Actively controlled mock-ups for EVA training in neutral buoyancy

The drive for more accurate and easily “reconfigurable” extra-vehicular activity (EVA) simulation has spawned the development of “robotic” payloads for use in microgravity simulation. This paper describes work in progress at the University of Maryland to develop actively controlled mock-ups for EVA training in neutral buoyancy. The strengths and weaknesses of parallel mechanism designs, such as the Charlotte IVA robot flown aboard the orbiter, are compared with more commonly available manipulators used in industry. Preliminary experiments performed on a Ranger manipulator arm validate the feasibility of the controls approach being considered. Simulation results are encouraging even for payload masses as low as 125 kg and force loop rates of 40 Hz. Design trade-offs indicate a Charlotte derivative to have many advantages, particularly in the size of workplace and the stiffness of the assembly. A joint industrial effort has been proposed to build a neutral buoyancy version and preliminary designs are currently in progress