Originally Posted by Peter47
There were two unmanned Saturn V launches before it lifted men into space. The first (Apollo 4 I believe) was successful, the second (Apollo 6) has serious problem with rocket oscillations - the pogo effect - and it was lucky that no one was on board. These were fixed before men were put on the top of the rocket.
Actually the pogo problem was only reduced, not fixed. On Apollo 13, the 2nd stage had such severe pogo vibration the entire launch vehicle almost broke up. The five engines experienced 68 g fore/aft vibration at 16 Hz, flexing the steel I-beam thrust structure by three inches. The vibration apparently tricked the center engine into fuel cutoff, which accidentally saved the vehicle.
13 Things That Saved Apollo 13, Part 5: Unexplained Shutdown of the Saturn V Center Engine
On the new Virgin Galactic engine, I wonder if it was tested in altitude chamber, or simply at ground level? If it was never tested in an altitude chamber, then this past manned mission was essentially the first realistic test.