A Simple Method for Correcting Empirical Model Densities during
Geomagnetic Storms Using Satellite Orbit Data
Abstract
Empirical models of the thermospheric neutral density are routinely used
by mission planners and systems engineers to perform orbit maintenance,
collision avoidance, and estimate time and location of re-entry for
spacecraft. These models have characteristic errors in neutral density
below 10% during geomagnetic quiet time, but perform worse during
intense geomagnetic activity, being unable to reproduce the significant
increases in the neutral density that are observed during geomagnetic
storms. Underestimation of the density during these conditions
translates to errors in orbit propagation that reduce the accuracy of
any resulting orbit predictions. These drawbacks directly translate into
safety risks for astronauts and orbiting spacecraft, but also limit our
understanding of the physics of neutral density enhancements. Numerous
CubeSats with publicly available ephemeris in the form of two-line
element (TLEs) sets orbit in this region. We present the Multifaceted
Optimization Algorithm (MOA), a method to estimate the neutral density
by minimizing the error between a modeled trajectory and a set of TLEs.
Specifically, the algorithm estimates corrections to the inputs of the
NRLMSISE-00 empirical density model, and applies those corrections
along-track the SWARM spacecraft orbits. This results in orbit-averaged
empirical densities below 10% error in magnitude, compared to errors in
excess of 25\% for uncalibrated NLRMSISE-00.