The process of developing a Payload Attach System (PAS) which will support a wide range of experimental and commercial payloads on the International Space Station (ISS) has experienced an interesting evolution during its design, development, test and evaluation (DDT&E) phase. This evolution has been caused in large measure by requirements intended to insure compatibility of the PAS with the extravehicular activity (EVA) crewmember during nominal and contingency operations in and around the PAS sites. As the design of the ISS transitioned from its Freedom predecessor, the effort to keep costs down by preserving as much of the original Freedom design as possible led to design decisions that challenged engineering thinking. In particular, the decision to preserve the P3 and S3 Pre-Integrated Truss (PIT) segments in their original design configuration presented a challenge to reconcile the Freedom Propulsion Module Attach Structure (PMAS) design with ISS EVA and Attached Payloads requirements.
This paper examines the influence of EVA requirements on the evolution of the PAS design, and the role played by the different EVA analysis tools used by Boeing Extravehicular and Crew Systems (EV&CS) personnel for developing PAS verification activities. Planned PAS verification activities are presented, as are results of analyses and test activities, including neutral buoyancy laboratory (NBL) and human thermal vacuum (HTV) testing at NASA’s Johnson Space Center (JSC). In addition, this paper considers several proposed uses of the PAS design in secondary sites throughout the ISS structure, such as the Spares Warehouse and the Z1 Truss Unpressurized Logistics Carrier Attach System (Z1-ULC-AS).