What Is a Spacewalk? Learn Why Astronauts Perform Spacewalks and How Astronauts Train for Spacewalks

In an astronaut spacewalk, also known as an Extra Vehicular Activity (EVA), an astronaut literally walks in space, exiting the relative safety of the international space station in order to perform exterior repairs on things like a solar panel. Spacewalks are dangerous, physically demanding, and rare.

The process of doing a spacewalk is not just physically challenging due to the pressurized resistance of the suit, it is also mentally demanding—astronauts have to focus on the work they are doing as well as their safety, a vast number of potential tools, interacting with the crew and with the team down in mission control, all while the clock is ticking.

American, Russian, and European, and Canadian astronauts such as Chris Hadfield and David Saint-Jacques have all performed spacewalks. Recently, female astronauts Anne McClain and Cristina Koch completed their first spacewalks, though the opportunity for the first American all female spacewalk was missed because of issues with spacesuit sizes, meaning NASA Astronaut Anne McClain walked with astronaut Nick Hauge.

Spacewalking is dangerous and only performed when a job requires the skill and dexterity of a human—something that can’t be done by a robot.

The vast majority of astronauts’ work is done inside the relatively safe environment of the spaceship, and they use robotic arms like Canadarm2 to remotely do work outside in the harsh thermal vacuum. Occasionally, though, external work needs to be done that requires direct human judgment or dexterity. When the need outweighs the risk, a spacewalk is planned.

There are many different reasons for spacewalking—everything from installing a new piece of equipment or removing a broken piece of apparatus, to deploying experiments, to surveying for damage—but the operational components of a spacewalk are all the same regardless of task.

In the international space station, astronauts must exit the space center through the pressure-controlled Quest Airlock. Once in space, there are systems in place to ensure its efficacy and safety:

• During a spacewalk, astronauts are supported by the crew inside the station, who help to remind them where they are in the procedure or setting for the tools they are using.
• Astronauts have to work through their tasks with only an emergency checklist, as there is no practical way to carry a printed set of instructions.
• Astronauts are reliant on their crew and a spacewalk-experienced astronaut down on the ground to support them through the procedures.
• If an astronaut is the lead spacewalker, they are also responsible for keeping track of what the other astronaut is doing outside, as well as the cadence, safety, and completion of the entire extravehicular activity.

The EVA spacesuits are the most important component to ensuring astronaut safety during a spacewalk.

• EVA spacesuits are designed to protect astronauts from the hostile, deadly environment of space. The spacewalk spacesuit shirt consists of a hard upper torso to protect vital organs from debris and other dangers.
• They are pressurized with pure oxygen to one-third of sea-level pressure, can withstand the extreme cold and heat of the vacuum, and protect astronauts from the constant bombardment of tiny, high-speed micrometeoroids that fly through the solar system at 10 kilometers per second.
• The suit has a portable life-support system in its backpack. It contains the oxygen-purification system, cooling system, radio, and lithium ion battery power system.
• On the helmet, there are cameras so that mission control can get a visual record of work astronauts carry out, as well as lights for working in the dark. It also has a gold visor and sunshields to protect an astronaut’s face and eyes from the incredibly harsh, unfiltered solar array.
• On the chest there is a computer display and control module to run the suit and a purge valve to dump pressure if needed.
• Two hard clips on the front of the suit allow astronauts to attach a metal frame that holds all tools.
• During a spacewalk, astronauts keep themselves connected to the space station with at least one tether, clipped to the suit using locking metal hooks.
• Spacesuits are white to reflect the heat from the sun. The suit itself consists of 14 layers of material, with each layer playing a different role in keeping astronauts alive.

Before you do a spacewalk there are years of training on suit systems, in virtual reality simulators, in vacuum chambers, and simulating weightlessness under water. The most important of these training environments is underwater because the environment on Earth that best simulates the weightlessness of spacewalking is under water.

• NASA astronauts train at the Neutral Buoyancy Laboratory at the Johnson Space Center. In this facility there is a 45-foot-deep pool, which contains a replica section of the ISS and the Canadarm2, used to help practice the choreography of a spacewalk.
• The main aim of training is to invent, develop, and perfect entire EVAs, and hone the individual skills needed.
• Astronauts spend hundreds of hours training under water, learning how to operate and maneuver in their spacesuit, learning how to think in three dimensions, and developing new techniques for spacewalking.
• During training, you practice the skills to monitor the health of your suit, get used to the cadence of hot sunrises and frigid, dark sunsets every 46 minutes, and prepare for the physically demanding experience of spacewalking, as the pressurized, stiff suit resists every motion.
• You train and prepare to the point that when you are carrying out an actual spacewalk, the experience is not overwhelming, but hopefully familiar and efficient.

Astronauts also must learn and qualify on SAFER (Simplified Aid for EVA Rescue).

• SAFER is a jetpack, used as an emergency self-rescue system in the event that you were to detach from the ISS and go tumbling into space.
• It is operated by a deployable joystick that fires puffs of nitrogen gas through 24 small nozzles to stop you from tumbling, and help steer astronauts back to grab onto the station.

Learn more about space exploration in former astronaut Chris Hadfield’s MasterClass.