Manned earth entry at hyperbolic velocities.

Abstract

Problems that may occur during manned Earth entry in return from planetary missions are reviewed to evaluate the use of current technology and systems concepts in solution of such problems and to identify the advancements required. Analytical results show that a lift-todrag ratio (L/D) of 0.5 provides a sufficiently large entry corridor depth at velocities up to 55,000 fps to allow safe entry within the capability of existing guidance and navigation systems. An increase in vehicle slenderness to reduce radiant heating results in higher surface Reynolds numbers, thus increasing the possibility of boundary-layer transition and the attendant increase in convective heating. When radiation absorption and energy losses are included in the shock layer, the radiant heat transfer to blunt bodies is significantly less than that obtained in predictions which ignore these effects. Experimental data for the ablative heat shield of the Apollo command module imply that existing heat shields can provide efficient thermal protection for planetary return missions. Thus, for entry velocities up to 55,000 fps, the L/D's provided by blunt configurations appear sufficient for safe entry, and the associated heatshield weights are comparable to those of slender configurations.