Advanced Extravehicular Activity Biomedical and Energetics Performance and Spacesuit Assessment
Principal Investigator:
Dava Newman, Ph.D.
Organization:
Massachusetts Institute of Technology
Extravehicular activities (EVAs) are dangerous endeavors that require extensive planning. Dr. Dava Newman’s project is designed to enhance EVA, or spacewalk, research and planning. Newman and her colleagues provided robotic testing of a spacesuit exoskeleton knee joint and developed an EVA mission planning tool.
Testing of the knee joint gave a better understanding about the movements of an astronaut and spacesuit during a spacewalk. The 3-D EVA mission planning tool will assist astronauts in planning and navigating their paths across planetary or lunar surfaces while providing information about timelines and life-support status. Finally, the researchers reviewed data and quantified spacesuit movements and energy needed to conduct a spacewalk on another planet.
The project’s Earth applications include the improvement of garments to allow for better movement while fulfilling protection requirements, such as the garments worn by firefighters. Also, the planning tool will have benefits for excursions in the desert, underwater and other extreme environments.
NASA Taskbook Entry
To support NASA and NSBRI advanced extravehicular activity (EVA) biomedical research, the Massachusetts Institute of Technology (MIT) EVA research team provided robotic spacesuit testing of a spacesuit exoskeleton knee joint, developed a planetary EVA mission planning capability, and reviewed biomechanic and energetic results of partial gravity locomotion.
Human and robotic testing of a Space Suit Simulator (S3) was performed by Professor Newman, her team and MIT for NASA colleagues (Dr. Schaffner of Wyle Laboratories and Dr. Gernhardt of NASA Johnson Space Center). The S3 program involved testing a right knee joint brace, or joint suit simulator, on the Robotic Space Suit Tester (RSST) at MIT in the Man-Vehicle Laboratory. Testing requirements achieved:
- Characterization of the sensitivity of the joint torque versus angle relationship on joint displacement speed;
- Hysteresis behavior of the joint; quantification of the adjustability of joint range of motion; and
- The adjustability of joint friction and stiffness.
All knee results show hysteresis of the joint, which is a characteristic of both the robot and actual spacesuit joint torques. Adjusting trajectory speed has little effect on maximum joint torques. For range of motion, three configurations of the knee joint were tested: one without any limitation (0 - 130) and two smaller ranges (20 - 110 and 40 - 90). Torques were higher only for the most highly constrained case. As expected, joint torque increases with friction, but we also found that the range of motion decreases with increasing friction. Preliminary testing of aerogel swatches for EVA thermal protection was also performed. The swatches were sewn into arm sections and tested over the RSST elbow. These garments were considerably stronger than expected and allowed for 130 degrees of movement without failing.
Another research deliverable under this project included developing a three-dimensional (3D) EVA mission planning tool. Applied to future planetary manned missions, an EVA mission planner will assist astronauts plan and navigate their traverses and will also inform the crew member of planetary terrain mapping (digital elevation maps, editing, waypoint automation and path planning, 3D viewing and zooming), sun illumination levels, life support status, metabolic costs, scientific timelines and emergency walkback calculations. This research effort investigated the appropriate balance between humans and automation for geospatial path problem solving within the high-risk domain of human planetary surface exploration, where decisions are time critical and humans must adapt to uncertainty.
As a human-machine interface, the planner should function efficiently and intuitively with the astronaut. Cognitive decision making tools were studied, which showed that the path planning process should include three steps:
- Collecting external information;
- Integrating the information together with reference to costs and goals; and
- Generating the path iteratively using a sensitivity analysis.
The EVA mission planner allows for the collection of all pertinent information, such as physiological factors, navigating waypoints, obstacle settings/angles, etc., and then uses a geographical information system for terrain data. An optimization algorithm then determines the most efficient path to achieve the desired waypoints using an EVA metabolic rate model. The best path is shown on a map in 3D for clear guidance to the astronaut. Early trials of the planner have proven to be a success. Navigating systems will be highly valuable to astronauts during EVAs on planetary surfaces.
The final component of this research effort was to review and quantify spacesuit biomechanics and energetics for planetary locomotion EVAs. We developed a framework for comparison of energetics data across and between all lunar EVA studies published in the literature. Major factors affecting the energetic cost of movement while wearing a spacesuit include suit pressurization, gravity, velocity, surface slope and spacesuit configuration. Apollo lunar surface EVA on-foot locomotion metabolic rates, while unexpectedly low, were higher than other activity categories. In a follow-on publication, we hypothesized that spacesuit legs act as springs during running, thereby lowering cost of transport relative to spacesuited walking. We transformed data from suited and unsuited energetics studies into a common format and developed a regression equation for specific resistance, S, (energy per weight per distance) based on the Froude number (a non-dimensional parameter associated with gait transitions), surface slope, gravity, and spacesuit pressure. A regression on S achieved an adjusted R2 of 0.83; all factors were significant (P<0.0005). No additional evaluated factors met the acceptance criteria. The categorical regression, but not the hypothesis test, suggested that the running group had reduced efficiency per unit time; both tests suggested that the running group had increased efficiency per unit distance. Findings suggest that gas-pressure spacesuit legs function as springs during running, including the finding of higher efficiency per unit distance during running, despite the presumed increased work against spacesuit joint torques at higher velocities.
Robotic Space Suit Tester (RSST) testing allowed for characterization of knee joint and aerogel garment torques. Our study refines a protocol to allow for the quantitative improvement of garments worn on Earth. Materials, designs and tailoring techniques can be tested in short time frames to allow for quick optimization of thick or stiff garments. For instance, firefighter pants must protect the wearer from extremes of temperature and also injury from falling debris, and yet allow quick locomotion and ladder climbing. The RSST protocol provides a framework and hardware for measuring joint torques - and thereby resistance to free movement - over extended periods with repetitive and precise movements that would not be possible for human subjects. Other tight or restrictive garments, such as therapeutic and rehabilitation designs, could also be tested using the system and protocol so that appropriate skin compression is produced while minimizing movement constraints.
The extravehicular activity mission planner will aid in the safe and efficient planning of any Earth traverse, particularly where the subject/group needs to manage navigation, physiologic- and mission-specific information, all in time-finite situations. Planning traversals for complex scientific or information-rich exploration can be dangerous and inefficient. Further, managing significant information becomes increasingly difficult when the task changes to real-time re-planning of a traversal (i.e. new discoveries or discrepancies) between planned and observed conditions demanding immediate selection of a new path while not violating mission constraints. Applications for this mission planner include basic hiking and exploring, various scientific missions - such as geologic surveys in desert conditions and especially expeditions to any extreme environments, such as polar expeditions and deep-sea diving.
