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The risk of decompression sickness (DCS) inherent in extra-vehicular activity (EVA) is reduced through the usage of hypobaric normoxic atmosphere. The safety of decompression protocols was evaluated during EVA simulation in the PCC-270 pressure chamber complex according to DCS frequency and tissue supersaturation ratio. The test program included 15 man rated test runs (1828 man- runs) with 123 test subjects aged 19-54. The aim of the test program was to select decompression safe protocols for transfer from hypobaric environment to a reduced pressure mode in the Russian space suit. These experiments allowed to display in nomogramm form the ratio of operative pressure mode in the extravehicular space suit to the duration of a preliminary exposure in normoxic hypobaric conditions.

The practical purpose of the study on human thermal regulation during space operation is to scientifically justify an automatic thermal control system (ATCS). The primary goal of the ATCS is to maintain the thermal comfort during all possible types of human activities in the most fiendly way. The main purpose of ATCS development is the identification of physiologically valuable requirements and validation of optimal laws used to control human thermal status in the suited mode. Such an identification is possible if we have a good knowledge of the control aim and current thermal status. That means that one needs to a criterion for or an assessment of interrelationship between thermal status, activities and disturbances. The model of human thermal regulation and metabolism in a space suit with a ventilation loop and a water cooling loop is a theoretical basis for ATCS experimental tests.

The report presents the values of supersaturation ratio expected during space flights in chart form, covering the range 400-950 mm Hg of total atmospheric pressure and 150-400 mm Hg final space suit pressure. These charts allow users to rapidly find decompression risk received in the most critical decompression protocols for extravehicular activity either in nominal situations or during emergency activity. Decompression safety transfer to the reduced pressure has been established as a result of long-standing man rated tests during two decades. Tests aimed at selecting decompression-safe protocols for transition from a hypobaric normoxic environment to reduced pressure. Experimental data is discussed and some protocols for safe transition to reduced pressure are recommended.

The human thermoregulation study during space operation has such practical result as scientific justification of automatic thermal control system (ATCS). A primary goal is a maintenance of the thermal comfort during all possible types of human activity. It is an optimal control aim to ATCS. The main purpose of ATCS development is an identification of physiologically valuable requirements and validation of optimal laws to control human thermal status in the space suit conditions. An identification is possible only if we have a good knowledge of the control aim and current thermal status. It needs to have a criterion or assessment of interface between thermal status, actions and disturbances. The model of human thermoregulation and metabolism in space suit with ventilation loop and water cooling loop is a theoretical basis for experimental tests of ATCS. Our model has two interdependent parts: 1) anatomical/physiological compartment and 2) technical compartment.

Extravehicular activity (EVA) is an essential part of space missions. When International Space Station ALPHA (ISSA) is fully operational, EVA assembly, installation, maintenance and repair operations will become everyday repetitive work activity in space. Due to the high cost of EVA sorties, a logical step is to try to improve the productivity of the EVA astronaut in order to increase the amount of labor per EVA hour and to optimize the work/rest regime. This is a main goal of decompression protocol development. In order to allow the astronauts sufficient productivity within the EVA space suit it is necessary to operate the suit with an internal pressure lower than 1 atmosphere. The suit pressure of approximately 0.3-0.4 atmosphere (30-40 kPa or 220-300 mm Hg ) induces the risk of decompression sickness (DCS) by the formation of gas bubbles (GB) from excess nitrogen dissolved in the organism by breathing air at normal pressure in the space cabin atmosphere.