Abstract
Atmospheric drag describes the main perturbing force of the atmosphere
on the orbital trajectories of near-Earth orbiting satellites. The
ability to accurately model atmospheric drag is critical for precise
satellite orbit determination and collision avoidance. Assuming we know
atmospheric winds and satellite velocity, area and mass, the primary
sources of uncertainty in atmospheric drag include mass density of the
space environment and the spacecraft drag coefficient, CD. Historically,
much of the focus has been on physically or empirically estimating mass
density, while CD is treated as a fitting parameter or fixed value.
Presently, CD can be physically modeled through energy and momentum
exchange processes between the atmospheric gas particles and the
satellite surface. However, physical CD models rely on assumptions
regarding the scattering and adsorption of atmospheric particles, and
these responses are driven by atmospheric composition and temperature.
Modifications to these assumptions can cause CD to change by up to
~40%. The nature and magnitude of these changes also
depend on the shape of the spacecraft. We can check the consistency of
the CD model assumptions by comparing densities derived from satellite
drag measurements and computed CD values for satellites of different
shapes orbiting in the same space environment. Since all of the
satellites should see the same density, offsets in the derived densities
should be attributable to inconsistencies in the CD model. Adjusting the
CD model scattering assumptions can improve derived density consistency
among the different satellites and inform the physics behind CD
modeling. In turn, these efforts will help to reduce uncertainty in CD,
leading to improved atmospheric drag estimates.