Although it provides an insightful first look at the effect of CG on human performance in lunar gravity, the underwater environment does not permit several critical data parameters such as metabolic rate and biomechanics to be collected. The purpose of this study was to expand on the preliminary CG research from the underwater environments and evaluate the effects of varying CG on human performance in lunar gravity using the Johnson Space Center (JSC) SVMF partial-gravity offload system (POGO) with unsuited subjects.
The primary objective of this study was to evaluate whether and how a change in a system's CG affects human performance metrics (eg, metabolic rate, biomechanics, subjective ratings, stability) in simulated lunar gravity during level-ground ambulation, inclined ambulation, exploration tasks, and postural testing. It should be noted that this objective was to be tested in both the unsuited and the suited condition, but was only tested in the unsuited condition. The POGO, in its current configuration, could not offload the additional weight required to complete the test in the suited condition.
Four different system CG locations were tested during IST-3. The perfect CG was chosen because it represents the ideal condition of adding significant mass to the subject in perfect proportion so that it does not alter the subject’s own CG. The Backback CG was chosen because it represented a potential option based on current suit and Portable Life Support System (PLSS) modeling. The CTSD CG was the CG of the suit. The POGO CG was determined to be the system CG as tested during previous suit tests, including the EWT, IST-1, and IST-2.
Three different offload profiles were used during this study. The first profile involved no offload, with the subjects performing all tasks in 1-g with no CG rig and unconnected to the POGO (1-g). The second profile had the subject don the CG rig at the Perfect CG, but with the weight of the CG rig offloaded so that the subject’s total gravity adjusted weight (TGAW) was the same as the first profile, his 1-g body weight (1-g [Perfect]). TGAW, which is defined as the weight remaining on the ground, is the product of the total system mass and the offload level. The third profile had the subject don the CG rig before the total system mass (combined mass of the subject, gimbal, and CG rig) was offloaded to represent lunar gravity (1/6-g) (Perfect, Backpack, CTSD, POGO).
CG locations for the system CG in relation to the subject and the gimbal axes of rotation were modeled before the test to provide the configuration of the CG rig for each condition, but these locations were based on the standard subject model. To determine how much variation occurred because of varied subject anthropometry, further analysis was performed using each individual subject’s height and weight to modify the standard subject model on completion of the test sessions. Subjects were lined up in a consistent orientation to the gimbal support structure before the CG of the system and the relation of the system CG to the gimbal axes of rotation were recalculated. This recalculation proved valuable for another reason: Three of four CGs were well tolerated, but the CTSD CG was consistently the most difficult for all subjects to cope with. When performing tasks in this CG, many subjects described the feeling as similar to a “horse-collar” tackle in football, with subjects feeling as though they were being pulled down and backwards from the base of the neck. Because these subjects did not experience this with any of the other conditions, the investigative team believed there was an error in the initial model calculations.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|EPSP||01/01/2006||09/30/2010||4 years, 9 months|