Astronauts live in space by turning a spacecraft into a carefully controlled habitat for the human body. In orbit, they experience microgravity, limited space, recycled air, and a closed water supply. Daily tasks like eating, sleeping, washing, and exercising must be redesigned so people can stay healthy and keep the station working.
Understanding space life shows how physics, biology, and engineering combine in one extreme environment.
The International Space Station orbits Earth about every 90 minutes, so astronauts see many sunrises and sunsets each day. Because falling objects, people, and the station all fall around Earth together, astronauts feel weightless even though gravity is still present. Life support systems remove carbon dioxide, add oxygen, control temperature, and recycle water from humidity and urine.
Exercise machines, Velcro, foot loops, sealed food packets, and careful schedules help astronauts live and work safely in microgravity.
Key Facts
- Astronauts in low Earth orbit are in free fall around Earth, which creates apparent weightlessness.
- Orbital speed of the ISS is about 7.7 km/s, or about 28,000 km/h.
- The ISS completes one orbit in about 90 minutes, giving astronauts about 16 sunrises per Earth day.
- Weight is W = mg, but apparent weight can be near zero during continuous free fall.
- Life support systems must control O2, remove CO2, regulate temperature, and recycle water.
- Astronauts exercise about 2 hours per day to reduce bone loss and muscle weakening in microgravity.
Vocabulary
- Microgravity
- Microgravity is the condition in which objects appear almost weightless because they are falling together in orbit.
- Free fall
- Free fall is motion under the influence of gravity alone, without support from a floor or surface.
- Life support system
- A life support system is equipment that keeps astronauts alive by managing air, water, temperature, and waste.
- Orbit
- An orbit is the curved path an object follows around a planet, moon, or star because of gravity.
- Apparent weight
- Apparent weight is the support force a person feels from a surface, which can become nearly zero in orbit.
Common Mistakes to Avoid
- Saying there is no gravity in space is wrong because gravity still pulls strongly on the ISS and keeps it in orbit around Earth.
- Thinking astronauts float because they are far from Earth is wrong because the ISS is only a few hundred kilometers above the surface and is still in Earth's gravitational field.
- Forgetting that water forms blobs in microgravity is wrong because fluids do not pour downward normally without a strong apparent weight.
- Assuming astronauts do not need exercise is wrong because muscles and bones weaken when the body does not have to support its weight.
Practice Questions
- 1 The ISS orbits Earth once every 90 minutes. How many complete orbits does it make in 24 hours?
- 2 An astronaut has a mass of 75 kg. What is the astronaut's weight on Earth using W = mg and g = 9.8 m/s^2?
- 3 Explain why an astronaut floats inside the space station even though Earth's gravity is still acting on both the astronaut and the station.