(Not) Freezing in Space

July 2016

Author Marianne Dyson‘s Science Snacks Newsletter


Caption: In March 1965, Russian Alexei Leonov (1934–) nearly died during the first ever spacewalk. (Image from “The Moon,” original Russian title ЛУНА, 1965)

(Not) Freezing in Space

A young man who attended my presentation “Your Future Space” at the Tyler Junior College Planetarium June 25 asked if astronauts are in danger of freezing during spacewalks.

The temperature in space is about 250 degrees F (121 C) in the sun, and about -250 degrees F (-157 C) in the “shade.” But the real danger of freezing is not from the cold. A body exposed to vacuum, in the sun or shade, will freeze-dry as all the air and liquids boil away.

However, astronauts are much more likely to overheat than freeze because spacesuits and space vehicles are insulated and sealed to prevent exposure to vacuum. (See NASA’s “Staying Cool on the ISS.”)

In fact, the first spacewalker, Russian Alexei Leonov, almost died of heatstroke. Like a sealed snack bag taken on up an airplane, his spacesuit ballooned out. Bending fingers, arms or legs against this pressure requires tremendous strength. Leonov had to release air from the suit to bend enough to get through the hatch and then close it.


Caption: At 11.500 feet in our Cessna 182 (see altimeter), the air trapped in the potato chip bag expands outward because the air in the cockpit presses on the bag about 35 percent less than at sea level. This ballooning effect is even more pronounced in the vacuum of space. (Photo by Marianne Dyson.)

Leonov perspired so much that once on the ground, “his sweat was now sloshing around in the suit, up to his knees.” (See BBC’s “The First Spacewalk.”)

Modern-day spacesuits use a lower pressure and don’t balloon out as much as Leonov’s did, and they fit through the hatches just fine. But astronauts still work up a sweat. As Scott Parazynski noted in an interview, “It takes quite a bit of effort [to move] … When you’re moving a spacesuit that is fully loaded with tools, and your own personal bodyweight, and the things you have in your backpack, it’s about 630 pounds’ worth of mass.” (Gwynne Watkins, “An Astronaut Fact-checks Gravity.”)

To stay cool, spacewalkers wear special long underwear filled with about 300 feet (91 m) of water-filled tubes. Astronauts can stop the flow if they get too cold. (Space Station Science, page 81).

People and equipment produce a lot of waste heat that builds up inside spacecraft as well. To keep spacecraft from overheating, fans blow hot air over cold tubes of water in what is called a heat exchanger. The water tubes are then cooled by ammonia in another heat exchanger. (Because ammonia is toxic, heat is not transferred directly from the air to the ammonia.) The giant white radiator panels on the International Space Station are filled with tubes of ammonia that radiate their heat into space.

So though there is a danger of freezing in space because of the vacuum. But spacesuits and spacecraft are designed to keep the air, and astronauts, comfortably cool.

Writing about Space

My story, “Fireworks in Orbit,” is about what might have happened if the space shuttle’s cooling system failed during a spacewalk. Originally published in Analog, it is reprinted in Fly Me to the Moon and Other Stories, available via CreateSpace or as an eBook via Amazon. For autographed copies, visit my website or find me at one of the events below.

Speaking about Space

Look for me at the following events. Watch my website Contact page for updates & Twitter for photos.

Friday, July 15, 5 pm to closing. Signing A Passion for Space, Welcome to Mars, & Home on the Moon at Barnes & Noble Westheimer Crossing, 7626 Westheimer (Galleria), Houston, TX 77063.

August 17-21, MidAmeriCon II, the 74th Science Fiction Worldcon, Kansas City, MO. I’m moderating “The Real Martians” panel at 4 pm Friday.

Author: Marianne

Marianne Dyson is an award-winning children's author, science fiction writer, and former NASA flight controller. To invite her to speak or order her books, visit her website, www.MarianneDyson.com.