, 72 lbs; internal volume, 2 ft3. The remaining 2 positions are International Subrack Interface Standard (ISIS) drawers: carrying capacity, 44 lbs; internal volume, 1.3 ft3.
With standardized hardware interfaces and streamlined approach, the EXPRESS facilities enable quick, simple integration of multiple payloads aboard the International Space Station (ISS). The system is comprised of elements that remain on ISS, as well as elements that travel back and forth between ISS and Earth via the Space Shuttle. The facilities remain on orbit continually. Experiments are exchanged as needed, remaining on ISS for one month to several years, depending on the experiment's time requirements.
Payloads within any EXPRESS facility can operate independently of one another, allowing for differences in temperature, power levels and schedules. These facilities provide stowage, power, data, command and control, video, water cooling, air cooling, vacuum exhaust, and nitrogen supplies to payloads. Each facility is housed in an International Standard Payload Rack (ISPR), a refrigerator-size container that acts as the facility’s exterior shell.
Experiments in these facilities may be controlled by the crew or remotely by the Payload Rack Officer (PRO) on-duty at the Payload Operations and Integration Center at Marshall Space Flight Center in Huntsville, AL. Linked by computer to all payload racks aboard the Space Station, the PRO routinely checks rack integrity, temperature control and the proper working conditions of the experiments.