On Earth, the atmosphere and the magnetosphere protect us from many different, dangerous things from space. In space, astronauts are exposed to many expected and unexpected dangers. Lack of oxygen probably comes to mind first. But there are many other unexpected and life-threatening surprises. When astronauts go into space, their spacecraft and spacesuits help protect them from atmospheric pressures and from temperature changes. There is no protection from radiation, high-energy protons, heavy ions, or cosmic rays.

Cosmonaut Aleksei Leonov was the first man to “walk” in space outside his space capsule Voskhod 2 on March 18, 1965. His newly designed space suit expanded after he went out the hatch. The flexible, pressurized material expanded like a balloon, and Leonov couldn’t get back into the spacecraft through the hatch. He released some of the internal pressure, but the suit wouldn’t shrink enough. Before the pressure got low enough to make him unconscious, he squeezed back in through the hatch.

On the moon, unprotected skin in shadow freezes because of the -250 degree F temperature. But unprotected skin in direct sun would be exposed to ultraviolet-C that would cause severe burns, and UV-B rays more than 250 times stronger than on Earth would blister the skin in 14 seconds.

Water boils at lower temperatures in lower air pressures. In the “mile-high” city of Denver, Colorado in the Rocky Mountains, water boils at a temperature 10 degrees cooler than at the sea level city of Boston, Massachusetts. Because the air pressure is lower in the mountains than at sea level, water boils faster. That’s why many recipes give different baking instructions for people living at higher altitudes and lower air pressures.+
A critical altitude is at 63,000 feet and is called Armstrong’s Line. At 63,000 feet above sea level, water’s boiling point is the body’s temperature, 98.6 degrees F. All liquid parts of the body, like blood, boil automatically at that altitude. In space, liquids can boil from the air pressure and freeze from the temperature at the same time!

Three cosmonauts died from this in 1971. Their space capsule vent popped open while they were still in space. All the air inside the capsule leaked out. The lower pressure boiled their blood and they died.