The Constellation Program (CxP) extravehicular activity (EVA) Systems Project Office (ESPO), which is developing design requirements for the next-generation lunar EVA suit, initiated a series of tests, working with the EVA Physiology, Systems, and Performance (EPSP) Project and the Anthropometry and Biomechanics Facility (ABF) aimed at understanding human performance and suit kinematics under a variety of simulated lunar EVA conditions. These studies included matched unsuited controls in an attempt to identify the specific metabolic costs and biomechanics of the prototype Mark III Advanced Spacesuit Technology Demonstrator (MKIII). A primary goal of the overall test series is to provide evidence-based recommendations for suit mass, center of gravity (CG), pressure, and suit kinematic constraints that optimize human performance in partial gravity environments. Results of this test series will also be combined with studies in other lunar analogs to evaluate the effectiveness and limitations of these environments.
This study, Integrated Suit Test-2 (IST-2), was conducted in the Space Vehicle Mock-up Facility (SVMF) at the Johnson Space Center (JSC) using the MKIII suit because the MKIII is the only planetary suit prototype in NASA’s inventory that is compatible with the partial-gravity simulator, nicknamed POGO. The MKIII also has the most variable operational pressure range of the available prototype suits. IST-2, the companion test to IST-1 (2), had identical objectives and similar test conditions but different test points. Whereas IST-1 focused on level-ground ambulation, IST-2 focused on exploration tasks and inclined ambulation.
The purpose of IST-2 was to move beyond level-ground locomotion and evaluate suited human performance during exploration-type tasks and inclined locomotion. Specifically, the primary objectives of this test were:
- Identify the individual contributions of weight, mass, pressure, and suit kinematics to the overall metabolic cost of the MKIII suit in its 121-kg (265-lb.) POGO configuration, including the mass of the Portable Life Support System (PLSS) mock-up and gimbal, which is 29.6 kPa (4.3 psi) during inclined ambulation and exploration tasks in 1/6-g.
- Quantify the effects of the following factors on suited and/or unsuited metabolic rate, biomechanics, and subjective ratings during exploration tasks and inclined ambulation:
a. Suited – varied suit pressure at constant offload, mass, and CG
b. Suited – varied suit offload (weight) at constant pressure, mass, and CG
c. Unsuited – varied offload (weight) at constant mass and CG
d. Unsuited – varied mass at constant offload and CG
- Compare the MKIII at POGO configuration to the MKIII at POGO configuration with the waist bearing locked.
- Develop predictive models of metabolic rate, subjective ratings, and suit kinematics based on measurable suit, task, and subject parameters.
The secondary objectives of IST-2 did not determine the test protocol. Rather, they are other expected ways for which these data could be applied. They include the following:
- Define standard measures and protocols for objectively evaluating future exploration suit candidates and requirements verification of the flight suit.
- Understand specific human performance limitations of the suit compared to matched shirtsleeve controls.
- Collect metabolic and ground-reaction force data to develop an EVA simulator for use on future prebreathe protocol verification tests.
- Provide data to estimate consumables usage for input to suit and PLSS design.
- Assess the cardiovascular and resistance exercise associated with partial-gravity EVA for planning appropriate exploration exercise countermeasures.
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Subjects were recruited from two different pools of personnel – those who typically perform EVA suited studies for the JSC Engineering Directorate and a group of astronauts, many of whom have previous in-space EVA experience, selected to support exploration EVA studies. Suit fit-checks in the MKIII suit were performed on a range of subjects, and only those who had good suit fit were considered for inclusion in this study due to potential medical and safety issues. From this list, six male astronaut subjects participated in the data collection phases of the study. All subjects had also participated in IST-1 and had significant experience with both the MKIII and the POGO. At this time, no available female astronauts properly fit in the MKIII suit.
For suited testing, the MKIII suit was used as it represents a suit concept that provides the dynamic ranges of motion considered necessary for a wide variety of planetary EVA tasks within today’s technology level given other constraints that must be considered in pressure garment design. The MKIII also had an existing method to integrate with the POGO and allowed for varied pressure testing. Thus, the MKIII provides a valid test bed from which attainable requirements for future suit development can be derived.
Each subject performed a battery of tasks representing typical activities expected during lunar EVA performance. Tasks included, in the order of performance, are small rock pickup, large rock pick up, shoveling (biomechanics emphasis), shoveling (metabolic emphasis), kneel and recover, rock transfer, hammering, ladder placement, and busy board. This testing protocol was performed during all suited and shirtsleeve configurations except for the two suited conditions at 34.5 kPa (5.0 psi) and 44.8 kPa (6.5 psi). These higher-pressure conditions were not tested because subjects used the Phase VI gloves with the MKIII suit, which were believed to provide better manual dexterity but were only rated to 29.6 kPa (4.3 psi).
Each subject walked on a level treadmill for three minutes at his lowest walking speed while carrying a weighted load in front of him. Each subject completed three different loads of 4.5, 9.1, and 13.6 kg (10, 20, and 30 lb) for three minutes each. The 4.5- and 13.6-kg loads were round rubber medicine balls, and the 9.1-kg load was a rectangular sandbag. This testing protocol was performed at the POGO suited configuration of 29.6 kPa (4.3 psi), 121-kg suit mass, and lunar gravity. It was also completed during the shirtsleeve configuration at lunar gravity.
For inclined walking, shirtsleeve baseline costs and the cost of additional weight account for most of the energy cost; the percentage contribution from both of these factors increased as grade increased. For exploration tasks, the shirtsleeve baseline costs were also present, but weight actually had the opposite effect and acted to decrease metabolic rate.
Variation in suit pressure at simulated lunar gravity did not significantly affect metabolic rate with either exploration tasks or inclined walking. Task type and the walking grade primarily determined metabolic cost. Although there was little to no variation from changing suit pressure, it is important to note that exploration tasks did not test at the higher pressures of 34.5 or 44.8 kPa. In addition, while the tasks often involved gripping and hand use, no task was extremely hand-intensive for long periods of time.
Norcross JR, Clowers KG, Clark T, Harvill L, Morency RM, Stroud LC, Desantis L, Vos JR and Gernhardt ML. Metabolic costs and biomechanics of inclined ambulation and exploration tasks in a planetary suit. Houston TX: National Aeronautics and Space Administration, Lyndon B. Johnson Space Center; 2010. NASA Technical Publication NASA/TP-2010-216125.
Norcross JR. Using analogs for performance testing of humans in spacesuits in simulated reduced gravity. Houston TX: National Aeronautics and Space Administration, Johnson Space Center. September 24, 2013. NASA Technical Publication NASA/TP-2013-20140002724. [NTRS]
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