ALBERT

Description: The objectives of this study are to show that the characteristics of an intact muscle are different from those of an isolated muscle and to describe a simulation based model. This model, unlike the optimization based models, accounts for the redundancy in the musculoskeletal system in predicting the amount of forces generated within a muscle. The results of this study show that the loading of the primary muscle is increased by the presence of other muscle activities. Hence, the previous models based on optimization techniques may underestimate the severity of the muscle and joint loadings which occur during manual material handling tasks.

Description: The designers of the Orion Crew Exploration Vehicle (CEV) utilize an intensive simulation program in order to predict the launch and landing characteristics of the Crew Impact Attenuation System (CIAS). The CIAS is the energy absorbing strut concept that dampens loads to levels sustainable by the crew during landing and consists of the crew module seat pallet that accommodates four to six seated astronauts. An important parameter required for proper dynamic modeling of the CIAS is knowledge of the suited center of mass (COM) variations within the crew population. Significant center of mass variations across suited crew configurations would amplify the inertial effects of the pallet and potentially create unacceptable crew loading during launch and landing. Established suited, whole-body, and posture-based mass properties were not available due to the uncertainty of the final CEV seat posture and suit hardware configurations. While unsuited segmental center of mass values can be obtained via regression equations from previous studies, building them into a model that was posture dependent with custom anthropometry and integrated suit components proved cumbersome and time consuming. Therefore, the objective of this study was to quantify the effects of posture, suit components, and the expected range of anthropometry on the center of mass of a seated individual. Several elements are required for the COM calculation of a suited human in a seated position: anthropometry; body segment mass; suit component mass; suit component location relative to the body; and joint angles defining the seated posture. Anthropometry and body segment masses used in this study were taken from a selection of three-dimensional human body models, called boundary manikins, which were developed in a previous project. These boundary manikins represent the critical anthropometric dimension extremes for the anticipated astronaut population. Six male manikins and 6 female manikins, representing a subset of the possible maximum and minimum sized crewmembers, were segmented using point-cloud software to create 17 major body segments. The general approach used to calculate the human mass properties was to utilize center of volume outputs from the software for each body segment and apply a homogeneous density function to determine segment mass 3-D coordinates. Suit components, based on the current consensus regarding predicted suit configuration values, were treated as point masses and were positioned using vector mathematics along the body segments based on anthropometry and COM position. A custom MATLAB script then articulates the body segment and suit positions into a selected seated configuration, using joint angles that characterize a standard seated position and a CEV specific seated position. Additional MATLAB(r) scripts are finally used to calculate the composite COM positions in 3-D space for all 12 manikins in both suited and unsuited conditions for both seated configurations. The analysis focused on two aspects: (1) to quantify how much the whole body COM varied from the smallest to largest subject and (2) the impacts of the suit components on the overall COM in each seat configuration. The location across all boundary manikins of the anterior- posterior COM varied by approximately 7cm, the vertical COM varied by approximately 9-10cm, and the mediolateral COM varied by approximately 1.2 cm from the midline sagittal plane for both seat configurations. This variation was surprisingly large given the relative proportionality of the mass distribution of the human body. The suit components caused an anterior shift of the total COM by approximately 2 cm and a shift to the right along the mediolateral axis of 0.4 cm for both seat configurations. When the seat configuration is in the standard posture, the suited vertical COM shifts inferiorly by up to 1 cm whereas in the CEV posture the vertical COM has no appreciable change. These general differences were due the high proportion of suit mass located in the boots and lower legs and their corresponding distance from the body COM as well as the prevalence of suit components on the right side of the body.

Description: Kinematics, the study of motion exclusive of the influences of mass and force, is one of the primary methods used for the analysis of human biomechanical systems as well as other types of mechanical systems. The Anthropometry and Biomechanics Laboratory (ABL) in the Crew Interface Analysis section of the Man-Systems Division performs both human body kinematics as well as mechanical system kinematics using the Ariel Performance Analysis System (APAS). The APAS supports both analysis of analog signals (e.g. force plate data collection) as well as digitization and analysis of video data. The current evaluations address several methodology issues concerning the accuracy of the kinematic data collection and analysis used in the ABL. This document describes a series of evaluations performed to gain quantitative data pertaining to position and constant angular velocity movements under several operating conditions. Two-dimensional as well as three-dimensional data collection and analyses were completed in a controlled laboratory environment using typical hardware setups. In addition, an evaluation was performed to evaluate the accuracy impact due to a single axis camera offset. Segment length and positional data exhibited errors within 3 percent when using three-dimensional analysis and yielded errors within 8 percent through two-dimensional analysis (Direct Linear Software). Peak angular velocities displayed errors within 6 percent through three-dimensional analyses and exhibited errors of 12 percent when using two-dimensional analysis (Direct Linear Software). The specific results from this series of evaluations and their impacts on the methodology issues of kinematic data collection and analyses are presented in detail. The accuracy levels observed in these evaluations are also presented.

Description: Suited human performance studies in reduced gravity environments to date include limited observations from Apollo Lunar surface Extravehicular Activities (EVA) and from previous studies conducted in partial gravity simulation environments. The Constellation Program EVA Systems Project office has initiated tests to develop design requirements for the next generation Lunar EVA suit. Theses studies were conducted in the Space Vehicle Mock-Up Facility (SVMF) at Johnson Space Center from which the results provided recommendations for suit weight, mass, center of gravity, pressure, and suit kinematic constraints that optimize human performance in partial gravity environments.

