In 1965, Ed White opened the hatch of his Gemini spacecraft and became the first American astronaut to go on a spacewalk, or Extra Vehicular Activity. No actual walking is involved in a spacewalk. We learned from the Gemini program that EVAs were not as simple as they looked; they required a lot of work and preparation.
Astronauts prepare for an EVA hours before putting on their spacesuits. They must breathe pure oxygen for a minimum of 40 minutes prior to depressurizing the airlock to prevent the bends. The air pressure in the suit is only a third of the air pressure in the space station, which is the same pressure (14.7 pounds per square inch) at sea level on Earth. When we go from high pressure to low pressure, nitrogen gas bubbles form in the blood flow and cause great pain in the joints. When we breathe pure oxygen, nitrogen is purged from the blood, preventing the painful bubbles.
Putting on the 275-pound suit requires a lot of exertion and help from fellow crewmembers. It takes about 15 minutes to get dressed in the liquid cooled undergarment, pants with boots, hard upper torso, gloves and helmet. Each piece of the suit is connected with complicated fasteners to prevent them from accidentally opening. Crew members help the astronaut get in the suit and fasten the sections.
After the astronauts are dressed, they close the inner hatch and depressurize the airlock. While their spacesuits are being pressurized, they check the systems on their suits and yawn and swallow to pop their ears. When the airlock is at a vacuum, they open the outer hatch and exit into space where they can work for about seven hours.
You can become an astronaut in training and experience what it would be like to live and work in zero gravity at Carnegie Science Center's new SpacePlace exhibit.