As a physical environment, space begins at about 125 miles above the earth, but as a physiological environment, it begins at about 63,000 feet. At this altitude the atmospheric pressure becomes so low that fluids boil off at body temperature. The main function of the pressure suit was to save your life at the extreme altitudes, temperatures and speeds the SR-71 flew. Above 45,000 feet a crew member's Effective Performance Time (EPT) is between nine to twelve seconds without oxygen. Frost bite to the skin would occur rapidly at the SR-71's operational altitude, where the outside air is -56 degrees C. Without a suit on at 80,000 feet, and the loss of all cabin pressure or an ejection scenario, you would not survive. |
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