Minimum-mass design of sandwich aerobrakes for a lunar transfer vehicle

Abstract

A structural mass optimization study of a sandwich aerobrake for a lunar transfer vehicle was conducted. The proposed spherical aerobrake had a base diameter of 15.2 m and radius of 13.6 m. A hot thermal protection system (TPS) and cold structure were used in the design. Honeycomb sandwich aerobrake structures made up of four different materials—aluminum alloy, titanium alloy, graphite-epoxy, and graphite-polyimide—were considered. Cases of aerodynamic load, equivalent uniform pressure, and aerodynamic plus thermal load were analyzed. Both linear stress and buckling analyses were conducted for a range of skin and core thicknesses. A graphical optimization procedure was used to determine the skin and core thicknesses of a minimum-mass aerobrake. The design criteria used were material strength, global buckling, and TPS tile deformation. Among them, the TPS deformation criterion was the most critical. The graphite-epoxy aerobrake was the lightest among the four materials studied. Its total mass is about 12.3% of the LTV mass, for supports at 75% span. Equivalent uniform loading produced smaller deformations, stresses, and buckling loads than did the more realistic aerodynamic loading for the same aerobrake configuration. Thermally induced stresses countered the aerodynamically induced stresses and hence had a beneficial effect on the deformation and buckling of the aerobrake.