noun
orbital speed
Technical term in astronomy for the speed at which a celestial body moves along its orbit.
地球の公転速度は約30km/sです。
The Earth's orbital speed is about 30 km/s.
自転速度 refers to rotational speed (spinning on an axis), while 公転速度 refers to orbital speed (revolution around another body).
Compound of 公転 (revolution, orbit) and 速度 (speed).