Smart guidance

With much of the atmosphere behind it and the second stage working smoothly, the

Saturn changed the way it guided itself to orbit. So far. it had not compensated for any distance that the wind and other forces had pushed it from its ideal flight path. Nor had it tried to correct for any under – or over-performance of the engines. Instead, during the tilt sequence, the instrument unit had merely kept track of where it was at any moment. The new guidance regime was given a typically NASA-cse name of the iterative guidance mode. While in force, equations in the Saturn’s computer plotted the most efficient flight path from ‘wherever the vehicle was’ to The point in space where it wanted to go’ – in this case, insertion into a parking orbit around Earth. To anthropomorphise the situation, what the computer was thinking was, “OK, 1 know where the wind and such has pushed me to. What must 1 do to reach the position and speed that I have to reach?” As the S-II powered ahead, the computer monitored the vehicle’s progress and sent steering commands to the four gimballed outer engines as necessary to achieve the desired result. This steering was maintained for the rest of the S-II burn. It was then suspended and the stack’s attitude held steady until the S-II had dropped away and the third stage had ignited to pow’er the vehicle to orbit. With the S-IVB thrust established, the steering recommenced.