Mercury-Atlas 3 (MA-3) was an unmanned spaceflight of the Mercury program. It was launched unmanned on April 25, 1961 at 16:15 UTC, from Launch Complex 14 at Cape Canaveral, Florida. The Mercury capsule contained a robotic "mechanical astronaut". Mercury spacecraft No. 8 and Atlas No. 8 100-D were used in the mission.

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.