National Geographic : 1957 Apr
577 There was no need to recover the rocket's instruments from the bottom of Hudson Bay; they had "talked" their findings down to earth by telemetering instruments. The story would be told by wavy lines on film. I next saw Mr. Spencer weeks later. "How much colder was it in the ionosphere than on the ground at Fort Churchill?" I asked. "We don't know yet," he answered. "It'll be months before we have our data analyzed, but they probably will show temperatures to be around 0°F. at 65 miles." Balloon flights have shown that temperatures drop as low as minus 90° F. at altitudes of seven to ten miles. Rocket flights have revealed that higher up the air becomes warmer, approaching ground level temper atures at 30 miles. Why? Because at that altitude ozone absorbs the sun's ultraviolet energy and con verts it into heat. Air Ocean Is Both Cold and Hot Another drop in temperature occurs above 30 miles, again reaching a low of about minus 90° F. at 50 miles. From 50 miles on out the temperature rises once more. How far into space this rise continues, scientists do not know for sure, nor can they explain it to everyone's satisfaction. They believe temperatures may reach 2500°F. or more at the outer limits of the ionosphere. Speeding at 3,500 miles an hour, the rocket developed such tremendous air friction that its surface tempera ture rose hundreds of degrees. Yet instruments in its nose cone determined outside air temperatures, inde pendent of the missile's heat.