Gemini 4, piloted by Air Force Maj. James A. McDivitt, was part of a series of space flights in the mid-1960's. The Gemini capsule was a scaled-up version of the bell-shaped, blunt-ended Mercury capsule. It had 50 percent more cabin space and weighed more than twice as much. The Mercury program had shown that an astronaut could fly in orbit for up to 34 hours. NASA next had to determine whether crew members could endure the weightlessness of orbital free fall long enough to survive a journey to the moon and back. McDonnell Aircraft Corporation had the principal contract to produce the Gemini craft. Within five years, the program had achieved all of its objectives.