How fast is a satellite?

A satellite is like a ship flying in space. Satellites do not stay in the same place, but continue to fly with speed. So, how fast do satellites fly?

Earth observation satellites fly in orbits at altitudes of about 200 to 2,000 km, called low earth orbit, at a speed of about 28,800 km per hour. This is about 90 times faster than the maximum speed of the Shinkansen bullet train, which is said to be 320 km per hour. This speed is necessary to avoid falling to the Earth due to the gravity.

In addition, satellites such as weather satellites and communications satellites flying in orbits, called geostationary orbit, always seem to be in the same place when you look up at the sky. In other words, the satellite is flying at the same speed as the Earth’s rotation. This speed can be calculated using the altitude of the orbit and the Earth radius.

The geostationary orbit is about 36,000 km above the equator, and the Earth radius is known to be about 6,400 km. Since the satellite is moving on the circumference of the circle of radius r centered on the Earth, the flight distance in one day can be calculated by the circumference formula “length of circumference = 2 x π (circular constant) x r”, as follows. r is 36,000 + 6,400 = 42,400.

2×π×r = 2 × 3.14 × 42400 （㎞）= 266,272　（km）
　　　　　　（Calculated assuming π=3.14）

The satellite circles this distance in one day (24 hours). The speed is calculated by “distance/time.”

266272（㎞） ÷ 24（hours） = 11,095　km/h

This speed is less than half the speed of Earth observation satellites, but by keeping this speed in geostationary orbit, the satellite always appears to be at a single point in view of the Earth. In this way, satellites fly at a speed determined by their respective purpose. In order to achieve the speed, it is needed to accelerate satellites with a rocket and others.