Apollo 4

Apollo 4 was the first uncrewed test flight of the Saturn V launch vehicle, the rocket that would eventually carry astronauts to the Moon. Launched on November 9, 1967, from Kennedy Space Center's Launch Complex 39A, Apollo 4 (also designated AS-501) was an "all-up" test, meaning all three stages of the Saturn V were live and operational. The mission aimed to demonstrate the structural and thermal integrity of the Apollo spacecraft and the Saturn V, as well as the performance of the launch vehicle's propulsion, guidance, and control systems.

Apollo 4 successfully achieved its primary objectives. The Saturn V placed the Apollo Command and Service Modules (CSM) into a highly elliptical orbit. After two orbits, the S-IVB third stage reignited to simulate a translunar injection burn, sending the CSM into a high apogee of approximately 17,200 kilometers (10,700 miles). This allowed for a high-speed reentry test of the Apollo command module. The heat shield endured temperatures close to those expected during a lunar return. The mission lasted approximately 8 hours and 37 minutes.

Data gathered from Apollo 4 was crucial in validating the design and performance of the Saturn V rocket and the Apollo spacecraft, paving the way for future crewed Apollo missions. The success of Apollo 4 significantly reduced the risk associated with putting humans on the next Saturn V flight, Apollo 8.