Heat shielding for Venus entry probes.

Two contrasted approaches to ablative thermal protection of Venus entry probes are presented - a typical carbonaceous charring ablator and a dielectric reflective ablator. The interesting observation in this study is that mass loss is not the controlling variable in heat-shield sizing. A heat-soak problem determines the carbon phenolic sizing. For Teflon, the material thickness required to accomplish reflection is the sizing factor. The total heat-shield weight required to handle either steep or shallow entry is computed to be 13% less for a Teflon shield (if at least 3.2 mm are required for reflection) than for a charring ablator shield. If an efficient reflective backing is used with Teflon, the thickness can be reduced 1.0 mm and the computed weight is 31% less for Teflon than for the charring ablator. Such weight reductions may significantly increase the science payload weight of the miniprobes.