The Mercury spacecraft's principal designer was Maxime Faget, who started research for human spaceflight during the time of the NACA. It was long and wide; with the launch escape system added, the overall length was . With of habitable volume, the capsule was just large enough for a single crew member. Inside were 120 controls: 55 electrical switches, 30 fuses and 35 mechanical levers. The heaviest spacecraft, Mercury-Atlas 9, weighed fully loaded. Its outer skin was made of René 41, a nickel alloy able to withstand high temperatures.