Would you rather blast off into the cold emptiness of space in a fallible rocket, or drag yourself past 200 dead bodies to the inhospitable summit of Mount Everest? Former astronaut Scott Parazynski is the only person on Earth who has conquered both these extreme feats, and it turns out that the challenge closer to home is the one that made his heart race the most. Once you survive the rocket launch, space is rather tranquil, with beautiful views, and you’re well looked after by the smartest support team of scientists in the country, Parazynski points out. On your way up the tallest mountain on Earth, however, the threat of death looms with every step. You cannot eat enough or breathe enough to nourish your body, and once you reach your goal — guess what? You’re only halfway. Listen to Parazynski describe these two incredible experiences, and the psychological impact of finding somewhere lonelier than the dark nothingness of space. Scott Parazynski is the author of The Sky Below: A True Story of Summits, Space, and Speed.

Scott Parazynski: Probably the most difficult thing I’ve ever done is ascend Mount Everest. That might come as a surprise; it’s very hard to become an astronaut, train for a mission, and go fly a mission, but the psychological difference of being on Mount Everest is pretty substantial.
When you’re in space you’re inside your spacecraft, you’re comfortable, you’re in short sleeves, it’s warm, you have three square meals a day, you’re not hypoxic, you’re not in malnourished. Up on Mount Everest every second of every day you’re feeling that: the thinning air, you can’t get enough calories in your body—you need 5000 or 6000 calories a day just to break even—and so you feel the life threat every minute of every day. There are avalanches that come calving down off the walls around the cirque of Everest base camp, so you feel that cumulative psychological stress of: you know you’re in a really dangerous place.

On a space shuttle mission in contrast you feel the threat obviously on the launch, you know, you’ve got seven million pounds of thrust taking you off of the planet, but then it’s very beautiful and peaceful, you’re in this extraordinary glass-bottom boat looking at your home planet and you feel like you’re the luckiest person alive. The only other time that you feel perhaps some degree of trepidation is floating outside that hatch and going out in the vacuum of space on a spacewalk, but for the most part being in space is just a peaceful, relaxing, disarming kind of a place, whereas the mental toll and the physical toll of Everest is pretty exceptional.

Certainly on Everest you’re out there more or less on your own, you have a small team, a cadre of folks that you’re with, and I had the good fortune to be with about 20 climbers on my team and my sidekick, Danuru Sherpa from Phortse, is just one of the amazing athletes and mountaineers in the world. He’s now summited Mount Everest 16 times. I used to joke with him all the time that he had three lungs and two hearts because he could just kind of run up most parts of Everest. Summit day, however, was a great equalizer, he was very much suffering just as much as I was, but you’re pretty much left to your own resources. No one can carry you down from summit day on Mount Everest, you’re going to do it under your own power or you’ll add to the 250 souls that are left on the side of the mountain, so it’s pretty sobering and you’ve got to have your wits about you.

I think that also weighs heavily in terms of the psyche of being high in the mountains versus being in space where you have this brilliant team of engineers and flight controllers in Houston and around the world kind of looking over your shoulder, and if things start to go south you know you’ve got the A-Team at your back.