Atmospheric Density Reconstruction Using Satellite Orbit Tomography

Abstract

Improved thermospheric neutral density models are required to better predict LEO satellite orbits. This research describes a new method to estimate the density using a tomography-based approach, where the orbit states of satellites serve as the measurements. The variational equation for the semimajor axis due to perturbing drag acceleration is used to relate the change in osculating specific mechanical energy of the orbit to the integrated density over the orbit. Using several such measurements from a number of satellites, one can estimate the density scale factor (i.e. a correction to an assumed density model). The problem considered here uses measurements from 100 satellites and solves for the spatially resolved global density scale factor discretized over 324 grid elements spanning 300 to 500 km altitude. This ill-posed problem is solved using Tikhonov regularization, with the 3D gradient chosen as the regularization operator, resulting in a penalty on the spatial smoothness of the estimated density. Preliminary simulation results show that the true time-averaged density can be reconstructed to within approximately 10%, using only simulated ground-based tracking measurements separated over 5 orbital revolutions.

Localized In-Situ Density Measurement in Low Earth Orbit via Drag Torque Estimation

“…Radar (or optical) tracking of passive bodies can reconstruct an atmospheric density model well, even if the bandwidth or resolution of the measurements is unable to capture small variations in the density. It has been shown by Shoemaker et al [14] that tomographic methods can be used to reconstruct density features beyond the resolution of any one measurement by considering different measurements as slices. By measuring the effect on many different satellites as they pass through a given region with different orbital properties, it is possible to reconstruct a fine density map of the region.…”

IMPACT: Integrated Modeling of Perturbations in Atmospheres for Conjunction Tracking

“…Here, rather than using the decay in x-ray intensity, we use the decay in orbital specific mechanical energy (j ). Shoemaker et al [32] describe the mathematical formulation and give simulation results [33] of an operationally realistic scenario. The method is outlined as follows:…”

A Framework for Integrated Modeling of Perturbations in Atmospheres for Conjunction Tracking (IMPACT)

“…Here, rather than using the decay in X-ray intensity, we use the decay in orbital specific mechanical energy (ξ). Shoemaker et al [32] describes the mathematical formulation, and Shoemaker et al [33] gives simulation results of an operationally realistic scenario. The method is outlined as follows:…”