The smallest manned spacecraft conceivable is the Extravehicular Activity Space Suit (EVA). It makes the astronaut autonomous on the space facilities, protecting him against the hostile environment and allowing the crew to provide sufficient performance and productivity.
The specificity of the suit enclosure is related to the fact that it must ensure protection functions which are in conflict with the human performance function. For example, the enclosure is pressurized to protect the astronaut against the vacuum but such inner pressure rigidifies limbs and waist thus degrading mobility and working capability.
The mobility is obtained through the combination of pressure tight bearings and one or two degrees of freedom (DOF) joints interfacing with a hard upper torso and hard bearings. In fact, the astronaut (motor) and the suit (passive) can be considered as two separate robots working in parallel, the performance depending on their compatibility and the level of the inner pressure.
This paper is based on the European Space Suit soft joints development and gives a study about the soft joints performances and working behaviour, which is the most important parameter limiting the Suit Enclosure inner pressure and the Zero Prebreath Suits feasibility.
It starts with the identification of design drivers, pointed out in accordance with the top level functional and performance requirements. Such drivers strongly influenced conceptual choices, which were reviewed by test campaigns, thus enabling parametric studies of the most important ones (e. g. torque versus range of motion).
The second part of the paper analyses the torque performances of soft joints as a function of the inner pressure and mobility range for different types of joints, in order to give an assessment about the soft joints used for manufacturing a suit enclosure with an internal overpressure up to 600 hPa.
The third part of the paper analyses the joint behaviour in function of the joint diameter, joint type, etc. and provides an assessment of the historical background, mass and level of available technology.
In the end the paper makes reference to application (PACHA) of the technology developed for EVA Space Suits to the terrestrial human protection against a hostile environment.