The OrbitPeriapsis method is a conditional property that can be used with the Step command to advance the Spacecraft to periapsis, the point in the orbit where the Spacecraft is at its closest approach to a Planet, Moon, or CelestialObject. FreeFlyer determines this condition by monitoring the dot product between the position and velocity vectors and identifying when this value passes from negative to positive. The celestial body to be used in the periapsis calculation can be specified using a Variable, String, or CelestialObject. If a celestial body is not specified, the current Spacecraft Central Body will be used.
Note that as a general rule this method should only be used as a propagation stopping condition and should not be used as a means monitor whether or not a Spacecraft is at the periapsis of its orbit at a particular epoch.
Timing Precision Mode
This page describes functionality in nanosecond timing precision mode.