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USA 179


Tyneside, UK
2018 Jul 23
Monday, Day 204

Maintained by:






USA-179 Analysis:









Orbital Adjustments in the Second Half of 2006

During the first six months of detailed observation, plotted below, twoline frequent orbital element sets were available from a non-public source. They enabled verification of the calculation method for the Mean Motion, as can be seen from how well the radio-derived values match with them.

The pattern that arises is that the satellite orbits for about 20 days and then an adjustment is made. Gravitational, rather than atmospheric, influences cause the Mean Motion to increases with time. In turn, this causes the ground track to drift in an easterly direction from day to day and, as the value gets higher, the ground track movement accelerates. The purpose of the adjustments is to reverse the drift and keep the location of the ground track within operational bounds. The initial routine was a major adjustment followed by a minor one but, towards the end of the year, it had evolved into two minor adjustments for every major one.

There are probably frequent smaller 'tweaks' between the ones plotted here but they are too fine (with certain exceptions) to be seen in the plot.

The Mean Motion seems to be bounded by values of 2.00675 and 2.00552, equating to orbital periods of 717.58 and 718.02 minutes respectively.

USA 179 2006
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