In the frame of the development of the European EVA Suit, a complete trade-off was conducted to select the lower torso architecture. This study, performed under an ESA contract, included a formal trade-off dealing with all cost and programmatic impacts together with a technical assessment based on man rated underwater evaluations and analysis.
The candidate architectures were: the European baseline including 2 hip and 2 thigh bearings, the Russian like soft ORLAN-DMA, a soft lower torso including 2 thigh bearings and another soft one including 2 calf bearings.
The idea was to compare the different design performances without having necessarily developed the 4 pressurized lower torsos and then also to gain experience on predicting methods for such ergonomic/kinematic studies.
The trade-off was based on the manned underwater evaluation of ergonomical suit simulators (wet suit concept), supported by the 1-g pressurized evaluation of the Russian ORLAN-DMA and CAD-CAM kinematic analysis.
The test campaign in neutral buoyancy was conducted on a modular “wet suit” allowing to simulate the different suit architectures, and adjustable over all the required anthropometric range. For each concept and for the 3 divers representing the extremes and the mean case of the population, the evaluations included “EVA reference tasks” to assess the intrinsic architectures performances and “operational capability” determination to approach the architectures efficiency in front of a simplified EVA activity.
The supporting manned evaluation performed by ZVEZDA assessed the waist rotation provided by a pressurized ORLAN type suit with and without hip bearings, for different suit adjustments.
A set of analysis were conducted on CATIA CAD-CAM to predict all the test results and were used to correlate the theoretical kinematic models with the experienced suit performances.
These evaluations demonstrated that the European configuration provided more torso rotation, squatting capability and general mobility than the other concepts but also that, with regards to its mass and complexity, the soft trousers with thigh bearings (or calf bearings) were a good compromize to perform the expected EVA tasks, especially because they provided acceptable waist rotation.
Furthermore, the pressurized tests, the wet suits evaluations in neutral buoyancy and the CATIA predictions turned out to be well correlated and allowed to extrapolate the torque and rotation range of a suit with calf bearings that had not been tested.
The results of this campaign were the selection of a lower torso including calf bearings only, as the new European/Russian baseline and the refinement of the ergonomical/kinematic methodology allowing to theoretically predict the performances of a given EVA architecture.