1996-07-01

Assessment of the Atmospheric Parameters of the Space Craft and Space Suit Ensuring Decompression Safety During Episodic Extra-Vehicular Activity 961419

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 experiments allowed the display in a diagram of the ratio of permissible magnitudes of final pressure (the operational pressure mode in the space suit) for a duration of preliminary exposure in normoxic hypobaric conditions.
The revealed dependence and equations describing it were the basis of nomogram construction determining a common interrelation between the primary atmosphere parameters in a space craft (total pressure and oxygen content), the values of oxygen and nitrogen partial pressure in alveolar air, the maximum allowable supersaturation ratio and value of operational pressure in space suit. This nomogram can estimate different variants of the appropriate combination of the initial space cabin atmosphere parameters and minimum value of the space suit pressure for egress to outer space without oxygen prebreathing.

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