Saturn V Instrument Unit

The Saturn V Instrument Unit is a ring-shaped structure fitted to the top of the Saturn V rocket's third stage (S-IVB) and the Saturn IB's second stage (also an S-IVB). It was immediately below the SLA (Spacecraft/Lunar Module Adapter) panels that contained the Lunar Module. The Instrument Unit contains the guidance system for the Saturn V rocket. Some of the electronics contained within the Instrument Unit are a digital computer, analog flight control computer, emergency detection system, inertial guidance platform, control accelerometers and control rate gyros. The instrument unit (IU) for Saturn V was designed by NASA at Marshall Space Flight Center (MSFC) and was developed from the Saturn I IU. NASA's contractor to construct the Saturn V Instrument Unit was International Business Machines (IBM).

One of the unused Instrument Units is currently on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia. The plaque for the Unit has the following inscription:

The Saturn V rocket, which sent astronauts to the Moon, used inertial guidance, a self-contained system that guided the rocket's trajectory. The rocket booster had a guidance system separate from those on the command and lunar modules. It was contained in an instrument unit like this one, a ring located between the rocket's third stage and the command and lunar modules. The ring contained the basic guidance system components—a stable platform, accelerometers, a digital computer, and control electronics—as well as radar, telemetry, and other units.

The instrument unit's stable platform was based on an experimental unit for the German V-2 rocket of World War II. The Bendix Corporation produced the platform, while IBM designed and built the unit's digital computer.

There was no Instrument Unit for Saturn I Block I boosters (SA-1 to SA-4). Guidance and control equipment was carried in canisters on top of the S-I first stage, and included the ST-90 stabilized platform, made by Ford Instrument Company and used in the Jupiter missile.

The IU made its debut with SA-5, the first Saturn I Block II launch. The first version of the IU was 154 inches (3,900 mm) in diameter and 58 inches (1,500 mm) high, and was both designed and built by MSFC. Guidance, telemetry, tracking and power components were contained in four pressurized, cylindrical containers attached like spokes to a central hub.

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