Thermoregulatory models of space shuttle and space station activities.

Background: Thermoregulation is critical for survival in space, especially during contingencies demanding of human cognitive and physical performance. A review of the negative feedback human thermoregulatory system is provided. The Advanced Crew Escape Suit is worn by astronauts during ascent and descent on the Space Shuttle to provide active cooling for nominal and contingency operations and protection from loss of cabin pressure mishaps. Failure of a thermal system control element during a recent Shuttle flight resulted in a single point failure that could have elevated cabin temperature, possibly resulting in cognitive deficits of the pilot during the reentry and landing phases.

Methods: The efficacy of the existing cooling equipment and procedures for maintaining crew thermal comfort in the event of such a failure was assessed. The Wissler and 41-node thermoregulatory models were used to conduct a parametric study of Shuttle cabin temperatures and resulting thermal effects on crew.

Results: Under high metabolic loads, crewmember core temperatures and heat storage are shown to increase beyond allowable limits using this analysis. Resulting levels of thermal stress may exceed standardized limits, after which cognitive performance and manual tracking ability are diminished.

Discussion: The operational procedure for entry and landing during this failure scenario may result in significant thermal compromise to crewmembers, including cognitive and manual performance deficits. Revision of the flight rule governing crew actions during compromise of cabin thermal control has been undertaken to minimize thermal stress on returning Shuttle crewmembers. Modifications to the crew thermal protection system for the Shuttle are suggested.