Modeling Space Suit Mobility: Applications to Design and Operations

Abstract

Computer simulation of extravehicular activity (EVA) is increasingly being used in planning and training for EVA. A space suit model is an important, but often overlooked, component of an EVA simulation. Because of the inherent difficulties in collecting angle and torque data for space suit joints in realistic conditions, little data exists on the torques that a space suit's wearer must provide in order to move in the space suit. A joint angle and torque database was compiled on the Extravehicular Maneuvering Unit (EMU), with a novel measurement technique that used both human test subjects and an instrumented robot. Using data collected in the experiment, a hysteresis modeling technique was used to predict EMU joint torques from joint angular positions. The hysteresis model was then applied to EVA operations by mapping out the reach and work envelopes for the EMU.

Modeling and Testing of a Mechanical Counterpressure Bio-Suit System

“…In order to bend their elbows or knees, the astronauts are exerting significant energy to counter the torque of the spacesuit, similar in nature to the constant force needed to hold a balloon in a bent, non-neutral position. The Robotic Space Suit Tester located in the MIT Man Vehicle Lab has measured the torques to be 14.6 N-m to bend the knee 72 degrees and 3.7 N-m to bend the elbow 80 degrees for a flight class III EMU [4]. Therefore, the astronauts become much more tired as they conduct EVAs than they would accomplishing similar activities normally, which places limits on their ability to explore, perform maintenance, or conduct scientific investigations.…”

“…The new requirement is not based on any physiological value, but to reduce by half (approximately) the additional torque created by the EMU to bend the knee 72° [4].…”

“…The average longitudinal radius of curvature is 12.73 cm at 90° [4], so the torque necessary to offset this 9 kPa pressure loss is 17.5 N-m. This is somewhat greater than the 14.6 N-m torque currently caused to move the knee in the EMU to 72° [4], although it should be noted that more torque would be expected for the larger angle. The small difference between the values reveals that pressure could potentially be created in this manner without significant increase in movement difficulty compared to the current spacesuit.…”

“…Therefore, only the generalized results of this research are useful for this particular application, as further investigation is needed to provide data from MCP research that could be applied to EVA opportunities. 4 …”

Investigation of a Cable-Driven Parallel Mechanism for Pressure Suit Arm Resizing and Motion Assistance

“…In a 2001 paper [17], students at the Massachusetts Institute of Technology attempted to quantify the amount of torque required to actuate joints on this suit. The study suggested that the elbow flexion torque (imagine stretching your arm out in front of you, and then curling the lower arm back towards the chest) could exceed 15 N-m (11 ft-lb) at an angle of 105 degrees (at this angle, the lower arm is fifteen degrees past orthogonal from the upper arm).…”