Mercury-Atlas 4 (MA-4) was an uncrewed test flight within NASA's Project Mercury program, launched on September 13, 1961, at 14:04:16 UTC from Cape Canaveral Air Force Station Launch Complex 14. The mission's primary purpose was to evaluate the Mercury spacecraft's performance in orbit and to test the Mercury Space Flight Network. Despite initial technical challenges, Mercury-Atlas 4 successfully met its goals. The mission involved testing the Mercury spacecraft, specifically Mercury #8A, which completed one orbit around Earth. This successful flight provided important data and insights for NASA's Project Mercury, supporting the planning and development of upcoming crewed missions in the program.

Mercury-Atlas 5 was an American spaceflight of the Mercury program. It was launched on November 29, 1961, with Enos, a chimpanzee, aboard. The craft orbited the Earth twice and splashed down about 200 miles (320 km) south of Bermuda, and Enos became the first primate from the United States and the third great ape to orbit the Earth.