Space Station Extravehicular Activity

Working Outside the International Space Station

STS-104 Astronaut James F. Reilly poses for a photo in the Quest Joint Airlock Module at the completion of the final STS-104 spacewalk, which was the first conducted from Quest.

Before the arrival of the Joint Airlock Module, which is named Quest, on shuttle mission STS-104, spacewalks conducted from the space station could only use Russian spacesuits, unless the space shuttle was present. The Zvezda Service Module provides a capability for station-based Russian spacewalks using only Russian spacesuits. The Joint Airlock Module, which was attached to the station during the 10th space shuttle assembly flight, gave the station the capability to conduct spacewalks using U.S. spacesuits.

Quest, which has the capability to be used by both Russian and U.S. spacesuit designs, consists of two sections: a "crew lock" that is used to exit the station and begin a spacewalk and an "equipment lock" used for storing gear.

The station crew can also perform spacewalks in Russian Orlan spacesuits from the Russian Docking Compartment, named Pirs.

Astronaut Daniel Barry wears a training version of the extravehicular mobility unit (EMU) spacesuit during an underwater simulation of a spacewalk for the ISS-2A.1 mission.

Spacewalkers must wear pressurized spacesuits in order to work in space. These suits have pressures significantly lower than ambient cabin pressure of a spacecraft. This makes spacewalkers subject to decompression sickness, more commonly known as the "bends." Decompression sickness results from nitrogen bubbles forming in the tissues or blood stream and moving to other areas of the body. Therefore, spacewalking crewmembers must perform a pre-breathe protocol, which is designed to wash out any excess nitrogen from the body, before a spacewalk. This protocol takes advantage of the fact that exercise increases the speed at which nitrogen is removed from the body by increasing blood circulation through the extremities. The ISS pre-breathe protocol involves breathing pure oxygen for a total of 2 hours and 20 minutes and includes a short period of high-intensity exercise at the beginning of the pre-breathe procedure.

Station astronauts begin the pre-breathe protocol by exercising vigorously on the space station's cycle ergometer for a total of 10 minutes while breathing pure oxygen via an oxygen mask. After 50 total minutes of breathing pure oxygen, including the 10 minutes initially spent exercising, the pressure in the station's airlock will be lowered to 10.2 pounds per square inch, or psi. During airlock depressurization, the spacewalkers will breathe pure oxygen for an additional 30 minutes. At the end of those 30 minutes, with the airlock now at 10.2 psi, the spacewalkers will put on their space suits. Once their spacesuits are on, the spacewalkers will breathe pure oxygen inside the suits for an additional 60 minutes before making final preparations to leave the station and begin their spacewalk. This protocol provides a total of 2 hours and 20 minutes of pre-breathe time, including the 10 minutes of vigorous exercise at the beginning of the procedure.

With the operational Joint Airlock Module, the philosophy of spacewalk training will shift due to the increasing complexity of the station and the ability of the station crew to perform spacewalks. Rather than attempting to train station crew members for every EVA task they may be called upon to perform during a mission, training will increasingly aim toward providing crew members with a general suite of EVA skills. The station's growing size and complexity will make it virtually impossible for astronauts to train for every possible contingency and maintenance EVA, as is the case in training for shuttle missions.