How Fast Is 'Orbit'?
🛰️ Orbital mechanics
Question
How fast do you have to go to orbit the Earth?
One equation gives the speed of every circular orbit: v = √(GM/r). Go low, go fast; go high, go slow. The ISS needs 7.66 km/s - about 20 times the speed of a rifle bullet. The Moon, 385,000 km out, cruises at just 1.02 km/s. GPS satellites at 20,200 km go 3.9 km/s. And if you ever want to leave Earth's gravity for good, you need √2 times the orbital speed: 11.2 km/s, the escape velocity.
The math
v = √(GM/r) with GM = 3.986×10¹⁴ m³/s². ISS (r = 6,791 km): 7,661 m/s. Moon (r = 384,400 km): 1,018 m/s. GPS (r = 26,551 km): 3,875 m/s. Escape velocity at the surface: √(2GM/R) = 11,187 m/s.
Why it matters
This single equation predicts the speed of every orbiting object you can see - plug in the distance and check it against reality. Try it: 400 km → 7.7 km/s. It works, every time, for everyone's satellites.
Linked from
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