ASC-15 For Saturn I
No guidance computer was used for Saturn I Block I (missions SA-1, 2, 3 and 4). The guidance system for SA-2 is shown in Figure 4. The pitch program was provided by a cam device located in the Servo Loop Amplifier Box. The sequence of events was controlled by a program device that was also used on Jupiter missiles. This was a 6-track tape recorder that sent pulses to a set of relays (the flight sequencer) to activate and deactivate various circuits in a precisely timed sequence.
The ASC-15 was first flown on SA-5, the first Saturn I Block II vehicle and the first to achieve orbit. It was a passenger on this mission, not guiding the vehicle but generating test data for later evaluation. The active guidance system on SA-5 was similar to that of earlier flights. The passenger system was the ASC-15 and the ST-124 inertial platform. Guidance was open loop; that is guidance commands were functions only of time. SA-5 also saw the introduction of the Instrument Unit.
On SA-6, while open loop ST-90S guidance was used for the first stage (S-I), after separation the ST-124 and ASC-15 used path adaptive guidance (closed loop) to control the second stage (S-IV). The SA-6 guidance system is shown in Figure 5. The effectiveness of the path adaptive guidance was demonstrated inadvertently when premature shutdown of S-IV engine number eight had virtually no effect on the vehicle trajectory.
The arrangement of the ST-90S and ST-124 systems (including the ASC-15 guidance computer) on SA-6 is shown in Figure 6. This is version 1 of the Instrument Unit, which flew on SA-5, 6, and 7.
On SA-7 the ST-124 system guided the firing of both stages. The guidance and control system for SA-7 is shown in Figure 7. The digital computer is the ASC-15. It replaced both the cam device that contained the S-I tilt program for earlier missions. and the program device that controlled the sequence of events on those missions.
The next mission flown after SA-7 was SA-9. It carried a new version of the Instrument Unit, one that was unpressurized and 2 feet (0.61 m) shorter than version 1. Version 2 flew on the remaining Saturn I missions (SA-8, 9, and 10), and is shown under construction at MSFC in Figure 8. Figure 9 is a blowup of this image, showing the dummy ASC-15 and dummy ST-124.
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