Saturn Launch Vehicle Digital Computer

The Launch Vehicle Digital Computer ( LVDC ) was the control computer of the Saturn V and Saturn IB rockets. It was one of the main components of so-called instrument unit, an annular arrangement of devices, which was located at the top of the third stage (S- IVb) Saturn V and the second stage ( S- IVb) Saturn IB. The main task of LVDC was the flight control of Saturn from the start to reach Earth orbit. In addition, he supported before and after the start of functional testing of individual components Saturn. Was developed and built the LVDC of the IBM Federal Systems Division.

Description

Hardware

The LVDC worked with a clock frequency of 2.048 MHz ( an addition needed a time of 82 microseconds ). Its memory - that was designed as a toroidal-core memory - had a maximum capacity of 32,768 28-bit data words in memory modules to 4096 data words. The LVDC worked with 26-bit data words ( 25-bit data and 1 sign bit) with 2 additional parity bits for error detection. The instructions had a length of 13 bits with a parity bit. Thereby fit two instructions in a data word, whereby the programs required less space, which was advantageous because of the low storage capacity.

For reasons of reliability in the LVDC logic was designed and organized in seven steps with a downstream triple redundant voting system at any stage. This meant that one could fall out of three logic modules on each of the seven stages, and the LVDC nevertheless produced a correct result. Thus, the LVDC had an estimated reliability of 99.6 % at 250 hours of operation.

The LVDC had a size of 74 cm x 32 cm x 27 cm, weighed 35 kg and had a power consumption of 137 W.

Software

The 13-bit wide instructions of the software LVDC consisted of a 4-bit wide operator and a 4-bit wide address field. Thus 16 different instructions were possible. However, since there were 18 statements used three statements the same operator, and two bits of the address field to determine which should be carried out of the three statements.