Trouble began on the sixth day of the flight, November 17. The capsule developed an atmospheric leak, the pressure first dropping from 760 to 380 mm of Mercury. With the drop in cabin pressure all the animal test subjects died. It would have killed any Cosmonaut not wearing a spacesuit.
The first attempt for a Zond 4 follow-up launched on April 22. It failed when the Launch Escape System sent an erroneous abort command at T+260 seconds and shut down the Proton booster’s second stage. The escape rocket fired and pulled the descent module to safety.
The success of Apollo 4 gave good reason to believe that the Saturn V could be trusted to propel men into space. But NASA pushed on with its plans for a second unmanned booster flight, primarily to give the Pad 39 launch team another rehearsal before sending men into deep space on the Saturn V. The mission was called Apollo 6…
Apollo Saturn 201 employed the Saturn IB launch vehicle, which was the up-rated version of the Saturn I rocket flown in ten earlier Saturn-Apollo missions. It featured an upgrade of the first stage engines to increase thrust from 1,500,000 lb-ft of thrust to 1,600,000 lb-ft. The second stage was the S-IVB. This stage used a new liquid hydrogen-burning J-2 engine which would also be used on the S-II second stage of the Saturn V lunar launch vehicle…
Max Faget’s position was that considering the difficulty of the job, if each mission was successful half the time, it would be well worth the effort. But Gilruth thought that was too low. He want a 90% mission success ratio and a 99% ratio for Astronaut safety. Walt Williams who was currently running the Mercury program believed that astronaut safety needed to be limited to only 1 failure in a million which was 99.9999%.
…From the information they gathered on the existing technical problems, Disher and Tischler concluded that prospects were only one in ten that Apollo would land on the moon before the end of the decade….
“The contractor role in Houston was not very firm. Frankly, they didn’t want us. There were two things against us down there. Number one, it was a Headquarters contract, and it was decreed that the Space Centers shall use GE for certain things; and number two they considered us (meaning GE) to be Headquarters spies.” Edward S. Miller of General Electric.
The Apollo contract specified a shirt-sleeve environment. For this reason, North American was told not to include in its design a hatch that opened by explosives, like Mercury’s. An accidentally blown hatch in space would cause an instant vacuum and certain death for an astronaunt not wearing his pressure suit.