Newton used his gravitational theory to explain the orbital motion of the planets and even foresaw the possibility of artificial satellites. Newton developed calculus to solve the problem of planetary motion, showing that the orbits of planets must be ellipses. The special case of circular orbits doesn’t require calculus and yields insights into orbital energy and spacecraft maneuvers. Consideration of gravitational energy also shows that it takes a finite speed—the so-called escape speed—for an object to break its bond with Earth or any other gravitating body.