BACK IN THE SADDLE: APOLLO 4

NASA resumed Apollo operations on 9 November 1967 with Apollo 4. It was an А-mission to test the Saturn V launch vehicle. As so often happens with new, complex systems, getting this vehicle ready for flight proved to be a slow, difficult affair. Its S-II stage repeatedly exhibited cracks during in­spections, and the unmanned Block I spacecraft, CSM-017, tested modifica­tions called for by the investigation into the AS-204 fire.

The Saturn V launch vehicle turned the normal procedures of rocket devel­opment upside down. Traditionally, engineers undertook a careful, pro­gressive programme of testing a rocket stage to ensure that it worked before setting another stage on top, and testing that. To test the entire config­uration at once – so-called all-up testing – was deemed too risky. How­ever, when George Mueller became head of NASA’s Office of Manned Space Flight in 1963 he argued that the incremental approach to testing rocket stages not only wasted expensive

flight-capable stages, it also wasted precious time. He ordered that the engineering and ground testing of the rocket’s components should be of such a quality that all stages of the vehicle could be flight tested at the same time. Apollo 4 would prove to be a triumphant vindication of this strategy. The launch issued a noise like nothing that had ever been heard at the Kennedy Space Center, and this blew away much of the lingering pessimism from the spacecraft fire. As the acoustic and thermal energy was enough to cause substantial damage to the launch tower, NASA had subsequently to make modifications to the launch pads in order to suppress the extreme conditions.

As well as testing the entire rocket system, Apollo 4 placed its CSM payload into a high ballistic arc. From here, the SPS engine powered the command module into a high-speed dive into the atmosphere to test its heatshield by re-entering at the speed it would have if it were returning from the Moon. The CM was recovered from the Pacific Ocean after an 8 /4-hour flight that, in all important respects, was a complete success.