Skylab was the fourth manned space program of the National Aeronautics and Space Administration to be supported by computers, programs and people of the International Business Machines Corporation during the 20th century.

Computer processing of such data as orbital trajectory and spacecraft monitoring that previously served the Mercury, Gemini and Apollo programs were critical to the success of the Skylab experiments. In addition, both onboard and ground computers helped in the scheduling and execution of Skylab activities.

Special Skylab electronic equipment and programs were produced by IBM in Owego, N.Y. and Huntsville, Ala. Standard IBM installations at the Goddard Space Flight Center, Greenbelt, Md., and the Lyndon B. Johnson Space Center in Houston helped to monitor the Skylab missions with programs developed by IBM. An IBM team was responsible for launch support activities at the John F. Kennedy Space Center in Florida.

Instrument Units

Each launch vehicle used during the Skylab mission employed an IBM-built instrument unit to provide guidance and control functions from launch until earth orbit was achieved.

The instrument unit atop the Saturn V guided the Skylab itself into orbit, and arranged the Skylab's equipment for use by the astronauts when they arrived onboard. The instrument unit also controlled the jettisoning of the protective payload shroud and activated the onboard life support systems, started the solar inertial attitude maneuver, deployed the Apollo Telescope mount at a 90-degree angle and deployed Skylab's solar wings.

In addition, this instrument unit turned on the onboard computers and gave them control of the space station.

Onboard Computers

Two IBM computers in the Skylab controlled the orientation of the laboratory throughout the mission. The lab's solar panels, from which electrical power was obtained, had to face the sun directly to achieve maximum efficiency.

The onboard computers, which were arranged redundantly for added reliability, were models of IBM's System/4Pi, a computer series designed for the special weight and environmental requirements of aerospace applications. They were built at IBM's facility in Owego and fitted and programmed for the mission in Huntsville.

Each of the IBM computers aboard Skylab weighed 100 pounds and measured 19 by 7.3 by 31.8 inches. They were capable of handling more than 100 signals to Skylab attitude control equipment.

Two other electronic units associated with these computers were built by IBM in Huntsville: the workshop computer interface linked the computers with each other and with sensors and control devices; and a memory load unit was able to refresh computer programs in the event of electrical interference disrupting the computers' memories.

Goddard Space Center

IBM's Federal Systems Division developed the Goddard Real-Time System for the Apollo missions. As on Apollo, it was employed on two IBM System/360 Model 75s during the Skylab mission. These computers processed data from radar stations, remote sites and tracking ships which made up NASA's Manned Space Flight Network. IBM personnel at Goddard were responsible for operating and maintaining tracking displays and recording equipment, as they did during the Gemini and Apollo programs.

Lyndon B. Johnson Space Center

At the Johnson Space Center the data facility for ground controllers was called the Real-Time Computer Complex (RTCC). These computers processed the tracking and onboard monitoring data streaming into Houston for the control consoles of NASA engineers. They also accumulated and processed data from Skylab's experiments.

The RTCC, consisting of five Svstem/360 Model 75s, was operated and maintained by IBM. During the Skylab mission, four of the computers had specific functions to carry out, and the fifth machine backed up the other four.

Among the responsibilities of the Model 75s were mission operation computer programs, the Skylab Terminal System, simulation programs and the earth resources interactive processing system.

For additional information on the Skylab program, visit :