Research equipment on the ISS will be housed in racks, as it was on the space shuttle. For the ISS, there are two kinds of racks: EXPRESS (Expedite the Processing of Experiments to Space Station) racks and ISPR (International Standard Payload Rack). ISPRs are the basic housing within the various modules (U.S., Japanese, Russian, etc.) that make up the ISS. ISPRs can then be fitted with specialized racks designed to support specific projects or research areas; the planned Biotechnology Facility (BTF) is one such rack. Alternatively, the EXPRESS racks, which are generic experiment support structures, can be fitted into the ISPR. The EXPRESS rack has subsystems for providing experiments with necessary resources such as power, water, vacuum, and gases. The standard EXPRESS rack holds eight middeck locker equivalents (MLEs) and two drawers (for storage). MLEs are the standard unit for hardware volume on the space shuttle and the ISS, and even within customized racks, such as the BTF, experimental hardware will still consist of modular MLE units. Each MLE is 20 by 16 by 11 in., and the modular equipment that fits in the MLE can weigh approximately 60 to 70 lb. The racks are located within the cylindrical modules that make up the ISS; the hardware described below under development by NASA is all currently scheduled to be placed in the Japanese Experiment Module.
Thermal Enclosure System (TES) and Single Locker Thermal Enclosure System (STES). The TES (which takes up two MLEs) and the STES (which takes up one MLE) are refrigeration and incubation modules whose internal volume temperature can be controlled to any set temperature between 4°C and 40°C. The stability of the set temperature is ±0.5°C for the STES and ±0.2°C for the TES. The thermal control is accomplished by the conduction of heat in or out of the internal enclosure through a side wall. Science hardware for biotechnology investigations can be flown inside the TES or the STES, and both systems were used to transport and house space crystallization devices during previous spaceflights. Science hardware currently flown within the TES/STES includes the DCAM, PCAM, VDAs, OPCGA, and DCPCG (see below for descriptions), as well as any new experiments requiring thermal control.
Biotechnology Ambient Generic (BAG). The BAG terminology is used to describe any flight of DCAM, PCAM, or VDA-2 hardware as stowage items subject to ambient Orbiter or ISS conditions rather than the thermally controlled environment of a TES or STES. The functionality of the DCAM, PCAM, and VDA-2 hardware is identical to its functionality when flown in an enclosure. However, the number of DCAM trays, PCAM cylinders, or VDA-2 trays flown may vary owing to differences in the ambient stowage volume. A temperature data logger is flown in conjunction with any BAG payload.