Why is Period needed for Kepler inputs

[NASA_SimGuy]

Why is the orbital period needed for Kepler inputs? Our simulation determines the orbital speed around the moon as a function of radius from the moon. I comented out the period and the vehicle did not initialize properly. Is there a way to have Celestia's velocity use the radius from the moon?

EllipticalOrbit {
#Period 0.064176392
SemiMajorAxis 3999.90
Eccentricity 0.00005
Inclination 29.999
AscendingNode 343.1518
ArgOfPericenter 346.2476
MeanAnomaly 13.8216
Epoch 2451545.0
}

[selden]

Both SemiMajorAxis and Period are required by EllipticalOrbit and are the only parameters which are required. Celestia does not (currently?) contain any code to calculate the Period. However, you can specify your own orbital calculations if you replace EllipticalOrbit by ScriptedOrbit. See https://en.wikibooks.org/wiki/Celestia/Trajectories#ScriptedOrbit