What is the ISS?
The International Space Station is a large spacecraft where astronauts live, work, and do science in orbit around Earth.
The ISS is a real spacecraft, not a building in the sky. It travels around Earth while crews live inside it for months at a time.
It is also a science laboratory. Astronauts use the station to study how people, plants, fluids, materials, and equipment behave in space.
The station is made from connected pressurized modules, solar arrays, docking ports, robotic arms, radiators, and external equipment.
Mini facts
- It is a laboratory in space.
- It orbits Earth many times per day.
- It has modules, solar arrays, docking ports, radiators, and external equipment.
Did you know?
The ISS shows how engineering, science, and international teamwork can keep people living safely in orbit for long periods.
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How fast is the ISS?
The ISS moves fast enough to circle Earth roughly every 90 minutes.
The station travels at orbital velocity. It is much faster than an airplane and crosses oceans and continents in minutes.
It is not fixed above one city. Its ground track shifts because Earth rotates underneath while the station keeps moving around the planet.
The exact speed and altitude are part of the live shown in the tracker. These values change slightly as the orbit is maintained.
Mini facts
- One orbit takes roughly 90 minutes.
- The ISS completes about 16 orbits per day.
- The path over Earth changes from orbit to orbit.
Fast fact
Knowing the speed helps explain why the ISS can pass over your sky quickly and why crews see many sunrises each day.
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Why does the ISS not fall down?
Gravity pulls on the ISS, but its forward speed makes it keep missing the ground.
The ISS does not stay up because gravity disappears. Gravity still pulls on the station and everything inside it.
The key is . The station is constantly falling toward Earth, but it also moves forward so fast that Earth curves away beneath it.
That balance of falling and forward motion is why the ISS keeps moving around Earth instead of dropping straight down.
Mini facts
- Gravity still acts on the ISS.
- The station is falling around Earth.
- Forward speed keeps it missing the ground.
Common misconception
Orbit is one of the most important ideas in spaceflight. It explains satellites, crewed spacecraft, and how the tracker map changes.
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Orbit check-in
Try these before the final quiz. Each tap gives immediate feedback.
True or false: the ISS floats because there is no gravity.
True or false: the ISS completes one orbit in roughly 90 minutes.
True or false: the ISS stays above the same city all day.
Why do astronauts float?
Astronauts float because the ISS and everything inside it are in continuous free fall together.
Floating inside the station is not true zero gravity. Gravity is still present in orbit, but the station, astronauts, tools, food, and water are all falling together.
This creates , where people and objects seem weightless because there is no floor pushing up on them the way it does on Earth.
Astronauts use handrails, foot loops, and careful routines so floating is useful instead of chaotic.
Mini facts
- Microgravity is not true zero gravity.
- Everything inside falls around Earth together.
- The effect makes people and objects float.
Common misconception
Microgravity changes human bodies and experiments, which is why the station is valuable for science and why crews must exercise every day.
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What happens inside the ISS?
Inside the ISS, astronauts live through highly planned days of science, maintenance, exercise, meals, sleep, and communication with Earth.
Crew members sleep in small crew quarters, eat carefully prepared food, and use equipment designed for a floating environment.
They spend much of the day running experiments, repairing equipment, checking station systems, and talking with mission control teams on Earth.
Exercise is part of the workday because muscles and bones weaken in .
Mini facts
- Astronauts sleep, eat, exercise, work, and communicate with Earth.
- Maintenance is part of station life.
- Daily routines are carefully scheduled.
Why it matters
The station is both a home and a workplace, so daily routines are designed to keep crews healthy and the spacecraft operating safely.
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What science happens there?
The ISS lets scientists study systems that behave differently when gravity is greatly reduced.
Research on the station includes biology, human health, physics, fluids, materials, plant growth, Earth observation, and technology testing.
In microgravity, flames, liquids, cells, crystals, and muscles can behave differently. Scientists use those differences to ask questions that are difficult to study on Earth.
The station also looks back at Earth, helping people observe storms, coastlines, cities, fires, glaciers, and the atmosphere.
Mini facts
- Human health research studies bodies in space.
- Plant and biology experiments test life in microgravity.
- Earth observation connects space science to our planet.
Why it matters
ISS research helps prepare future space missions and can also improve medicine, materials, technology, and Earth observation.
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How do spacecraft dock?
Crew and cargo spacecraft connect to docking ports on the ISS with careful guidance and precise control.
Visiting spacecraft bring astronauts, food, water, experiments, equipment, and supplies. Some vehicles carry crew, while others are built mainly for cargo.
A approach must be slow and accurate. The spacecraft lines up with a docking port, connects mechanically, and then the connection is checked before hatches open.
Docking ports are part of the station's traffic system. They let the ISS receive visitors and supplies without landing back on Earth.
Mini facts
- Crew and cargo spacecraft visit the ISS.
- Docking ports connect vehicles to the station.
- Docking is precise and carefully controlled.
Fast fact
Docking keeps the station supplied and makes crew rotation possible, turning the ISS into a continuously operating outpost.
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What are spacewalks?
A spacewalk is work outside the station in a spacesuit.
A spacewalk is also called an . During an EVA, astronauts leave the safety of the station's inside modules.
Spacewalks are used for repairs, upgrades, inspections, equipment installation, and some experiments. Astronauts are connected to the station and supported by teams on Earth.
EVAs are carefully planned because they are difficult and dangerous. Spacesuits must provide oxygen, cooling, communication, pressure, and protection.
Mini facts
- EVA means extravehicular activity.
- Astronauts work outside in spacesuits.
- Spacewalks support repairs, upgrades, inspections, and experiments.
Why it matters
Spacewalks let crews maintain and improve the station when robotic arms or internal repairs are not enough.
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