- 1 - Chapter 22 LIFE SUPPORT AND PERFORMANCE ISSUES FOR EXTRAVEHICULAR ACTIVITY (EVA) Dava Newman, Ph.D. and Michael Barratt, M.D. 22.1 Introduction Defining the goals for future human space endeavors is a challenge now facing all spacefaring nations. Given the high costs and associated risks of sending humans into Earth orbit or beyond – to lunar or Martian environments, the nature and extent of human participation in space exploration and habitation are key considerations. Adequate protection for humans in orbital space or planetary surface environments must be provided. The Space Shuttle, Mir Space Station, Salyut-Soyuz, and Apollo programs have proven that humans can perform successful extravehicular activity (EVA) in microgravity and on the Lunar surface. Since the beginning of human exploration above and below the surface of the Earth, the main challenge has been to provide the basic necessities for human life support that are normally provided by nature. A person subjected to the near vacuum of space would survive only a few minutes unprotected by a spacesuit. Body fluids would vaporize without a means to supply pressure, and expanded gas would quickly form in the lungs and other tissues, preventing circulation and respiratory movements. EVA is a key and enabling operational resource for long- duration missions which will establish human presence beyond the Earth into the solar system. In this chapter, EVA is used to describe space activities in which a crew member leaves the spacecraft or base and is provided life support by the spacesuit. To meet the challenge of EVA, many factors including atmosphere composition and pressure, thermal control, radiation protection, human performance, and other areas must be addressed. Compared to Earth-based capabilities, performance during in-space EVA is enhanced for some functions and degraded for others. EVA offers many advantages for accomplishing space missions. The astronaut is present at the worksite and has the following capabilities: flexibility, dexterous manipulation, human visual interpretation, human cognitive ability, and real time approaches to problems. The factors which may degrade performance include pressure suit encumbrance, prebreathe requirements, insufficient working volume, limited duration, sensory deprivation, and poor task or tool design [34]. EVA, as well as robotics and automation, expand the scope of space operations. A thorough understanding of EVA capabilities will help bring about the integration of humans and machines for future missions. In addition to microgravity EVAs, the partial gravity environments of the Moon and Mars require advanced EVA hardware and performance capabilities. 22.2 Historical Background - 2 - In March of 1965, cosmonaut Alexei Leonov became the first human to walk in space (Figure 22.1). Attached to a 5-meter long umbilical which supplied him with air and communications, Leonov floated free of the Voskhod spacecraft for over ten minutes. In June of the same year, Edward White became the first American astronaut to egress his spacecraft while in orbit. White performed his spectacular space walk during the third orbit of the Gemini – Titan 4 flight. Table 22.1 summarizes Russian and U. S. extravehicular activity to date. Insert Figure 22.1 here Although some of the early EVA efforts of both programs were plagued with problems, the feasibility of placing humans in free space was demonstrated. The Gemini EVAs showed the necessity of providing adequate body restraints to conduct EVA and demonstrated the value of neutral buoyancy simulation for extended duration training in weightlessness. The second Russian EVA saw the partial transfer of a crew from one craft to another. An important anomaly was evident in photographs of the Soyuz 5 spacesuit design. Rather than wearing a large backpack-type primary life support system, the crew wore air supplies strapped to their legs. Locating the life support on the front part of the legs made it possible to solve the problem of crew transfer through the Soyuz "manholes with relatively small dimensions (66-cm diameter)" [49]. During the Apollo program, EVA became a useful mode of functioning in space, rather than just an experimental activity. Twelve crew members spent a total of 160 hours in spacesuits on the moon, covering 100 kilometers (60 miles) on foot and with the lunar rover, while collecting 2196 soil and rock samples. The Apollo EVAs were of unprecedented historical importance as Neil Armstrong and Edwin "Buzz" Aldrin became the first humans to set foot on another celestial body. Many successful scientific experiments were carried out during the Apollo EVAs. The EVA spacesuits were pressurized to 26.2 kPa (3.9 psi) with 100% oxygen, and the Apollo cabin pressure was 34.4 kPa (5 p s i ) with 100% oxygen. During pre-launch, the Apollo cabin was maintained at 101.3 kPa (14.7 psi) with a normal air (21% oxygen and 79% nitrogen) composition. Just before liftoff, the cabin was depressurized to 34.4 kPa (5 p s i ). To counteract the risk of decompression