Extravehicular activity (EVA) is any operation in which a crew member leaves the pressurized volume of a vehicle to work in the vacuum of space and then returns. In everyday language an EVA is often called a "spacewalk" and typically refers to work outside a vehicle orbiting a body. The person who performs an EVA is commonly an astronaut or cosmonaut who exits a spacecraft to operate in outer space or on a surface such as the Moon. Many EVAs take place around Earth, but surface excursions and deep-space activities are part of exploration planning.

Core characteristics and equipment

EVAs require specialized life‑support systems and procedures. A pressurized suit provides breathable gas, thermal regulation, micrometeoroid shielding and communications; examples for orbital work include variants of the U.S. Extravehicular Mobility Unit (EMU) and the Russian Orlan systems. Safe transfer between cabin and vacuum is usually through an airlock or suitport, and tethers, handrails and restraints reduce the risk of uncontrolled drift. Crews use tools designed for gloved hands and may carry short‑range propulsion devices for emergency return.

History and development

Early EVAs proved humans can work outside spacecraft and led to more complex tasks: lunar surface exploration during the Apollo program, construction and maintenance of large orbital platforms, and routine station operations. The first human EVA was conducted by a Soviet cosmonaut and the first American EVA followed soon after; later missions extended duration and operational complexity. The Apollo missions also included surface walks and, in a few cases, spacewalks during return phases. Major national programs with recorded EVA activity include Russia, the United States and China, and international crews have performed EVAs on cooperative platforms like the International Space Station. The Apollo program (often cited as Apollo (4920) in some archives) remains a key chapter in EVA history.

Typical uses and notable examples

  • Assembly and construction: joining modules, installing trusses and deploying large structures.
  • Maintenance and repair: servicing instruments and telescopes, replacing components.
  • Scientific fieldwork: geological sampling and experiments on planetary surfaces.
  • Emergency operations: restoring critical systems, retrieving objects, or performing contingency repairs.

Famous milestones include the first human steps on the lunar surface, the numerous station assembly EVAs that built orbital complexes, and high‑profile repairs such as those performed on space telescopes. EVAs have enabled long‑term human presence and scientific return beyond what can be achieved from inside a vehicle alone.

Risks, procedures and training

Working in vacuum presents hazards: extreme temperature swings, radiation, suit punctures or leaks, decompression sickness and the consequences of becoming untethered. To mitigate these risks, crews follow decompression and prebreathing protocols, use redundant systems and tethers, rehearse tasks extensively in neutral buoyancy pools and simulators, and carry contingency gear such as emergency propulsion units. Detailed timelines, checklists and close ground–crew coordination are standard practice.

Variants and future directions

EVAs vary by context: station maintenance EVAs emphasize tethering and modular tasks, lunar or planetary surface EVAs emphasize mobility, dust mitigation and field science, and untethered operations require reliable propulsion and navigation. Future exploration missions plan to expand surface EVA capabilities, refine suit designs for mobility and dust tolerance, and develop protocols for longer, more autonomous excursions. For mission summaries, training material and historical records, consult agency resources and published mission archives using mission names and dates as reference.