Variable node drag parameterization for reentry trajectory estimation

A numerical parameter optimization technique was used to determine the piecewise continuous polynomial approximation to the drag coefficient history that produces a reentry trajectory that best matches radar data in a weighted least squares sense. The drag coefficient was parameterized in terms of node point locations, and polynomial coefficients or function values at the nodes. Estimation of node locations for drag coefficient histories using simulated radar data reduced data residuals by almost one half through improved approximation of the sharp rise in drag coefficient caused by boundary layer transition.