Extravehicular activity (EVA), also known as a space walk, is any activity performed by astronauts outside their spacecraft. EVA may be performed on orbit, such as outside the Space Shuttle or the International Space Station, or on a planetary surface such as Mars or on the Moon. Astronauts wear a pressurized suit that provides environmental protection, mobility, life support, and communications while they work in the harsh conditions of space.
About the EVA Physiology, Systems, & Performance (EPSP) Project
 The EVA Physiology, Systems and Performance (EPSP) Project seeks to understand human performance during EVA with the aim of developing more safe and efficient systems for Exploration missions and the Constellation Program. This Project will conduct a number of studies to understand medical safety and human performance issues related to working in partial-gravity environments.
Goals and Objectives:
- Develop Exploration Mission EVA suit requirements which optimize human performance
- Develop validated EVA prebreathe protocols that meet medical, vehicle, and habitat constraints while minimizing crew time and thus increasing EVA work efficiency
- Define acceptable Decompression Sickness (DCS) risks for exploration missions
Use of Multiple Test Environments
Multiple testing environments are necessary because no single Earth environment can perfectly simulate weightlessness or partial gravity. The project will characterize human  Image right: An astronaut performs a 10 km "Walk back" to test his ability to return to a habitat in the event of a rover vehicle failure on the Moon. EVA performance and suit interactions in studies using several test beds, including the underwater NEEMO and Neutral Buoyancy Laboratory facilities, a lunar-simulated crater, and NASA's partial gravity simulators. using these varied testing environments; NASA can gain a more complete understanding of human performance issues related to EVA and thus enable optimized EVA systems and suits in the future.
Advanced Walkback Test (AWT) and Future Suit Evaluations
Performed in conjunction with JSC's Crew & Thermal Systems Division (CTSD) in Summer 2006, a test was performed using suited and unsuited (regular clothes) subjects in a partial-gravity simulation system to assess the ability of an unaided suited crewmember to walk 10 km in the event of a rover breakdown. Baseline data was collected to understand the physiological, biomechanical, and subjective aspects of exercise in partial gravity, and to enable development of future EPSP studies.
Future series of tests will expand on knowledge gained in the AWT and assist in identifying and understanding the EVA suit factors that affect human performance such as center of gravity (cg), inertial mass, ground reaction forces (GRF), suit weight, and suit pressure. These characterizations then will be used to optimize human performance while wearing the EVA suit and lead to the development of Exploration Mission EVA suit design requirements.
NASA Extreme Environment Mission Operations (NEEMO)
 In pursuit of understanding biomedical performance requirements, particularly EVA biomechanics and center of gravity control, NEEMO activities are conducted at the underwater ocean laboratory named Aquarius. Aquarius is located in the Florida Keys National Marine Sanctuary and deployed 3.5 miles offshore, at a depth of 60 feet. Image right: A NEEMO crewmember wearing a mock-up of the EVA portable life support system (PLSS) walks up and down a ladder outside the underwater Aquarius habitat. The PLSS mock-up was placed in different configurations to test astronauts' ability to perform EVA tasks when their center of gravity is moved up, down, forward, and/or backward. Aquanauts live in Aquarius for 7 to 14 day missions using saturation diving to conduct simulated NASA mission objectives. The partial gravity environment and ocean floor terrain offer the most realistic simulation of a multi-day Lunar Mission available at this time. The EPSP team currently conducts activities related to task efficiency, work efficiency, optimal suit weight assessment, and center of gravity assessments.
Future Studies will investigate
- Exploration decompression sickness risk definition and contingency plan development
- EVA biomechanical performance requirements and assessments
- EVA suit trauma countermeasures
- EVA nutrition and delivery systems
- Biomedical Sensors and control algorithms
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