十万个为什么·科学启蒙30篇（4）
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Why Satellites Orbit Earth Without Falling Down
为什么卫星能绕地球运行不掉下来
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Satellites stay in orbit because they move forward so fast that Earth’s gravity pulls them into a curved path instead of straight down.
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This balance between forward velocity and gravitational pull creates continuous free-fall around the planet.
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Low Earth orbit satellites travel about 17,500 miles per hour to maintain stable circular paths.
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If they moved slower, gravity would dominate and bring them down; if faster, they’d drift away into space.
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Orbital height matters too—higher orbits require less speed but take longer to circle Earth.
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Engineers calculate precise launch angles and velocities using Newton’s laws and Einstein’s relativity corrections.
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Atmospheric drag is minimal above 120 miles, allowing satellites to orbit for years without propulsion.
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Solar radiation pressure and gravitational tugs from the Moon or Sun cause tiny orbital changes over time.
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Ground stations track positions and occasionally fire small thrusters to adjust orbits as needed.
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This delicate dance of motion and gravity lets satellites deliver GPS, weather data, and global communications reliably.