Apollo 6

Apollo six was launched on April 4, 1968, and was the mission that was supposed to determine the final qualification of the Saturn V rocket, which included the testing of the Apollo Command center, Command Module, and Lunar Module. This mission copied the test procedure in Apollo's four and five, but the results from Apollo six did not end up successful like the test results from Apollo's four and five. Two minutes after the launch, structural parts in the Lunar Module were lost. Not too long after that, two of the five engines shut off before they were supposed to in the second stage of the boost phase. After the third stage of the rocket failed to ignite, the rocket re-entered the earth and was recovered in good condition. Even though the mission failed, it was useful because NASA had learned what had gone wrong and sought to correct the problem. In fact, they had gained so much out of Apollo 6, that they wanted to start manned Apollo missions.

Facts and Statistics from the NSSDC (National Space Science Data Center) Master Catalog:

Three major problems occurred during the mission. Two minutes and five seconds after launch, the Saturn V structure underwent a severe pogo oscillation, without damage to the spacecraft structure. Due to a manufacturing flaw and unrelated to the pogo oscillations, structural panels were lost from the lunar module adapter. Finally, after the completion of first stage firing and part way through the second stage burn, two of the five second stage J-2 engines shut down prematurely. The planned 175 km circular Earth orbit was not achieved, instead, after completion of the third stage burn, the spacecraft was in a 172.1 x 223.1 km, 89.8 min orbit. After two orbits, the third stage failed to reignite as planned, so the Service Module propulsion system was used to boost the spacecraft to an apogee of 22,225.4 km, from which the planned lunar reentry simulation took place at 36,025 km/hr, slightly less than the planned velocity of 40,000 km/hr. The Command Module splashed down 80 km off target 9 hr 50 min after launch and was recovered in good condition.