Satellites orbit the Earth. But how do spacecraft break free of the Earth's gravitational pull? If its speed is fast enough, inertia overcomes gravity and the spacecraft can break free of orbit. This speed is known as escape velocity. It is the minimum speed needed to escape the gravitational field of a particular body. It has beer calculated that if an object is launched upward at 25,128 miles pe hour (6.98 miles per second) it will escape the gravitational force o Earth and never fall back. This speed, 25,128 miles per hour, is Earth' escape velocity.