A spacewalk, also called an EVA, is any activity an astronaut performs outside a spacecraft while in space. EVAs let crews repair equipment, install experiments, inspect hardware, and build large structures such as space stations. They matter because many spacecraft systems are too large, delicate, or unpredictable to service only from inside.
A spacewalk turns the astronaut into a small independent spacecraft, protected by a suit but exposed to vacuum, radiation, extreme temperatures, and orbital motion.
Before an EVA, astronauts use an airlock to move from cabin pressure to the low pressure inside the suit without emptying the whole spacecraft. They also prebreathe oxygen to remove nitrogen from the blood, reducing the risk of decompression sickness. During the EVA, safety tethers, handrails, foot restraints, and specialized tools keep the astronaut controlled while the spacecraft orbits Earth at about 7.7 km/s.
The main risks are suit failure, drifting away, fatigue, tool loss, micrometeoroid impacts, and the difficulty of working with bulky gloves in a vacuum.
Key Facts
- EVA means extravehicular activity, which is work performed outside a spacecraft.
- Orbital speed near the International Space Station is about v = 7.7 km/s.
- Pressure difference is ΔP = Pinside - Poutside, and outside pressure in space is nearly 0 Pa.
- Prebreathing oxygen lowers dissolved nitrogen in the body and helps prevent decompression sickness.
- A safety tether provides a physical connection so an astronaut cannot drift away from the spacecraft.
- Impulse from a tool or thruster follows J = Δp = mΔv, so even small pushes can change motion in microgravity.
Vocabulary
- EVA
- An EVA is an extravehicular activity, or any mission task performed by an astronaut outside a spacecraft.
- Airlock
- An airlock is a sealed chamber that lets astronauts move between cabin pressure and suit pressure without depressurizing the whole spacecraft.
- Prebreathing
- Prebreathing is the process of breathing pure oxygen before an EVA to remove nitrogen from the body.
- Safety tether
- A safety tether is a strong cord that keeps an astronaut or tool attached to the spacecraft during a spacewalk.
- Decompression sickness
- Decompression sickness is an injury caused by nitrogen bubbles forming in body tissues when pressure drops too quickly.
Common Mistakes to Avoid
- Thinking astronauts float because there is no gravity is wrong because they are in continuous free fall around Earth, with gravity still pulling strongly.
- Forgetting to account for prebreathing is wrong because moving too quickly from higher pressure to suit pressure can cause dangerous nitrogen bubbles.
- Assuming a loose tool simply stays nearby is wrong because in microgravity any small relative velocity can carry it away from the astronaut and spacecraft.
- Treating the tether as optional is wrong because it is a critical safety system that prevents an astronaut from drifting beyond reach if hand contact is lost.
Practice Questions
- 1 An astronaut and suit have a total mass of 150 kg. A small push changes the astronaut's speed by 0.04 m/s. What is the change in momentum?
- 2 A spacecraft orbits at 7.7 km/s. How far does it travel in 10 minutes? Give your answer in kilometers.
- 3 Explain why astronauts prebreathe oxygen before an EVA and why this step is especially important when the suit pressure is lower than the spacecraft cabin pressure.