In order to extend the Shuttle Orbiter's capability to remain docked to the International Space Station (ISS), a plan was developed that would conserve key consumables, most notably cryogenic oxygen which is used by the Orbiter Fuel Cells (FCs) to produce power. A significant part of the power reduction plan is to eliminate the use of the Orbiter's Booster Fan.
To accomplish air exchange between the ISS and Orbiter, a series of fans are used which include the ISS U.S. Lab (USL)/Pressurized Mating Adaptor (PMA) Intermodule Ventilation (IMV) Fan, the Orbiter Booster Fan, and a portion of the capability provided by the Orbiter Cabin Fan. The elimination of the Booster Fan from the series was predicted to reduce the air exchange significantly, but to not cause any adverse Environmental Control and Life Support (ECLS) conditions in either the Orbiter or ISS.
This reduction in air exchange affects the ability of the ISS to control Orbiter and ISS carbon dioxide, as well as affecting the relative contributions of the Orbiter and ISS in controlling humidity. The latter affects the ability of the ISS to manage condensate water. Because the Russians do not process condensate from the USL, the air exchange reduction could affect ISS planning and water balances.
A Station Development Test Objective (SDTO) was performed on STS-114 to determine if the Booster Fan could be successfully bypassed while maintaining an adequate Orbiter/ISS air exchange rate, and to determine the impact on carbon dioxide and humidity control. Flight data obtained from STS-114 was analyzed to determine how these impacts will affect future Orbiter/ISS missions.