Characterization of Human and Spacesuit Joint Deviations from Body-Worn Inertial Measurement Units

Space suits are designed and tested to support humans and work in the vacuum of space and extraplanetary surfaces. In order to inform this design, engineers must understand relevant work environments and human kinematics the suit must support. This paper demonstrates the usage of body-worn inertial measurement units (IMUs) to inform suit design parameters, specifically: suit joint cycles per hour requirement specification and suit hard bearing lifespan modeling. From IMU-estimated human joint angles for the elbow, hip, and knee, this paper proposes (1) a definition of joint deviation with operational relevance to quantifying suited joint cycles and (2) a model of suit bearing degradation over time based on Lundberg-Palmgren theory. These proposed concepts are demonstrated using a single subject equipped with a set of body-worn IMUs performing a 96 minute long terrestrial fieldwork task-an analog to future extraplanetary science. Results suggest that historical joint cycles/hour requirements (e.g., AX-5 space suit) may be insufficient to capture the full scope of kinematics of planetary fieldwork. Domain experts should consider the level of joint deviation magnitude that is relevant to a designed mission profile. The novel modeling of suit joint rotation and bearing degradation from IMU-based measurements demonstrate an extensible framework to inform future suit design and suited operations evaluation. The use of wearable IMUs has the potential to provide new information for assessing both the operator and the suit through informing physical work demands, mobility requirements, and operations planning.