IMPLEMENTATION OF A MARK III COMPUTATIONAL MODEL TO DECOMPOSE HIP JOINT TORQUES
Harvard-MIT Bioastronautics PhD Candidate
INTRODUCTION: Understanding the overall required joint torques to operate a given suit can enable crew performance predictions. However, it is currently not clear how design changes would affect the total torques. A computational method was used to provide component level contributions to the overall required torque, which can be used to select suit designs that minimize total torque. Here the Mark III Planetary Space Suit (MIII) was examined, which uses a multi-bearing, hip-brief assembly (HBA) that provides mobility through three bearings, each with a single rotational degree of freedom.
METHODS: A computer model of the MIII was built with geometries obtained from external 3D scans and then updated with material properties and pressurized bearing resistances. To validate the model kinetics, the total torque output was compared to existing experimental pressurized benchtop data. After validation, the model was used to decompose the joint torques into the contributing components (due to inertias and bearing resistances), which is not possible experimentally. The model was also used to compare forcing strategies (i.e., motion generated by a force external or internal to the suit).
RESULTS: Model total torque outputs aligned with experimental outputs when compared to the matched external forcing condition (how the HBA was actually forced). External forcing generated increased use of the mid bearing when compared to the internal forcing condition, showing the importance of protocol produces. Adapting speed within the kinematic profiles provided different torque estimates consistent with the bearing resistance profiles.
DISCUSSION: The increased use of the upper bearing and reduced use of the mid bearing for the internal compared to external forcing is driven by the locations of the applied forces. The external force was applied distal to the HBA, activating the mid bearing before the upper bearing. The internal force was applied proximal to the HBA, activating the upper bearing first. In addition to providing insight into suit design parameters, this modeling effort provides the effect of benchtop testing methodology. Experimental procedures may be preferred that more closely align with operational use of the suit to obtain improved estimates of the operator kinetics.
Gen. David Stringer
Director, NASA Plum Brook Station
David L. Stringer is the Director, NASA Plum Brook Station, Sandusky, Ohio since February 18, 12007. The station, 6,400 acres (2400 hectares) include four world-unique test facilities including the largest space test chamber in the world and the only space test chamber capable of firing a rocket engine at altitude. The station’s 100 megawatt power grid with eight substations permits full power generation or consumption with no effect on the civil activities outside the station.
He served in the US Air Force until January 1, 2007, retiring as a Brigadier General. He was the first aircraft maintenance officer assigned to the 4477th Test and Evaluation Squadron which flew three types of Soviet aircraft to prepare American aircrews for combat. He commanded a squadron in England and a group in Italy and his final job was commanding Arnold Engineering Development Center in Tennessee. He was assigned to permanent duties overseas six times for a total of twelve years, including the 1995 air war over Bosnia and the 199 Kosovo war in the Balkans.
He holds a Bachelor of Science in Foreign Service from Georgetown University and a Master of Arts in History from the University of Alabama. He was one of twelve in 1992 selected across the Department of Defense to attend Harvard’s John F. Kennedy School of Government as a National Security Fellow.