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How do satellites stay in orbit?

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Quick answer

A satellite is constantly pulled toward Earth by gravity, but it is also moving sideways very fast. Gravity bends its path into a curve, and if the speed is right, the curve matches Earth's own curvature, so the satellite keeps falling around the planet rather than into it.

A satellite stays in orbit because its sideways speed is high enough that, as gravity pulls it downward, the curved surface of the Earth falls away beneath it at the same rate. It is continuously falling toward Earth but moving sideways fast enough to keep missing it.

Step by step

  1. A rocket lifts the satellite above most of the atmosphere and gives it a large horizontal speed.
  2. Gravity pulls the satellite toward Earth's centre, bending its straight-line path into a curve.
  3. The satellite moves sideways while falling, so the ground curves away beneath it at the same rate.
  4. With the correct speed for its altitude, the satellite completes a closed loop and keeps repeating it.
  5. Small thrusters occasionally adjust the orbit to counter drag or slight gravitational tugs.

Key things to understand

  1. Gravity pulls a satellite toward Earth's centre at every moment, bending its path into a curve.
  2. The satellite also has a large sideways (tangential) velocity from the rocket that launched it.
  3. These two effects combine so the satellite falls toward Earth while the ground curves away below it.
  4. At the right speed, the fall matches the curvature of Earth, producing a closed orbit.
  5. Too slow and it dips into the atmosphere; faster gives a stretched ellipse, and above escape speed it leaves Earth.

Labelled diagram

  1. Launch

    Rocket carries the satellite above the thick atmosphere and gives it sideways speed.

  2. Gravity pull

    Earth's gravity constantly pulls the satellite toward the planet's centre.

  3. Sideways motion

    The satellite's high tangential velocity carries it forward as it falls.

  4. Curved path

    Gravity bends the forward motion into a curve around Earth.

  5. Closed orbit

    At the right speed, the curve matches Earth's surface and repeats endlessly.

How a satellite stays in orbit

Real-world examples

  • The International Space Station orbits about 400 kilometres up and circles Earth roughly every 90 minutes.
  • Geostationary weather and communication satellites sit about 36,000 kilometres above the equator and match Earth's rotation.
  • The Moon orbits Earth at about 384,000 kilometres, taking roughly 27 days for one revolution.
  • Navigation satellites such as those in GPS constellations are placed in medium Earth orbits so their signals cover the whole planet.

Common mistake

✗ Myth: Satellites float in space because there is no gravity up there.

✓ Fact: Gravity extends far into space and is what holds satellites in orbit. Astronauts and satellites appear weightless because they are in continuous free fall around Earth, not because gravity has disappeared.

People also ask

What speed does a satellite need to stay in orbit?
For a low Earth orbit a few hundred kilometres up, the required sideways speed is about 7.8 kilometres per second, roughly 28,000 kilometres per hour. At that speed the curve of the falling path matches Earth's curvature, so the satellite keeps circling instead of dropping to the ground.
Why do satellites in low orbit eventually fall back to earth?
At low altitudes a tiny amount of air still exists, and it creates drag that slowly steals the satellite's speed. As speed drops, the orbit shrinks and the satellite descends lower, where the air is thicker. This runaway effect eventually pulls it into the atmosphere, where it burns up.
What happens if a satellite goes too fast or too slow?
Too slow, and its curved path dips into the atmosphere, where drag brings it down. Somewhat faster than circular speed, it follows a stretched ellipse that climbs higher; above escape speed, about 11 kilometres per second near Earth, it leaves Earth entirely.
Why do satellites not fall back to Earth?
They are falling, but they are also moving sideways fast enough that they keep missing the ground. Gravity bends their path into a curve that matches Earth's curvature, so they circle instead of landing.
What keeps a satellite moving if there is no air in space?
Nothing slows it down, so it keeps moving. In the near-vacuum of low Earth orbit there is almost no air drag, and no force is needed to maintain constant velocity. Only slight atmospheric drag gradually lowers very low orbits.
What is the difference between low Earth orbit and geostationary orbit?
Low Earth orbit is a few hundred kilometres up, where satellites circle in about 90 minutes. Geostationary orbit is about 36,000 kilometres up, where one orbit matches Earth's rotation, about 23 hours 56 minutes, so the satellite appears fixed over one point on the equator.
Do satellites need fuel to stay in orbit?
Not to keep circling, because gravity and their speed do that. They do carry small thrusters to correct their orbit when drag or slight gravitational variations push them off course, and to change position when needed.

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