In September 1967, in the wake of the Apollo 1 tragedy, NASA’s Manned Space Flight Administrator George Mueller approved a set of benchmarks that would lead up to a manned mission to the moon and beyond. The benchmarks were designed to ensure that each element of the rocket, Lunar Module (LM), and the Command/Service Module (CSM) were tested to ensure the safety of the Apollo crews.
As each stage would need to be completed successfully before moving onto the next, Mueller opted to designate each benchmark with a letter that could accompany an Apollo mission number. The first two benchmarks (A and B) were unmanned missions that would be used to validate the Saturn V launch vehicle and the LM. C would be a manned mission to validate the CSM in orbit around the Earth. D and E would be manned missions aiming for increasingly higher orbits of Earth. The F mission would essentially be a dress rehearsal for the moon landing completing every stage apart from the actual landing. Finally, G would see two astronauts land on the surface of the moon. The planned benchmarks extended past the first moon landing with additional lunar landings, an orbital survey mission, and extended stays on the lunar surface proposed.
The first Apollo mission was designated Apollo 4 with Mueller choosing to retire the Apollo 1 designation to honour the crew that tragically perished. Mueller took the three unmanned missions (AS-201, AS-202, and AS-203) into account to arrive at the Apollo 4 designation. The first Apollo mission was launched on November 9, 1967, carrying an unmanned Block 1 CSM. After completing 3 orbits, the CM completed a successful retry with engineers using the Service Module’s engine to ram the CM into the Earth’s atmosphere to test the heat shield at higher than normal Earth-orbital reentry speeds. The extreme reentry was conducted to test the heat shield’s ability to withstand a trans-lunar reentry.
Apollo 5 and 6 were both uncrewed missions that successfully completed the A and B benchmarks. The crewed C benchmark was achieved successfully with the launch of Apollo 7 on October 11, 1968. Wally Schirra, Walt Cunningham, and Donn Eisele spent 11 days in the CSM orbiting Earth.
Although the next benchmark, D called for an Earth orbit mission, on September 15, 1968, the Soviet Union sent a range of lifeforms including two tortoises around the moon. Seeing an opportunity to overtake the Soviets, Apollo Spacecraft Program Office (ASPO) manager, George Low suggested that they skip the D benchmark and attempt a lunar return mission. The Apollo 8 crew (Frank Borman and Jim Lovell, and rookie William Anders) launched from Pad 39a at the Kennedy Space Center on December 21, 1968. Over the 6-day mission, the crew of Apollo 8 would capture the attention of the world completing 10 lunar orbits over Christmas Eve.
In contrast, the Apollo 9 mission was a relatively dull affair. The mission was used to test rendezvous and docking procedures and the use of the EVA suit outside the LM. It essentially covered the D and E benchmarks.
Apollo 10 was a dress rehearsal for the mission that would eventually see man’s first steps on the lunar surface. Gemini veterans Thomas P. Stafford, John Young and Eugene Cerna launched on May 18, 1969. After achieving lunar orbital insertion, Stafford and Cerna boarded the LM and descended to within just 15 kilometers (50,000 feet) of the surface of the moon. In what must have taken a titanic amount of self-control to not actual touchdown after coming so close, the pair returned to the CSM departing lunar orbit on May 24. The three-man crew splashed down in the Pacific Ocean at 16:52 on May 26 and were retrieved by the USS Princeton.
Just over a decade after Alan Shepard became the first American in space, the United States stood at the precipice of one of the greatest achievements in human history.