Orbit

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory.

To completely describe an orbit mathematically, six quantities must be calculated. These quantities are called orbital elements, or Keplerian elements. They are:

1. Semi-major axis length apoapsis to center of the ellipse.
2. Eccentricity, a measurement of the orbit’s ellipse (an eccentricity of zero indicates a circular orbit. Written as E
   1. Eccentricity = ((Major axis2)-(Minor axis2)/Major axis).
3. Inclination, the angular distance of the orbital plane from the plane of the planet’s equator: Written as I
4. Periapsis is the elevation closest to the planet: Written as AP
5. Apopsis is the elevation furthest from the planet surface: Written as AA
6. True Anomaly is an angular parameter that defines the position of a body moving along a Keplerian orbit

As a pilot you will be most concerned with the E and AP.
If you have a high E you are either risking flying of in to space or crashing in to the planet.
Obviously if you have a High E and AP is counting down to 0 you really need to start thinking about how not to crash in to the planet.
rana 15:16, 14 March 2007 (HKT)

Useful things pilots want to know

TVM - Get to Target in the shortest route.
DOR - Get in a prefect circular orbit using least fuel.