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The analysis of 30 years of Russian EVA experience and research on earth enables us to make a number of fundamental conclusions (1, 2, 3, 4, 5, 6 and 7). The suit life support subsystem (LSS) parameters including gas composition, gas pressure, thermal control system, provide for environments close to those of physiological norm. The Russian EVA suit allows a crewmember to retain necessary scope of motions, tactile sensibility, and the ability to see and communicate which are necessary for performing scientific and repair activities outside the spacecraft. The duration of space missions (up to a year) and repetition of EVAs every 2-3 days do not affect crewmember capability to perform the EVA tasks with the metabolic rate of 320 kcal/h during the 6-7 hour EVA sortie. Medical monitoring and analysis of the LSS parameters allow us to reliably control crewmember state of health, forecast and prevent its unfavourable changes.

The operating pressure value is one of the principal considerations for trade-off analysis of the space suit enclosure and the individual life support subsystem (LSS). From the physiological point of view, the same level of pressure in the suit and space vehicle reflects the best solution. Current Russian space vehicles and orbiting stations use the “Earth atmosphere”. A suit operating pressure at such a level would result in complicated and technically unreasonable designs. Improved mobility of the pressurized suit and enhanced performance characteristics of the LSS can be offered with the minimized positive pressure. However, the minimized suit pressure concept leads to the increased risk of crewmember decompression sickness. Therefore, the suit operating pressure selection calls for a trade-off of physiological tolerances of the crewmember versus technical feasibility of this or that solution as principal considerations.