Kinetics and Kinematics for Translational Motions in Microgravity During Parabolic Flight

Stirling L, Willcox K, Ferguson P, Newman D. Kinetics and kinematics for translational motions in microgravity during parabolic flight. Aviat Space Environ Med 2009; 80:522–31.

Introduction: Astronauts soaring through space modules with the grace of birds seems counterintuitive. How do they adapt to the weightless environment? Previous spaceflights have shown that astronauts in orbit adapt their motor strategies to each change in their gravitational environment. During adaptation, performance is degraded and can lead to mission-threatening injuries. If adaptation can occur before a mission, productivity during the mission might improve, minimizing risk. The goal is to combine kinetic and kinematic data to examine translational motions during microgravity adaptations. Methods: Experiments were performed during parabolic flights aboard NASA's C-9. Five subjects used their legs to push off from a sensor, landing on a target 3.96 m (13 ft) away. The sensor quantified the kinetics during contact, while four cameras recorded kinematics during push-off. Joint torques were calculated for a subset of traverses (N = 50) using the forces, moments, and joint angles. Results: During the 149 traverses, the average peak force exerted onto the sensor was 224.6 ± 74.6 N, with peak values ranging between 65.8–461.9 N. Two types of force profiles were observed, some having single, strong peaks (N = 64) and others having multiple, weaker peaks (N = 86). Conclusions: The force data were consistent with values recorded previously in sustained microgravity aboard Mir and the Space Shuttle. A training program for astronauts might be designed to encourage fine-control motions (i.e., multiple, weaker peaks) as these reduce the risk of injury and increase controllability. Additionally, a kinematic and kinetic sensor suite was successfully demonstrated in the weightless environment onboard the C-9 aircraft.