Drag coefficient is a major source of uncertainty in calculating the aerodynamic forces on satellites in low Earth orbit. Closed-form solutions are available for simple geometries under the assumption of free molecular flow; however, most satellites have complex geometries, and a more sophisticated method of calculating the drag coefficient is needed. This work builds toward modeling physical drag coefficients using the direct simulation Monte Carlo method capable of accurately modeling flow shadowing and concave geometries. The direct simulation threedimensional visual program and the direct simulation Monte Carlo analysis code are used to compare the effects of two separate gas-surface interaction models: diffuse reflection with incomplete accommodation and quasi-specular Cercignani-Lampis-Lord models. Results show that the two gas-surface interaction models compare well at altitudes below ∼500 km during solar maximum conditions and below ∼400 km during solar minimum conditions. The difference in drag coefficient of a sphere at ∼800 kmcalculated using the two gas-surface interaction models is ∼6% during solar maximum and increases to ∼10% during solar minimum. The difference in drag coefficient of the GRACE satellite computed using the two gas-surface interaction models at ∼500 km differs by ∼15% during solar minimum conditions and by ∼2-3% during solar maximum conditions.
Bibliographical noteFunding Information:
Funding for this work was provided by the U.S. Department of Energy through the Los Alamos National Laboratory/Laboratory Directed Research and Development program as part of the Integrated Modeling of Perturbations in Atmospheres for Conjunction Tracking project. Part of the funding was provided by the U.S. Department of Defense Experimental Program to Stimulate Competitive Research grant FA9550-10-1-0038 administered by the U.S. Air Force Office of Scientific Research. The authors would like to thank Eric Sutton for providing the drag coefficient data for GRACE. The authors would also like to thank Vivek Ram, graduate student at the University of Kansas, for his help with developing the high-fidelity GRACE CAD model.