Gemini Guidance Computer
Gemini Guidance Computer in National Air and Space Museum
Invented byIBM Federal Systems Division
ManufacturerIBM Federal Systems Division
Introduced1965 (1965)
Discontinued1966 (1966)
TypeAvionics
Guidance Computer
ProcessorDiscrete Components [1]
Frequency7.143 kilohertz clock
Memory39-bit words memory, each composed of three 13-bit syllables, 4096 words of memory, in a ferrite core array.
PortsModular Display Keyboard (MDK), Modular Display Readout (MDR), Attitude Control and Maneuver Electronics (ACME), Inertial Measurement Unit (IMU), Horizon Sensors, Time Reference System (TRS)[2]
Weight58.98 pounds (26.75 kg)
Dimensions18.9"(H)×14.5"(W)×12.75"(D)

The Gemini Guidance Computer (sometimes Gemini Spacecraft On-Board Computer (OBC)) was a digital, serial computer designed for Project Gemini, America's second human spaceflight project.[3] The computer, which facilitated the control of mission maneuvers, was designed by the IBM Federal Systems Division.[4]

Functionality

Locations of the Gemini Guidance System

Project Gemini was the first with an on-board computer, as Project Mercury was controlled by computers on Earth.[5] The Gemini Guidance Computer was responsible for the following functions:[4][3]

  • Ascent – serves as a backup guidance system. The switchover is manually controlled by the astronauts
  • Orbital flight – gives the astronauts the capacity to navigate, allowing them to choose a safe landing spot in an emergency and calculate the timing of retrofire. (on extended missions ground data may become unavailable when ground data network rotates out of the orbital plane.)
  • Rendezvous – serves as primary reference by providing guidance information to the astronauts. The orbit parameters are determined by the ground tracking which are then sent to the spacecraft; the guidance computer was responsible for processing the information along with sensed spacecraft attitude. The information was presented to the astronauts in terms of spacecraft coordinates.
  • Reentry – feeds commands directly to the reentry control system for automatic reentry or provides the guidance information to the astronauts for manual reentry.

Specs

  • The computer was architecturally similar to the Saturn Launch Vehicle Digital Computer, in particular in the instruction set;[6] however its circuit integration was less advanced.[7] The GGC weighed 58.98 pounds (26.75 kg) and was powered by 28V DC. During a short power outage it could be powered by the Auxiliary Computer Power Unit (ACPU)
  • 39-bit words memory, each composed of three 13-bit syllables[6]
  • Ferrite core memory of 4096 words[8]
  • Two's complement integer arithmetic
  • 7.143 kilohertz clock (140 µs per instruction); all instructions took a single cycle except for multiplication and division

See also

References

  1. ↑ "Ch1-2".
  2. ↑ "The Gemini Spacecraft Computer".
  3. 1 2 McDonnell Corporation, NASA Project Gemini Familiarization Manual, 1965, vol. 2, pp. 8.7,8.45.
  4. 1 2 8. J. C. Hundley and R. A. Watson, "A Digital Computer in Orbital Flight," TR 63-825-892, IBM Federal Systems Division, Owego, New York, October 1964.
  5. ↑ Tomayko, James E. (1988). "The Gemini Digital Computer: First Machine in Orbit". Computers in Spaceflight: The NASA Experience. Washington, D.C.: National Aeronautics and Space Administration. Retrieved 2015-01-04.
  6. 1 2 "Gemini Spacecraft Computer (OBC): Layout of Memory Words". 2016 [2011]. Archived from the original on 2016-05-28. Retrieved 2016-05-28.
  7. ↑ LVDC board reverse engineering project
  8. ↑ Computers in Spaceflight: The NASA Experience, chapter one
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