LIFE SUPPORT SYSTEMS: EXTRAVEHICULAR ACTIVITY (EVA)

The gear worn during spacewalks includes small, light-weight, and totally self contained life support systems. The complete system is know as the Extravehicular Mobility Unit (EMU) and consists of the Space Suit Assembly (SSA) and the Portable Life Support Subsystem (PLSS). The PLSS is worn as an integrated "backpack".

The "spacesuit", used during the Mercury Program, was a modification of the Navy's MK-IV high altitude pressure suit. The suit provided cooling and acted as a back-up system in case the cabin lost pressure. The first American EVA occured during the following Gemini Program. Six EVAs were performed (2 hour maximum) during the ten manned Gemini flights. Life support was provided to the suit from the cabin via a 24 foot umbilical. For the Apollo moon missions an EMU with an integral life support backpack was used which was capable of supporting six hour EVAs. For Skylab, a modified Apollo suit was used with life support provided from the cabin via a 60 foot umbilical. The EMU developed for Space Shuttle, with a tightly integrated PLSS backpack, was designed to be reusable (like the spacecraft). Future systems for ISSA will support eight hour EVAs.

The basic life support functions provided by the EMU include: pressure maintenance, oxygen delivery, ventillation, and control of temperature, humidity, carbon dioxide and trace organic contaminants (odors). The pressure inside the suit (4.3 psia) is intentionally kept low to enhance the astronaut's mobility. Because the cabin pressure is a 14.7 psia normal atmospheric mixture of nitrogen and oxygen, steps must be taken to minimize the potential for decompression sickness ('the bends') as a result of the EVA. Prior to EVA cabin pressure is reduced to 10.2 psia for 24 hours. The astronauts then pre-breathe pure oxygen for 40 minutes. Inside the suit, ventillation is provided by oxygen flow over and in front of the face. This also prevents fogging of the helmet. Carbon dioxide and trace organics are removed using LiOH and activated carbon sorbents. Cooling is provided by water circulating through the undergarment. Heat rejection occurs as water freezes on porous plates and then sublimes to the vacuum of space.

REFERENCES

Adlehart, O.J., Rosso, M.J., Jr., and Marmolejo, J., A Fuel Cell Energy Storage System Concept for the Space Station Freedom Extravehicular Mobility Unit, SAE Technical Paper Series No. 891582, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Ames, B.E., and Iovine, J.V., LSOPP II - A Program for Advanced EVA System Modeling and Trade Studies, SAE Technical Paper Series No. 901264, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Balinskas, R., McBarron, J.W., and Spampinato, P.M., Shuttle Extravehicular Mobility Unit (EMU) Operational Enhancements, SAE Technical Paper Series No. 901317, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Beckstrom, P., Rosso, M.J., Jr., and Adlhart, O.J., Development of a Fuel Cell for the EMU, SAE Technical Paper Series No. 901318, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Brown, M.F., and Schentrup, S.M., Requirements for Extravehicular Activities on the Lunar and Martian Surfaces, SAE Technical Paper Series No. 901427, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Buchman, O.A., MacKnight, A.K., Gomez, D., and Supra, L.N., Development of a Regenerable Metal Oxide CO2 Absorber for EMU Applications, SAE Technical Paper Series No. 961483, presented at 26th International Conference on Environmental Systems, Monterey, CA, July 8-11, 1996.

Buck, C.A., Space Station Freedom Airlock/Extravehicular Activity Operations, SAE Technical Paper Series No. 901396, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Coleman, W., and Reynolds, D., Advanced Portable Life Support System Component Integration and System Testing, SAE Technical Paper Series No. 891580, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Filburn, T., Nalette, T., Genovese, J., and Thomas, G.A., Advanced Regenerable CO2 Removal Technologies Applicable to Future EMU's, SAE Technical Paper Series No. 961484, presented at 26th International Conference on Environmental Systems, Monterey, CA, July 8-11, 1996.

Filipenkov, S.N., Voroblev, G.F., and Isseev, L.R., Influence of Two-Hour Oxygen Prebreathe on the Decompression Sickness Incidence at Pressures of 145, 198, and 220 mm Hg, SAE Technical Paper Series No. 961420, presented at 26th International Conference on Environmental Systems, Monterey, CA, July 8-11, 1996.

