Radial velocity Radial velocity The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial velocity is the component of the object's velocity that points in the direction of the radius connecting the object and the point. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from or approaches the Earth. In astronomy, radial velocity is often measured to the first order of approximation by
Escape velocity cases, the spacecraft may be first placed in a parking orbit (e.g. a low Earth orbit at 160–2,000 km) and then accelerated to the escape velocity at that altitude, which will be slightly lower (about 11.0 km/s at a low Earth orbit of 200 km). The required additional change in speed, however, is far less because the spacecraft already has significant orbital velocity (in low Earth orbit speed is approximately 7.8 km/s, or 28,080 km/h). The escape velocity at a given height is formula_15 times the speed in a circular orbit at the same height, (compare this with the velocity