The Key To High-Precision GPS Satellite Orbits

A fundamental component of the Global Positioning System is the calculation of a highly accurate predicted orbit for each of the constellation spacecraft on a regular basis. In general, the parameters used to describe these orbits are not stable and need to be constantly updated. Being able to predict changes, and also being able to calculate the orbit after the fact, relies upon a combination of range observations and force modeling. A whole range of different forces, with varying magnitudes, act on the GPS satellites. Table 1 lists these forces in decreasing order of magnitude along with crude estimates of the accelerations they cause. There are also many smaller forces, such as drag effects, that are too small to worry about for current techniques. While the modeling of gravitational forces is well understood, the following forces Modeling Photon Pressure The Key To High-Precision GPS Satellite Orbits