The P1 approximation of the spherical harmonics method is applied for the radiative heating calculation of space vehicles entering Mars's atmosphere. Surface radiative heating of a spherical space vehicle and a Pathfinder-shape space vehicle in a viscous, heat conductive, and chemically nonequilibrium gas mixture is studied. Unstructured grids are used to integrate the radiation heat transfer equation. The multigroup spectral model is applied to describe the optical properties of absorbing and emitting media. The chemical model includes 10 species and 79 reactions. Two physically and chemically nonequilibrium points of trajectory are studied. Satisfactory agreement has been obtained between the P 1 approximation and the ray-tracing method. Two algorithms have also been proposed to avoid physical inaccuracy of the P 1 approximation in optically thin gas. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.