The concepts of radiation cooling and ablation cooling using char-forming plastic materials are examined for the purpose of providing thermal protection for ballistic vehicles entering the earth's atmosphere from near earth orbits. The effect on thermal protection requirements of re-entry from various orbit altitudes is presented. A general theory for charring ablation materials is discussed. Rapid means for calculation of aerodynamic heating encountered during ballistic re-entry are furnished. Design charts based on these data are included for determination of thermal protection weights when using ablation or radiation cooling. Weights are based on maintaining a controlled environment for the vehicle's interior and loadcarrying structure.