Conventional spacecraft structures were employed, following the proven materials and concepts demonstrated in the Mercury and Gemini designs. Primary structure consisted of a semimonocoque shell with reinforcements around cut-outs and fittings to distribute localized loads. Titanium was used as the basic shell material. Re-entry heat protection was conservatively designed for a controlled 17,000 km range, polar re-entry. The ablative material was M.A.C. Thermorad Shield S-3 elastomeric composite, which was being used for the Gemini blunt face heat shield. A 1.15 factor was applied to the predicted heating rates. Nominal material physical properties were used, determined from Project Gemini testing. Total ablative material design weight was 259 kg.