Overview of technical challenges of re-entry analysis of radioisotope heat sources

Abstract

The analytical and experimental effort conducted by the Applied Physics Laboratory of the Johns Hopkins University for the U.S. Department of Energy in predicting the re-entry ablation and thermostructural response of heat sources is described. The environment addressed is that posed by accidental entries of heat sources from an earth-gravity-assist trajectory, such as that of the Galileo mission. Also described are the analytical tools and limitations of the analytical methods used for thermal and thermostructural analysis and of the experimental databases used for material thermal and mechanical properties hi the analyses for these environments. These limitations are translated into challenges for improving re-entry predictions, for testing materials at very high temperatures, and for ablation tests at very high heating rates and pressures. Safety assessment for a mission is not addressed here.