John's adventuring took place on the ground as well as in outer space. In 2002, he and NASA consultant Howard Donner tackled North America's highest peak, Mount McKinley, as part of a study on how altitude affects body temperature. The research required the men to swallow tiny, pill-sized thermometers, which measured their temperature during the trek. The pair, whose efforts were featured in a PBS NOVA episode titled "Deadly Ascent," reached 17,200 feet before having to turn back due to eight days of stormy weather. Disappointed but undaunted, two years later, John became the only American astronaut to reach the summit of Mount McKinley, leading a team of other NASA explorers.