What is Extravehicular Activity (EVA)?

Extravehicular Activity (EVA) refers to any activity where an astronaut leaves the safety of a spacecraft to work in outer space. EVAs are commonly called “spacewalks.”

  • Purpose: Maintenance, repair, scientific experiments, construction (e.g., International Space Station).
  • Environment: Microgravity, vacuum, extreme temperatures, radiation.

Historical Context

Early Milestones

  • First EVA: Alexei Leonov (Soviet Union), March 18, 1965, spent 12 minutes outside his spacecraft.
  • First American EVA: Ed White, Gemini IV, June 1965.
  • Moonwalks: Apollo missions (1969–1972) involved EVAs on the lunar surface.

Evolution

  • Space Shuttle Era: EVAs for satellite repair, ISS assembly.
  • International Space Station (ISS): Routine EVAs for maintenance and upgrades.

EVA Equipment

Spacesuit (Extravehicular Mobility Unit - EMU)

  • Layers: Protection against temperature extremes, micrometeoroids, radiation.
  • Life Support: Oxygen supply, CO₂ removal, temperature regulation.
  • Mobility: Joints and bearings for movement.

Safety Features

  • Tether: Prevents astronauts from drifting away.
  • Communication System: Helmet radio for talking with crew and mission control.

Tools

  • Handrails: For stability.
  • Specialized tools: Wrenches, power drills, cameras.

EVA Procedures

  1. Preparation: Suit up, check systems, pre-breathe oxygen to avoid decompression sickness.
  2. Airlock: Transition from spacecraft to vacuum.
  3. Spacewalk: Perform tasks, stay tethered, monitor suit status.
  4. Return: Re-enter airlock, repressurize, remove suit.

Mind Map

EVA Mind Map

Risks and Challenges

  • Radiation Exposure: No atmosphere for protection.
  • Temperature Extremes: -250°F to +250°F.
  • Micrometeoroids: High-speed particles can puncture suits.
  • Fatigue: Physical exertion in bulky suits.
  • Communication Delays: Signal lag with mission control.

Ethical Issues

  • Astronaut Safety: Balancing mission needs with personal risk.
  • Resource Allocation: High cost of EVAs—should resources go to robotic alternatives?
  • Environmental Impact: Space debris creation during EVAs.
  • Access and Equity: Who gets to perform EVAs? Gender, nationality, and training opportunities.

Recent Research

A 2022 study published in npj Microgravity (“Physiological and psychological effects of extravehicular activity on astronauts,” npj Microgravity, 2022) found that EVAs can cause significant physiological stress, including cardiovascular strain and muscle fatigue. The study suggests new suit designs and pre-EVA exercise protocols to reduce health risks.

Surprising Facts

  1. Water Recycling: The water astronauts drink on the ISS is recycled from sweat, urine, and humidity. The water you drink today may have been drunk by dinosaurs millions of years ago, as Earth’s water is constantly recycled.
  2. Space Suit Weight: On Earth, a spacesuit weighs over 125 kg (275 lbs), but in microgravity, it feels weightless.
  3. Longest EVA: The longest spacewalk lasted 8 hours and 56 minutes (NASA astronauts Jim Voss and Susan Helms, 2001).

Diagrams

Spacesuit Layers

Spacesuit Layers Diagram

EVA Timeline

EVA Timeline

Key Terms

  • Microgravity: Very weak gravity, as in orbit.
  • Airlock: Chamber for entering/exiting spacecraft.
  • Tether: Safety line connecting astronaut to spacecraft.
  • Radiation: Energy from the sun and space, harmful to humans.

Conclusion

Extravehicular Activity is a complex, risky, and essential part of human space exploration. It requires advanced technology, careful planning, and ethical consideration to ensure safety and success. Ongoing research continues to improve EVA procedures and equipment for future missions to the Moon, Mars, and beyond.

References

  • npj Microgravity (2022). “Physiological and psychological effects of extravehicular activity on astronauts.” Link
  • NASA EVA Factsheets and ISS Operations Data