Instrument Unit(IU)

IU is the computer system to control the whole of SaturnV. From the ground to the earth orbit, the destination of the rocket is decided by IU.
  • Diameter : 260in (6.604m)
  • Height : 36in (0.9144m)
  • Weight(Average) : 4500lb (2.04ton)
  • Manufacturer:IBM (International Business Machines Federal Systems Div. Huntsville, Ala.)


As for IU of SaturnV, it was based from Saturn I's one, developed by NASA MSFC (Marshall space flight center), manufactured, assembled and tested by IBM. The electronic machine which is necessary for the data transmission, guidance, navigation, tracking were included into IU. The body is composed from three 120-degree aluminum honeycomb segments, and aluminum alloy channel rings are bonded to the top and bottom edge. And there is a spring-loaded door on the umbilical connector.

Environmental Control System

ECS (environment control system) refrigerates the machines put in IU and the top of S-IVB. The 16 cooling boards called "cold plate" are being installed at the IU and S-IVB. The antifreeze-like cooling liquid made from 60% of the methanol and 40% of the water is supplied by reservoir inside IU. Cooling of the cooling liquid is done by ground establishment before launch. About 163 seconds after launch, the sublimation-type heat exchange machine carried on IU starts the work. In such cases as a guidance computer and a flight control computer, the ST-124-M system, in the device which causes a high fever, cooling liquid circulates inside the machine as well to do cooling more efficiently. The cooling liquid and water are made to circulate by the nitrogenous gas.

Guidance and Control

The guidance/flight control computer of IU controls the position of the rocket, a speed, altitude, engine output. The main components of this computer are ST-124-M : Inertial platform, LVDC (Launch Vehicle Digital Computer), LVDA (Launch Vehicle Data Adapter), analog flight computer and gyros. LVDC is the computer system which becomes the center of the control. Various input and output devices (in such cases as the sensor) are connected with LVDC via LVDA. These control devices turns threefold, and when one of the calculation result is different from others, it is ignored. Furthermore, the memory of LVDC turns double, and if an error is detected, it will be corrected with another content.
First, each parameter is set on LVDC before the launch. An inertial platform and LVDC were separated from the ground equipment about five seconds before launch. When a rocket starts rise, inertial platform senses and measures posture and acceleration, and sent the data to LVDC via LVDA. Speed and relative position from the launch are calculated with LVDC from this information. Then, difference of the posture remembered in memory and the actual posture is calculated, the signal to control a posture is generated. This posture control signal is sent to the analog flight computer, with information on gyros, gimbal control of the engine is done. This control is done for about two seconds in the interval.
When the rocket is raised in the atmosphere, guidance system does posture control so that atmospheric pressure may become the smallest. And, IU indicates jettison timing of the S-IC, S-II form amount of the fuel. During the flight by S-II, LVDC controlles the flight course takes suitable for the mission.


To make it the reference of the next mission, the movement of the rocket, air pressure, a noise level, temperature, a vibration, a voltage, electric current, items which reaches several hundred are measured with the sensor, and transmitted as Telemetry to the ground. During the ground, the atmosphere flight, during the space flight, the kinds of the data that is measured are chosen in accordance with the progress of mission, more important datas are transmitted. At the time of the stage jettison, when retro (reverse jetting) rocket works, teremetry falls into the disorder with the influence. Therefore, data are recorded by tape recorder automatically between the stage jettison, and transmitted later.

Tracking System

When the RF pulse signal sent to SaturnV, transpoder on IU receives this, and answer the pulse signal as reply. The position of the rocket can be decided by receiving this in more than one ground station. In SaturnV, AZUSA, C band radar, S band command & communication system, three kinds of tracking systems are carried. Memory dumping and memory rewriting of the computer on IU can be done through this system.

Electrical System

The power is supplied from the ground equipments before the launch via the umbilical connector. Then, about 25 seconds before of the launch, four DC28V batteries carried on IU takes over this. During the flight, to save electric power, the equipments that doesn't need immediately are cut off by LVDC and LVDA.

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