Furr, P.A., Monson, C.B., Sears, W.J., and Abeles, F.J., Physiological Aspects of EVA, SAE Technical Paper Series No. 860991, presented 16th Intersociety Conference on Environmental Systems, San Diego, CA, July 14-16, 1986.

Hart, J.M., Borghese, J.B., Chang, C.H., and Cusick, R.J., Portable Life Support System Regenerative Carbon Dioxide and Water Vapor Removal by Metal Oxide Absorbents Preprototype Hardware Development and Testing, SAE Technical Paper Series No. 921299, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Hart, J.M., Chang, C.H., Cusick, R.J., and Stonesifer, G.T., Comparison of Metal Oxide Absorbents for Regenerative Carbon Dioxide and Water Vapor Removal for Advanced Portable Life Support Systems, SAE Technical Paper Series No. 911343, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Himel, V., Abeles, F.J., Auman, J., and Tqi, T.O., Automatic Sequencing and Control of Space Station Airlock Operations, SAE Technical Paper Series No. 891590, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Jacobs, G., A Methodology for Choosing Candidate Materials for the Fabrication of Planetary Space Suit Structures, SAE Technical Paper Series No. 901429, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Kosmo, J.J., Design Considerations for Future Planetary Space Suits, SAE Technical Paper Series No. 901428, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Lomax, C., and Webbon, B.W., A Direct-Interface Fusible Heat Sink for Astronaut Cooling, SAE Technical Paper Series No. 901433, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Lutz, G.C., Melgares, M.A., Peacock, P.R., and Wilde, R.C., EMU Processing - A Myth Dispelled, SAE Technical Paper Series No. 911348, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Murray, R.P., An Air Bearing Fan for EVA Suit Ventilation, SAE Technical Paper Series No. 901432, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Murray, R.P., A Gas-Bearing Compressor System for Space Station Airlock Gas Recovery, SAE Technical Paper Series No. 891606, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Newbold, D.D., Ray, R.J., Pledger, W.A., McCray, S.B., and Brown, M.F., Investigation of Humidity Control Via Membrane Separation for Advanced Extravehicular Mobility Unit (EMU) Application, SAE Technical Paper Series No. 891507, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Ollivier, Y., and Diener, M., Development of the Suit Enclosure of the European EVA Spacesuit, SAE Technical Paper Series No. 901244, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Planert, C., Kremer, P., and Witt, J., Development of Sublimator Technology for the European EVA Space Suit, SAE Technical Paper Series No. 911577, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Prouty, B.R., Wilde, R.C., and Gan, M., Evolution of the Extravehicular Mobility Unit for Future Missions, SAE Technical Paper Series No. 911349, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Skoog, A.I., and Ollivier, Y., European Space Suit Design Concept Verification, SAE Technical Paper Series No. 911575, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Smith, L.F., French, J.D., Nair, S.S., Miles, J.B., and Webbon, B.W., Evaluation of Human Thermal Models for EVA Applications, SAE Technical Paper Series No. 961487, presented at 26th International Conference on Environmental Systems, Monterey, CA, July 8-11, 1996.

Strumpf, H.J., Thermal Sink for the Advanced Extravehicular Mobility Unit Portable Life Support System, SAE Technical Paper Series No. 891581, presented 19th Intersociety Conference on Environmental Systems, San Diego, CA, July 24-26, 1989.

Switzer, K.L., Space Station Freedom Airlock Outfitting to Support Extravehicular Activity (EVA), SAE Technical Paper Series No. 901321, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Thomas, G.A., and Rouen, M.N., Preliminary Design Methodology for an Advanced Extravehicular Mobility Unit Portable Life Support Subsystem, SAE Technical Paper Series No. 951672, presented at 25th International Conference on Environmental Systems, San Diego, CA, July 10-13, 1995.

Vath, R., and Skoog, A.I., EVA Life Support Design Advancements, SAE Technical Paper Series No. 901245, presenated 20th Intersociety Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Wilson, J.L., and Lawson, B.M., Investigation into Venting and Non-venting Technologies for the Space Station Freedom Extravehicular Activity Life Support System, SAE Technical Paper Series No. 901446, presenated 20th Intersociety Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990.

Return to Regenerative Life Support

Copyright © 1996, James E. Atwater