Description: Astronauts have the task of retrieving and deploying satellites and handling massive objects in a around the payload bay. Concerns were raised that manual handling of such massive objects might induce loads to the shuttle suits exceeding the design-certified loads. The Crew and Thermal Division of NASA JSC simulated the satellite handling tasks (Satellite Manload Tests 1 and 3) and determined the maximum possible load that a suited member could impart onto the suit. In addition, the tests revealed that the load to the suit by an astronaut could be calculated from the astronaut's maximum hand grasp breakaway strength. Thus, this study was conducted to document that hand grasp breakaway strengths of the astronauts who were scheduled to perform EVA during the upcoming missions. In addition, this study verified whether the SML 3 test results were sufficient for documenting the maximum possible load. An attempt was made to predict grasp strength from grip strength and hand anthropometry. Based on the results from this study, the SML 3 test results were deemed sufficient to document the maximum possible load on the suit. Finally, prediction of grasp strength from grip strength was not as accurate as expected. Hence, it was recommended that grasp strength be collected from the astronauts in order to obtain accurate load estimation.

Description: The Anthropometry and Biomechanics Laboratory at the Johnson Space Center has been collecting anthropometric data from astronaut applicants since 1977. These anthropometric measurements had been taken from 473 applicants. Based on the position they applied for, these applicants were classified as either mission specialists, payload specialists, pilots, or observers. The main objective was to document the variations among these applicants and tabulate the percentile data for each anthropometric dimension. The percentile and the descriptive statistics data were tabulated and graphed for the whole astronaut candidate population; for the male and female groups; for each subject classification such as pilot, mission specialist, and payload specialist; and finally, for those who were selected as astronauts.

Description: One of the concerns of Space Station designers was making sure that the suited crewmembers' gloved fingers are not trapped in the holes that may be present in the structures during EVA activities. A study was conducted on 11 subjects to determine the minimum and maximum possible hole sizes that would eliminate the possibility of finger entrapment. Subjects wore pressurized gloves and attempted to insert their fingers into holes of various sizes. Based on the experimental results, it is recommended that the smallest diameter should be less than 13.0 mm and the largest diameter should be greater than 35.0 mm in order to eliminate the possibility of finger entrapment while wearing gloves. It is also recommended that the current requirements specified by the MSIS-STD-3000 (Section 6.3.3.4) should be modified accordingly.

Description: The STS-61 Shuttle mission, which took place in December 1993, was solely aimed at servicing the Hubble Space Telescope (HST). Successful completion of this mission was critical to NASA since it was necessary to rectify a flaw in the HST mirror. In addition, NASA had never scheduled a mission with such a high quantity of complex extravehicular activity. To meet the challenge of this mission, the STS-61 crew trained extensively in the Weightless Environment Test Facility at the Johnson Space Center and in the Neutral Buoyancy Simulator at the Marshall Space Flight Center. However, it was suspected that neutral buoyancy training might induce negative training by virtue of the viscous damping effect present in water. The mockups built for this training also did not have the mass properties of the actual orbital replacement units (ORUs). It was felt that the crew should be further trained on mockups with similar mass characteristics. A comprehensive study was designed to address these issues. The study was quantitative, and instrumentation was set up to measure and quantify the forces and moments experienced during ORU mass handling and remote manipulator system run conditions.

Description: One of the reasons for reduction in performance when gloves are donned is the lack of tactile sensitivity. It was argued that grasping force for a weight to be grasped will be a function of the weight to be lifted and the hand conditions. It was further reasoned that the differences in grasping force for various hand conditions will be a correlate of the tactile sensitivity of the corresponding hand conditions. The objective of this experiment, therefore, was to determine the effects of glove type, pressure, and weight of load on the initial grasping force and stable grasping force. It was hypothesized that when a person grasps an object, he/she grasps very firmly initially and then releases the grasp slightly after realizing what force is needed to maintain a steady grasp. This would seem to be particularly true when a person is wearing a glove and has lost some tactile sensitivity and force feedback during the grasp. Therefore, the ratio of initial force and stable force and the stable force itself would represent the amount of tactile adjustment that is made when picking up an object, and this adjustment should vary with the use of gloves. A dynamometer was fabricated to measure the grasping force; the tests were performed inside a glove box. Four female and four male subjects participated in the study, which measured the effects of four variables: load effect, gender effect, glove type, and pressure variance. The only significant effects on the peak and stable force were caused by gender and the weight of the load lifted. Neither gloves nor pressure altered these forces when compared to a bare-handed condition, as was suspected before the test. It is possible that gloves facilitate in holding due to coefficient of friction while they deter in peak grasp strength.

Description: With an increase in the frequency of extravehicular activities (EVA's) aboard the Space Shuttle, NASA is interested in determining the capabilities of suited astronauts while performing manual tasks during an EVA, in particular the situations in which portable foot restraints are not used to stabilize the astronauts. Efforts were made to document the forces that are transmitted to spacecraft while pushing and pulling an object as well as while operating a standard wrench and an automatic power tool. The six subjects studied aboard the KC-135 reduced gravity aircraft were asked to exert a maximum torque and to maintain a constant level of torque with a wrench, to push and pull an EVA handrail, and to operate a Hubble Space Telescope (HST) power tool. The results give an estimate of the forces and moments that an operator will transmit to the handrail as well as to the supporting structure. In general, it was more effective to use the tool inwardly toward the body rather than away from the body. There were no differences in terms of strength capabilities between right and left hands. The power tool was difficult to use. It is suggested that ergonomic redesigning of the power tool may increase the efficiency of power tool use.