The speed of a satellite, spacecraft, or other body travelling in an orbit around the earth or around some other celestial body. If the orbit is elliptical, the orbital speed, v, is given by:
where g is the acceleration of free fall, R is the radius of the orbited body, a is the semimajor axis of the orbit, and r is the distance between the orbiting body and the centre of mass of the system. If the orbit is circular, r=a and v=√(gR2/r).