On March 18, 1965, Soviet cosmonaut Alexei Leonov became the first human to leave a spacecraft and float in open space. His 12 minute 9 second spacewalk outside Voskhod 2 proved that astronauts could work beyond the protection of a cabin. This mattered because future missions would need people to inspect spacecraft, repair equipment, assemble structures, and explore the Moon.
The event also showed that spacewalking is not simple floating, but a demanding operation involving pressure, motion, life support, and risk.
Understanding Astronautics: The First Spacewalk
A spacewalk begins long before the hatch opens. The crew moves into an airlock, a small chamber between the cabin and space. Air is removed gradually so opening the outer hatch does not empty the whole spacecraft.
The astronaut breathes pure oxygen at reduced pressure before going outside. This process lowers the risk of decompression sickness, in which dissolved gases form dangerous bubbles in the blood.
Modern crews spend hours preparing their bodies, tools, checklists, and handholds. Every item must be secured because a loose object can drift away or strike equipment.
A spacesuit is a personal spacecraft. It supplies oxygen, removes carbon dioxide, controls temperature, provides communications, and protects the body from vacuum. Vacuum does not pull a person apart, but it removes the outside pressure that normally balances pressure inside the body.
The suit must hold its shape against this difference. Pressure acting over a large area creates a large outward force, so a suit tends to become stiff when pressurized. This made early suits difficult to bend.
Leonov's suit expanded enough to limit his movement, making it hard for him to return through the narrow airlock. He had to reduce suit pressure carefully before he could get back inside.
An astronaut outside a spacecraft is still orbiting Earth at nearly the same speed as the spacecraft. They are not beyond gravity. Both astronaut and spacecraft are continuously falling toward Earth, but their sideways motion carries them around the planet.
Small pushes matter because there is almost no air resistance to slow motion down. Pushing off a rail sends the astronaut in the opposite direction. Turning a tool can make the astronaut rotate in return.
A tether prevents separation, yet it can become twisted or snagged. Crews use handrails, foot restraints, and planned body positions to control these effects. The tether can pull taut and exert tension, but it is not a rigid path that automatically keeps someone still.
Spacewalk work is demanding because the environment changes what ordinary actions feel like. In sunlight, surfaces can become extremely hot. In shadow, they can become extremely cold.
A visor must reduce bright sunlight while preserving a clear view of tools and displays. Gloves protect hands, though thick gloves reduce touch and tire the muscles. Water cooling inside the suit carries away body heat, since sweat cannot cool the body effectively in vacuum.
Students learning this topic should connect several ideas rather than treating a spacewalk as one event. Pressure explains suit design. Newton's laws explain motion near the spacecraft.
Heat transfer explains temperature control. Careful procedures link all of these physics ideas to human safety.
Key Facts
- First human spacewalk: Alexei Leonov, Voskhod 2, March 18, 1965.
- Duration of Leonov's EVA: 12 min 9 s = 729 s.
- Orbital speed near low Earth orbit is about v = 7.8 km/s.
- For circular orbit, gravitational force supplies centripetal force: GMm/r^2 = mv^2/r.
- A tether provides a safety connection and can exert tension, modeled as F = T along the tether.
- Pressure difference creates force on a surface: F = P A.
Vocabulary
- EVA
- EVA means extravehicular activity, which is any astronaut activity performed outside a spacecraft.
- Tether
- A tether is a strong line that connects an astronaut to a spacecraft to prevent drifting away.
- Airlock
- An airlock is a sealed chamber that lets people move between a pressurized spacecraft and the vacuum of space.
- Pressure suit
- A pressure suit is a wearable life-support system that keeps a human body under safe pressure in space.
- Low Earth orbit
- Low Earth orbit is a region a few hundred kilometers above Earth where spacecraft travel fast enough to keep falling around the planet.
Common Mistakes to Avoid
- Thinking a spacewalking astronaut is weightless because there is no gravity is wrong because gravity is still strong in low Earth orbit and both astronaut and spacecraft are continuously falling around Earth.
- Forgetting the pressure suit can stiffen in vacuum is wrong because internal suit pressure pushes outward and can make bending arms, legs, and gloves difficult.
- Assuming a tether pulls an astronaut back automatically is wrong because a tether only provides a force when it becomes taut or is actively reeled or pulled.
- Treating the first spacewalk as routine is wrong because Leonov's suit expanded, reentry procedures became difficult, and the crew faced serious life-support and landing hazards.
Practice Questions
- 1 Leonov's spacewalk lasted 12 min 9 s. Convert this time to seconds, then find how far Voskhod 2 traveled during the EVA if its orbital speed was 7.8 km/s.
- 2 A circular spacecraft hatch has area 0.50 m^2. If the pressure difference across it is 40,000 Pa, what force does the pressure difference exert on the hatch? Use F = P A.
- 3 Explain why Leonov could float beside Voskhod 2 without falling behind it, even though both were moving around Earth at several kilometers per second.