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The Space Station Freedom (SSF) airlock Depressurization/Repressurization (D/R) subsystem designed by McDonnell Douglas Aerospace Space Station Division is used to depressurize the airlock to allow egress from SSF by two pressure suited crewmembers to perform extravehicular activity (EVA), and to repressurize the airlock at the conclusion of EVA. The D/R subsystem utilizes vacuum, or D/R Equalization (D/RE), lines to accomplish the functions of venting airlock gas to space during depressurization and equalizing pressures between airlock and SSF chambers during repressurization. Categories of D/RE line requirements include performance; safety, reliability, and maintainability; and control and operations. For the development of the SSF airlock, McDonnell Douglas Aerospace has performed analysis and developed design solutions that meet these requirements while optimizing performance and cost. This paper will describe results of this analysis, including system performance data.

This paper will discuss the airlock depress/repress (D/R) system under design by McDonnell Douglas Space Systems Company as part of the Work Package 2 (WP-02) portion of the NASA Space Station Freedom (SSF) program. Requirements for the airlock to support 52 extravehicular activities (EVA) per year have driven several design features which make this system unique from any used on Orbiter, Skylab, or Mir. Use of the airlock to support 52 EVAs per year is a part of the program's overall attempt to make life and work in space a routine endeavor. As a result of this goal, system design must minimize time and resources required to support EVA while maximizing system maintainability, safety, reliability, and usability. Requirements aimed at realizing this design goal are found in JSC 31000 Volume 3, “Space Station Projects Description and Requirements Document,” Revision H (Reference 3). The D/R System must minimize EVA time by depressurizing the airlock within 10 minutes.