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.

The Atlas LV-3B, Atlas D Mercury Launch Vehicle or Mercury-Atlas Launch Vehicle, was a human-rated expendable launch system used as part of the United States Project Mercury to send astronauts into low Earth orbit. Manufactured by Convair, it was derived from the SM-65D Atlas missile, and was a member of the Atlas family of rockets. With the Atlas having been originally designed as a weapon system, testing and design changes were made to the missile to make it a safe and reliable launch vehicle. After the changes were made and approved, the US launched the LV-3B nine times, four of which had crewed Mercury spacecraft.