IBM was heavily involved in the Apollo missions, providing computers for multiple ground locations including Cape Canaveral, Florida, and Houston, Texas, Mission Control Center. Perhaps the most visible contribution, however, came in the form of the instrument unit or guidance system for the famed Saturn V rocket that propelled humans to the Moon.

Designed by NASA, and built and programmed by IBM at the Space Systems Center in Huntsville, Alabama, the Saturn instrument unit (IU) was the computer nerve center for the launch vehicle—controlling the Saturn rocket until Apollo was safely headed to the Moon. It determined when to fire the Saturn’s three rockets, when to jettison them and where to point them. Included in the IU’s equipment complex were devices to sense altitude, acceleration, velocity and position, as well as the computer to lay out the desired course and give control signals to the engines to steer the Saturn on that course.


4 men working inside the Saturn V instrument unit
Manufacturing the Saturn V instrument unit

A view of the Saturn V instrument unit being manufactured in the east high bay at IBM in Huntsville, Alabama. IBM was the prime contractor for development and fabrication of the instrument unit—a vital piece for the proper flight of Apollo 11. It contained navigation, guidance, control and sequencing equipment for the launch vehicle and would be mounted atop the third stage rocket between the Saturn V and the Apollo spacecraft.

2 men inside the Saturn V instrument unit
Testing the Saturn V instrument unit

Here, IBMers conduct a systems test on the instrument unit. Beyond guidance systems, the instrument unit also provided command and sequence of vehicle functions, telemetry and environmental control.

Men working as the instrument unit is lowered
Setting the stage

IBM’s instrument unit is lowered into place atop the third stage rocket in the vehicle assembly building at the NASA Kennedy Space Center. The Apollo spacecraft will later be installed directly above the instrument unit.

Diagram of the Saturn V instrument unit with labels for all the components
Diagram of IBM’s instrument unit

This illustration shows the major components of the instrument unit and their configuration. The instrument unit kept the Saturn V launch vehicle properly functioning and on its course, sending the first men to the Moon. The instrument unit was essentially the same in both the Saturn IB and the Saturn V.

Diagram of the instrument unit production sequence
Production sequence

The instrument unit was composed of three 120-degree segments, each consisting of thin-walled aluminum alloy face sheets bonded over a core of aluminum honeycomb. The instrument unit’s guidance and control system navigated the skies by determining vehicle position and velocity from measurements made on board, guided the vehicle by computing maneuvers necessary to achieve the desired trajectory, and controlled the craft by executing maneuvers to control proper hardware.

Diagram of the Saturn launch vehicle and which contractors contributed to each part
Contractors’ contributions to the Saturn V

This diagram shows the major NASA contractors and their contributions to the Saturn launch vehicle. IBM’s instrument unit is positioned at the top of the third stage rocket, between the launch vehicle and the Apollo command, service and lunar modules.

PDF Cover page: Saturn IB News Reference Instrument Unit Fact Sheet
The Saturn V instrument unit fact sheet

Overall responsibility for construction of the instrument unit was assigned to IBM’s Federal Systems Division. This division was accountable for the fabrication and assembly of the unit, system testing, and integration and checkout of the unit with the launch vehicle. The instrument unit contained electrical equipment necessary for guidance, tracking and communication of the Saturn V’s environmental and performance data.


Men working at the Real-Time Computer Complex
IBM’s Real-Time Computer Complex at NASA, Houston

The Real-Time Computer Complex (RTCC) in Houston, Texas, was an IBM computing and data processing system at NASA’s Manned Spacecraft Center—now called the Lyndon B. Johnson Space Center—that collected, processed and sent to Mission Control information to direct every phase of an Apollo mission. The RTCC was so fast, there was virtually no time between receiving and solving a computing problem. Initially, IBM 7094-11 computers were used in the RTCC. Later, IBM System/360 Model 75J mainframes, and peripheral storage and processing equipment were used.

Men discussing numeric keyboard to the guidance computer
The guidance computer

In 1965, for the first time, a guidance computer rode into space with astronauts and was used to supply flight information so command pilot Virgil E. Grissom could maneuver his spacecraft. The success of the three-orbit Gemini III mission, one of the key steps in the US program to put men on the Moon, demonstrated the reliability of the 59-pound (27-kg) spacecraft computer made at the IBM Space Guidance Center.

Man working on part of the Saturn digital computer
Saturn digital computer

The Saturn computer and data adapter, designed and manufactured by IBM’s Electronics Systems Center in Owego, New York, were part of the launch vehicle guidance system. The IBM digital computer issued signals 25 times a second to help keep the Saturn on course during launch, and was primarily responsible for prelaunch checkout, booster guidance and Saturn V lunar trajectory injection.

Apollo flights had so much information to relay, that their computers had to report in an electronic form of shorthand. Even in shorthand, however, it took a circuit capable of transmitting a novel a minute to get the information to NASA’s Manned Spacecraft Center—now the Johnson Space Center—in Houston, Texas. Receiving this enormous amount of data was a powerful IBM computer whose sole task was to translate the shorthand into meaningful information for Apollo flight controllers. The IBM System/360 computer absorbed, translated, calculated, evaluated and relayed this information for display. It was one of five System/360 machines used by NASA for the Apollo 11 mission. The same System/360 computer that processed the data for the first lunar landing from 240,000 miles away in Houston, also calculated the liftoff data needed by astronauts Neil Armstrong and Edwin “Buzz” Aldrin to rendezvous back with the command module piloted by Michael Collins for the flight back to Earth.

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