Apollo 6, launched in April 1968, was the Apollo programme's second and last unmanned test flight of its Saturn V launch vehicle.
Unlike the near perfect flight of Apollo 4, Apollo 6 experienced problems right from the start. Two minutes into the flight, the rocket experienced severe oscillations for about 30 seconds.
In part due to the vibrations, the spacecraft adaptor that attached the CSM and mockup of the Lunar Module to the rocket started to have some structural problems. Airborne cameras recorded several pieces falling off.
After the first stage was jettisoned at the end of its task, the S-II second stage began to experience its own problems. Engine Number Two (of five) had performance problems from 206 to 319 seconds after liftoff and then at 412 seconds shut down altogether. Two seconds later Engine Number Three shut down as well. The onboard computer was able to compensate and the stage burned for 58 seconds more than normal.
Due to the less than nominal launch, the CSM and S-IVB were now in a 178 by 367 km orbit instead of the planned 160 km circular orbit. But after two orbits of checking out the spacecraft and rocket stage the S-IVB failed to restart to simulate the Trans Lunar Injection burn that would send the astronauts to the Moon.
It was decided to use the Service Module engine to raise the spacecraft into a high orbit in order to complete some of the mission objectives. It burned for 442 seconds, longer than it would ever have to on a real Apollo mission and raised the apogee of the orbit to 22,200 km. There was now however not enough fuel to speed up the reentry and the spacecraft entered the atmosphere at a speed of 10 000 m/s instead of the planned 11 270 m/s. This meant it landed 80 km from the planned touch down point.
Music: Marcus P. Graf