Avoiding Earth Impacts Using Albedo Modification as Applied to 99942 Apophis

Current orbital solutions for 99942 Apophis predict a close approach to the Earth in April 2029. The parameters of that approach affect the future trajectory of Apophis, potentially leading to an impact in 2036, 2056, 2068, etc. The dynamic model used for this prediction does not account for non-gravitational perturbations including solar pressure and the Yarkovsky effect. Estimates of the displacement due to these perturbations range from -1500 to 1500km by 2029, comparable to 7? uncertainty in orbital solution. Uncertainties in physical characteristics stem from a lack of direct observations and a shortage of empirical data on similar objects. These perturbations, which stem from interactions with solar radiation, are directly related to the albedo of Apophis? surface. By modifying the average albedo of Apophis by 0.5%, between 4 and 15m of displacement can be effected between 2023 and 2029, rendering this method capable of avoiding all near-nominal solution keyholes. This modification is obtained by the deposition of electrostatically charged particles. These particles are charged via tribo-electrification and cure on the surface of Apophis creating a 30 micron thick layer of material with desired properties. This study found that a change in average albedo would nominally require 160kg of polytetrafluoroethylene (PTFE) to increase by 0.5% or 290kg of PTFE to decrease by 0.5%. The Apophis Exploration and Mitigation mission concept both improves accuracy of nongravitational perturbation models and delivers the albedo modification mechanism to Apophis, launching in 2021 and modifying albedo in 2023.