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

Abstract

[1] 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.Citation: Picone, J. M., J. T. Emmert, and J. L. Lean (2005), Thermospheric densities derived from spacecraft orbits: Accurate processing of two-line element sets,

Thermospheric Density and Wind Determination from Satellite Dynamics

“…Picone et al [2005] provides an algorithm, suitable for automated analysis on modern computers, that is more general and more powerful. It has been extensively applied in thermosphere research in recent years, and will be described in detail in Section 4.1.…”

“…A corotation and wind correction factor F was introduced by King-Hele [1987, section 2.5] and used by Picone et al [2005], so that…”

“…The analysis was performed for both the Russian GOST model [Cefola et al, 2003] and the American NRLMSISE-00 model [Yurasov et al, 2005b]. Trajectory information for the calibration objects was taken from publicly available TLE data, although the efficient densityderivation algorithm by Picone et al [2005], discussed in Chapter 4, was not yet available to the researchers. Instead, the TLEs were processed into trajectories, which were used to estimate ballistic coefficients, containing information on the density model error.…”

Ballistic Coefficient Estimation for Reentry Prediction of Rocket Bodies in Eccentric Orbits Based on TLE Data

“…This improves the estimation because the osculating data includes short-periodic variations whereas the mean TLE data does not [30].…”

“…The BC is estimated by comparing the change in semimajor axis according to two TLEs to the change in semimajor axis due to drag computed by accurate orbit propagation using an initial state derived from the first TLE (if not stated otherwise, states are obtained from TLEs using SGP4 to convert the TLE to an osculating state at the desired epoch and subsequently converting the state from the TEME to J2000 reference frame). Since short-periodic changes are removed from TLE data, the change in semimajor axis according to TLEs can be assumed to be purely the secular change caused by atmospheric drag (long-periodic variation of semimajor axis due to gravitational terms and SRP may be included in TLE data but are generally small compared to changes due to drag [30]). Therefore, any difference between the change in semimajor axis according to TLE data and due to drag computed by orbit propagation can be assumed to be caused by a wrong guess for the BC.…”