Water Pump Assembly for the International Space Station.

 

This is a heavy structure with many assemblies for the distribution of refrigerating water for the Active Thermal Control of the Columbus Orbital Facility, which constitutes the european modulus of the International Space Station (ISS).

Some components of ISS are already operational. The main structural model is composed by a solid model for each component that is analyzed separately. In a subsequent phase the submodels are converted to substructures that are then assembled to obtain a unique main structure. Columbus will be launched by the Space Shuttle and the type of loads and structural requirements are those imposed by the NASA specifications for the NSTS payloads.

Each component of the water pump assembly was verified for the fail safe condition in which the loads are applied considering the worst case of failure of a support (for example, a screw) in each component. Some components, like the accumulator, are considered as pressure vessels which may be potentially fracture critical items (PFCI). For them a safe life analysis (fracture mechanics) was performed. In brief, the hypothesys is made of the existence of a crack in the structure that could not be detected during non-destructive tests before the launch.

Scope of the analysis is to verify that if fatigue crack propagation happens, it will be stable during the mission even considering the stress corrosion factor. The fatigue analysis takes into account the effective load spectrum derived from the mission profile (acceptance tests, integration, transportation to KSC, STS launch and flight, docking to ISS, ten years on orbit, re-entry). The list has been shortened. Actually each load is subdivided into different load events.