The Mean Motion Double Dot is defined as one sixth the second time derivative of the Mean Motion, measured in orbits per day per day per day (orbits/day3). It basically defines the rate of change of the Mean Motion Dot from day to day so that some orbit propagation software can continue to predict the location of the satellite accurately.
The mean motion double dot is normally zero unless the satellite is being maneuvered or is undergoing orbit decay.
The format of the Mean Double Dot is:
Sign: (nil or -): The sign of the digits succeeding it.
No sign indicates positive;
If a Mean Motion Dot Term was "-12345-6" within a TLE, it would mean -0.12345x10-6 orbits/day3 or in scientific notation:
Not all orbit propagators read or use this value.
Mean Motion Double Dot Was Last Modified On May 23, 2010