orbit Once phasing orbit period is determined, the phasing orbit semimajor axis can be derived from the period formula: where a2 is defined as semimajor axis of phasing orbit T2 is defined as period of phasing orbit μ is defined as Standard gravitational parameter From the semimajor axis, the phase orbit apogee and perigee can be calculated: where a2 is defined as semimajor axis of phasing orbit ra is defined as apogee of phasing orbit rp is defined as perigee of phasing orbit Finally, the phasing orbit's angular momentum can be found from the equation: where h2 is defined as angular momentum of phasing orbit ra is defined as apogee of phasing orbit rp is defined as perigee of phasing orbit μ is defined as Standard gravitational parameter To find the impulse required to change the spacecraft from its original orbit to the phasing orbit, the change of spacecraft velocity,∆V, at POI must be calculated from the angular momentum formula: where ∆V is change in velocity between phasing and original orbits at POI v1 is defined as the spacecraft velocity at POI in original orbit v2 is defined as the spacecraft velocity at POI in phasing orbit r is defined as radius of spacecraft from the orbit’s focal point to POI h1 is defined as angular momentum of original orbit h2 is defined as angular momentum of phasing orbit Remember that this change in velocity, ∆V, is only the amount required to change the spacecraft from its original orbit to the phasing orbit. A second change in velocity equal to the magnitude but opposite in direction of the first must be done after the spacecraft travels one phase orbit period to return the spacecraft from the phasing orbit to the original orbit. Total change of velocity required for the phasing maneuver is equal to two times ∆V. Orbit phasing can also be referenced as co-orbital rendezvous like a successful approach to a space station in a docking maneuver. Here, two spacecraft on the same orbit but at different true anomalies rendezvous by either one or both of the spacecraft entering phasing orbits which cause them to return to their original orbit at the same true anomaly at the same time. Phasing maneuvers are also commonly employed by geosynchronous satellites, either to conduct station-keeping maneuvers to maintain their orbit above a specific longitude, or to change longitude altogether. See also Orbital