Computer Aided Design and Graphics Techniques for EVA Analysis 941558

The size and complexity of Space Station has driven the need for an accurate, reliable analytical tool to assess the extravehicular activity (EVA) crew interfaces at the worksite. On previous spacecraft, each worksite was developed and validated through Neutral Buoyancy underwater testing by the crew using mockups. For spacecraft requiring a significant amount of EVA over large areas, like Space Station, the cost of conducting underwater tests for each of the many hundred worksites becomes prohibitive. Therefore, limited testing must be augmented by accurate graphical analysis.
The Unigraphics II, which is the Computer Aided Design (CAD) system for the International Space Station Alpha (ISSA) Product Group 1 design, was selected and developed. It has a major advantage of easy and rapid access to the accurate and updated Space Station design. The design can be rapidly obtained electronically from layouts, detail drawings, assembly drawings or the Electronic Development Fixture (EDF). Also, it allows the structures and mechanical designers to do preliminary worksite layout on the same system they use for design. In addition, several separate models (files) for EVA constraints, support equipment and Extravehicular Mobility Units (EMUs) have been developed so that a particular worksite can be evaluated for access, reach, work envelope and viewing. It lacks some features that other graphics programs such as McDonnell Douglas Human Modeling Systems (MDHMS) have, which are: animation, easy graphics manipulation and built in anthropometric data.
This UGII technique has been developed and refined over several years (>100 worksites analyzed) and has achieved very high correlation to underwater tests results for worksites on the exterior of the truss. The use of this tool has become a routine but still informal part of the design process. Utilization for verification is another goal which will require further correlation testing utilizing neutral buoyancy and other micro gravity simulation techniques to demonstrate adequate accuracy.
The development of an improved graphics computer program to provide refined animation with anthropometric simulation for the EVA crew person is also discussed. An existing shirt-sleeve human task analysis computer program, MDHMS is being modified to permit detailed reach, access and viewing analysis of an EMU suited crew member. The effects of zero gravity and the constraints imposed by the EMU are also addressed.


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