Humans once traveled at nearly 40,000 kilometers per hour
During their return to Earth in May 1969, the crew of Apollo 10 reached a top speed of 39,897 kilometers per hour relative to Earth. This remains the official Guinness World Record for the highest speed ever attained by a crewed vehicle. Traveling at nearly 11 kilometers per second, the astronauts crossed from deep space into Earth's atmosphere in mere minutes.
The Dress Rehearsal for History
In May 1969, NASA launched Apollo 10, a mission designed as the definitive dress rehearsal for the first crewed lunar landing. Crewed by Commander Thomas Stafford, Command Module Pilot John Young, and Lunar Module Pilot Eugene Cernan, the mission was tasked with testing every procedure, maneuver, and hardware system of a lunar landing mission without actually touching down on the lunar surface. It served as the crucial bridge between Apollo 9, which tested the lunar module in low Earth orbit, and Apollo 11, which was scheduled to attempt humanity's first lunar landing two months later.
Apollo 10 followed an identical flight profile to the intended landing mission up to the final descent. The crew rode a Saturn V rocket out of Kennedy Space Center, conducted the translunar injection burn, and traveled approximately a quarter of a million miles to enter orbit around the Moon. Every milestone was tracked closely, as the mission's primary objective was to validate the operational procedures and lunar orbit navigation that Neil Armstrong and Buzz Aldrin would depend upon shortly thereafter.
Operations in Lunar Orbit
Once in lunar orbit, Stafford and Cernan boarded the Lunar Module, which had been given the callsign 'Snoopy', while Young remained in the Command and Service Module, designated 'Charlie Brown'. The two spacecraft undocked, and Snoopy performed a descent orbit insertion burn that brought the vehicle down to within approximately 8.4 nautical miles, or about 15.6 kilometers, of the lunar surface. This was the closest humans had ever been to another celestial body at that time.
At this low altitude, the crew tested the landing radar, photographed potential landing sites in the Sea of Tranquility, and evaluated the spacecraft's guidance systems. Although the Lunar Module was fully capable of flight in the lunar environment, its ascent stage was intentionally short of the fuel and equipment required to make a safe landing and subsequent ascent from the surface. After testing the staging mechanism and navigating through a brief automated control gyration during the staging process, Snoopy's ascent stage rendezvoused and docked successfully with Charlie Brown.