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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.

KSC-72P-301 The Apollo Saturn V Instrument Unit is hoisted for mating to the vehicle J.L. Pickering

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.

KSC-70P-359 September 16, 1970 the Instrument Unit is lowered into place atop the Apollo 15 Saturn V launch vehicle Paolo Dangelo

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.
Saturn V Instrument Unit fact sheet.
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.

Apollo6-inVAB-noID Apollo 6 in VAB during installation of Instrument Unit J.L. Pickering

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.


For more information on the computers used in the Apollo project, including Saturn V's guidance & navigation, please refer to the following page.
  • The Apollo Guidance Computer: Architecture and Operation

    Praxis July 11, 2010 USD40.46

    The technological marvel that facilitated the Apollo missions to the Moon was the on-board computer. In the 1960s most computers filled an entire room, but the spacecraft’s computer was required to be compact and low power. Although people today find it difficult to accept that it was possible to control a spacecraft using such a ‘primitive’ computer, it nevertheless had capabilities that are advanced even by today’s standards. This is the first book to fully describe the Apollo guidance computer’s architecture, instruction format and programs used by the astronauts. As a comprehensive account, it will span the disciplines of computer science, electrical and aerospace engineering. However, it will also be accessible to the ‘space enthusiast’. In short, the intention is for this to be the definitive account of the Apollo guidance computer.


  • Digital Apollo: Human and Machine in Spaceflight

    The MIT Press September 30, 2011 USD28.21

    As Apollo 11's Lunar Module descended toward the moon under automatic control, a program alarm in the guidance computer's software nearly caused a mission abort. Neil Armstrong responded by switching off the automatic mode and taking direct control. He stopped monitoring the computer and began flying the spacecraft, relying on skill to land it and earning praise for a triumph of human over machine. In Digital Apollo, engineer-historian David Mindell takes this famous moment as a starting point for an exploration of the relationship between humans and computers in the Apollo program. In each of the six Apollo landings, the astronaut in command seized control from the computer and landed with his hand on the stick. Mindell recounts the story of astronauts' desire to control their spacecraft in parallel with the history of the Apollo Guidance Computer.


  • Saturn V Apollo Lunar Orbital Rendezvous Planning Guide


    Apogee Prime 2011/07/15 USD24.95

    The Saturn V Apollo Lunar Orbital Rendezvous Planning Guide is a reprint of a rare document from the early 1960s in which the whole Apollo moon landing mission was presented and illustrated. The book includes a large fold-out of the Apollo mission as well as a fold-out of the Saturn V moon rocket. It includes illustrations of early iterations of the Lunar Module, maps of the Cape Canaveral launch sites, launch schedules for all of the Apollo test flights, detailed specifications and schematics of the Saturn V launch vehicle stages, construction schedules, engine summaries, information on the VAB, mobile crawlers, Umbilical towers, a DVD and more

    Buy at Amazon.com(US) Buy at Amazon.co.uk(UK)

  • Mission Control

    Mission Control

    Gravitas Ventures 2017/07/27 USD24.99

    At the heart of the Apollo space program and a remarkable decade of achievement was the team who worked in Mission Control.They were born against a backdrop of economic turmoil and global conflict. Some came from a rural lifestyle little changed from the 19th century. Others grew up in a gritty, blue-collar America of mines and smoke stacks. They ranged from kids straight out of college to those toughened by military service. But from such ordinary beginnings, an extraordinary team was born. They were setting out on what JFK called: “The most hazardous, dangerous, and greatest adventure upon which mankind has ever embarked” and through their testimony ? and the supporting voices of Apollo astronauts and modern NASA flight directors ? the film takes us from the faltering start of the program through the Mercury and Gemini missions, the tragedy of the Apollo 1 fire to the glories of the Moon landings.

    Buy at Amazon.com(US) Buy at Amazon.co.uk(UK)