meanAnomaly property
Mean Anomaly in Degrees. Now that we have the size, shape, and orientation of the orbit firmly established, the only thing left to do is specify where exactly the satellite is on this orbit ellipse at some particular time. Our very first orbital element (Epoch) specified a particular time, so all we need to do now is specify where, on the ellipse, our satellite was exactly at the Epoch time. Anomaly is yet another astronomer-word for angle.Mean anomaly is simply an angle that marches uniformly in time from 0 to 360 degrees during one revolution.It is defined to be 0 degrees at perigee, and therefore is 180 degrees at apogee. If you had a satellite in a circular orbit (therefore moving at constant speed) and you stood in the center of the earth and measured this angle from perigee, you would point directly at the satellite.Satellites in non-circular orbits move at a non-constant speed, so this simple relation doesn’t hold. This relation does hold for two important points on the orbit, however, no matter what the eccentricity.Perigee always occurs at MA = 0, and apogee always occurs at MA = 180 degrees. It has become common practice with radio amateur satellites to use Mean Anomaly to schedule satellite operations.Satellites commonly change modes or turn on or off at specific places in their orbits, specified by Mean Anomaly. Unfortunately, when used this way, it is common to specify MA in units of 256ths of a circle instead of degrees! Some tracking programs use the term “phase” when they display MA in these units. It is still specified in degrees, between 0 and 360, when entered as an orbital element. Example: Suppose Oscar-99 has a period of 12 hours, and is turned off from Phase 240 to 16. That means it’s off for 32 ticks of phase.There are 256 of these ticks in the entire 12 hour orbit, so it’s off for (32/256)x12hrs = 1.5 hours. Note that the off time is centered on perigee. Satellites in highly eccentric orbits are often turned off near perigee when they’re moving the fastest, and therefore difficult to use.
Implementation
final double meanAnomaly;