Thermospheric densities derived from spacecraft orbits: Accurate processing of two‐line element sets

This paper presents a new, fast, and accurate method for retrieving the total mass density of the upper atmosphere from routinely compiled trajectories of objects in low Earth orbit. Comparison to density values from state‐of‐the‐art precision orbit determination calculations on routine tracking observations shows our results to be of comparable accuracy at vastly lower computational and administrative costs, a result both unprecedented and unforeseen. This means that the difficulty of obtaining raw observational data and precision orbit determination software is no longer an obstacle to the scientific analysis of orbits. The accessibility of orbital elements and the speed and accuracy of the new method enable the use of a vast and growing archive of global data for analysis of thermospheric evolution and responses to solar, and possibly geomagnetic, forcing. The new procedure defines precisely the effective density values that may be extracted from orbit data; these values are explicitly independent of any atmospheric model. The discussion also contrasts the new approach with past analytic methods and with standard precision orbit techniques.