A heat shield protected the two-man Gemini spacecraft against the enormous heat of reentry into the atmosphere beginning at a velocity of more than 27,500 kilometers (17,000 miles) per hour. Like those of other early human spacecraft, Gemini's heat shield derived from ballistic-missile warhead technology. The dish-shaped shield created a shock wave in the atmosphere that held off most of the heat. The rest dissipated by ablation: charring and evaporation of the shield's surface. Ablative heat shields are not reusable.
The ablative substance of the Gemini heat shield is a paste-like silicone elastomer material which hardens after being poured into a honeycomb form. In 1970 McDonnell-Douglas gave this unused heat shield to the Smithsonian on behalf of NASA.
Transferred from the National Aeronautics and Space Administration through McDonnell Aircraft Corp.