sickness after this depressurization, the astronauts prebreathed 100% oxygen for three hours prior to launch (This will be discussed in greater detail subsequently). Despite these efforts, Michael Collins reported a suspicious pain upon Apollo 11 orbital insertion that fortunately resolved spontaneously; this episode possibly represented joint pain associated with decompression sickness [9]. The potential benefits of EVA were nowhere more evident than in the Skylab missions. When the crew first entered Skylab, the internal temperature was up to 71°C (160°F), rendering the spacecraft nearly uninhabitable. The extreme temperatures resulted from the loss of a portion of the vehicle's outer skin as well as a lost solar panel. After failure of a second solar panel deployment and the consequent loss of power and cooling capability, astronauts Joseph Kerwin and Charles "Pete" Conrad salvaged the entire project by rigging a solar shade through the science airlock and freeing the remaining solar panel during EVA. The paramount flexibility offered by EVA for accomplishing successful space missions, operations, and scientific endeavors was realized during Skylab. - 3 - After a nine year lapse in Russian extravehicular activity, cosmonaut Georgi Grechko performed a critical EVA to examine the cone of the Salyut 6 docking unit which was thought to be damaged. Additional EVAs were performed during Salyut 6 in order to replace equipment and to return experimental equipment to Earth which had been subjected to solar radiation for ten months. The success of the Salyut 6 program during 1977–1981 brought about the Salyut 7 space station program. Successful EVAs were performed to continue studying cosmic radiation and the methods and equipment for assembly of space structures. Ten EVAs were performed during the Salyut 7 – Soyuz missions; experience and expertise in space construction, telemetry, and materials science was gained. On 25 July 1984 during her second spaceflight (Her first flight was in August 1982.), cosmonaut Svetlana Savitskaya became the first woman to perform an EVA (Figure 22.2), during which she used a portable electron beam device to cut, weld, and solder metal plates. Insert Figure 22.2 here From 1983 through 1985, 13 two-person EVAs were performed during STS (Space Transportation System, commonly called Space Shuttle) missions. During these missions, trained crew members have responded in real time to both planned mission objectives and unplanned contingencies. Evaluation and demonstration of the Extravehicular Mobility Unit (EMU), a 29.6 kPa (4.3 psi) spacesuit; the Manned Maneuvering Unit (MMU); the Remote Manipulator System (RMS, commonly known as the Canadian Arm); and specialized tools have resulted in the repair of modules, the capture and berthing of satellites, and the assembly of space structures. The STS EMU is self-contained; therefore, an umbilical for its life support and communications systems is unnecessary. Advanced spacesuit concepts incorporate self- contained life support systems (both the American and Russian spacesuits) and modular components (the American spacesuit). Modularity allows for ease of resizing to fit humans ranging in size from fifth percentile females to ninety-fifth percentile males, a distinct advantage over the custom-fitted suits previously used. Several firsts were accomplished during Space Shuttle EVAs, including the first American woman EVA performed by Kathryn Sullivan during mission 41–G. (In this nomenclature, 4 stands for the year 1984, 1 is for the launch site: Kennedy Space Center, and the G is the order of the launch. This numbering system has been subsequently changed back to the more straight forward STS-XX sequential numbering system.) The EVA by Bruce McCandless in February 1984 was the first space trial of the MMU (Figure 22.3). The MMU is a completely separate space propulsion module which combines with the EMU to allow astronauts to maneuver up to 366 meters (1200 ft) away from the spacecraft. However, it is no longer manifested on Space Shuttle EVA missions due to the accuracy and success the astronaut pilots have had in bringing the EVA crew members to their desired orbital location by precise maneuvering of the orbiter. The first American spacewalk in over five years took place on 14 April 1991. Astronauts Jerry Ross and Jay Apt performed an unscheduled EVA on STS-37 in order to shake loose the antenna of the Gamma Ray Observatory prior to deployment. The crew members' second EVA consisted of conducting the Crew and Equipment Translation Aid (CETA) flight experiment which investigated four modes of locomotion (a manual cart, a mechanical cart, an electrical cart, - 4 - and a tether shuttle) for moving along the outside of the proposed space station truss. The manual cart was selected as the optimum translation aid. A second EVA Translation Experiment (ETE) on STS-37 provided the recommendation that non-rigid translation technologies should be considered for accessing areas of Space Station Freedom which do not require frequent service.