High Quality Content by WIKIPEDIA articles! In astrodynamics, the specific relative angular momentum of an orbiting body with respect to a central body is the relative angular momentum of the first body per unit mass. Specific relative angular momentum plays a pivotal role in definition of orbit equations. In an elliptical orbit, the specific relative angular momentum is twice the area per unit time swept out by a chord from the central mass to the orbiting body: this area is referred to by Kepler's second law of planetary motion.