Uncertainty propagation in the N-body problem using Dromo elements

Reliable and efficient uncertainty propagation is crucial for the task of monitoring possible impacts of Near Earth Asteroids with our planet. It is well known that a switch of the primary body can greatly reduce the numerical truncation error in the case of planetary flybys. In the present work, the advantages of performing a primary body switch in the uncertainty propagation problem are explored. For this purpose, first we present the linear uncertainty propagation using Dromo formulation, which has been shown in previous works to have a satisfactory performance when propagating the orbit uncertainty of Near Earth Asteroids. Next, we introduce the concept of primary body switch for the uncertainty propagation problem. The algorithm is based on the following procedure. We sample the initial orbit uncertainty distribution and linearly propagate the samples, considering the N-body gravitational influence. A primary body switch, which is a nonlinear mapping, is performed for all the samples at a threshold distance from the approaching planet, the Earth. The orbit of the samples is then linearly propagated with respect to the Earth using the Dromo formulation until the threshold distance is reached again. Finally, the propagation center is changed back to the heliocentric frame and the linear propagation continues. We apply the proposed method to an extensive set of asteroids that approach the Earth. Results suggest that the average error of the linear propagation can be reduced up to a factor of 30 when compared to a purely heliocentric linear propagation using Dromo elements.