Orbital speed

The maximum (instantaneous) orbital speed occurs at periapsis (perigee, perihelion, etc.

), while the minimum speed for objects in closed orbits occurs at apoapsis (apogee, aphelion, etc.).

In ideal two-body systems, objects in open orbits continue to slow down forever as their distance to the barycenter increases.

The sign of the result may be positive, zero, or negative and the sign tells us something about the type of orbit:[1] The transverse orbital speed is inversely proportional to the distance to the central body because of the law of conservation of angular momentum, or equivalently, Kepler's second law.

This is an approximation that only holds true when the orbiting body is of considerably lesser mass than the central one, and eccentricity is close to zero.

[7] Objects passing Earth's orbit going faster than 42.1 km/s have achieved escape velocity and will be ejected from the Solar System if not slowed down by a gravitational interaction with a planet.