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EAI PACE 231R (NASA, 1960).jpg
PACE 231R, NASA/Glenn Research Center, 6/6/1960
Developer Electronic Associates
Manufacturer Electronic Associates
Product family PACE Series
Type analog computer
Release date 1958[1]
Introductory price $20,000-1,000,000[1]

Operating Range +/- 10V
  • 100-324 Op-Amp
  • 150-320 Pots
  • 20-42 Multipliers
  • 20-34 Function Generators
  • Multimeters
  • Power Racks
  • Sets of removable patch panels

The PACE 231R was an analog computer developed by Electronic Associates in 1958[1]. The 231R was EAI's flagship computer becoming the most widely used analog computer system in the world - operating in various places well into the late 1970s and even early 1980s.

The EAI 231R is notable for having been used for simulation in many of the early space and aviation projects including the Project Mercury, Project Gemini, and the X-15.


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Notable installations/applications[edit]


X-15 Simulator

In 1956, during the development of the North American X-15, no digital computer had the performance capabilities of delivering flight simulation calculations in real time which is why NASA chose the EAI PACE 231R analog computer instead. Three EAI 231R computers, containing 380 operational amplifiers, 101 function generators, 32 servo amplifiers, and 5 electrical multipliers networked together made up the simulator. The simulator covered 0.2 to 7.0 Mach at altitudes from sea level to 1,056,000 feet. It was not, however, capable of providing meaningful landing simulations. [2]


HL-10 Flight Simulator.

Flight Research Center's first HL-10 simulations was done with the PACE 231R. As they described "The real capability of the analog computer was its ability to integrate differential equations. Because the equations of motion for the lifting bodies were differential equations-as are all equations of motion for aerospace vehicles-the simulation engineers mechanized them on available analog computers."[3]

Langley Research Center / Project Mercury[edit]

In June 1960 EAI won a $1.51M contract to supply NASA's Langley Research Center with five fully expended PACE 231R systems. Those systems were used for various aspects of the Mercury project, including space station rendezvous. It was also used for the simulation of missile launches and satellites.[1]


  • NASA
    • Goodard Space Flight Center, Washington DC
    • Space Task Unit, Langley Research Center
    • Ames Research Center, Moffet Field
    • Manned Space Flight Center, Houston Texas
  • United Kingdom Atomic Energy Authority
    • Dragon reactor[4]
    • Steam-generating heavy water reactor (SGHWR)[4]


Photo From the 1958 Brochure.


  1. 1.0 1.1 1.2 1.3 Small, James. S. The Analogue Alternative: The Electronic Analogue Computer in Britain and the USA, 1930-1975. (2013). Routledge. ISBN 9781134699025.
  2. Jenkins, Dennis. R. X-15: Extending the Frontiers of Flight. (2012). NASA (EBook). Retrieved 12 20, 2015, from
  3. Reed, Dale. R.. (1997, August) "BACK TO THE DRAWING BOARD". SP-4220 Wingless Flight: The Lifting Body Story. Retrieved 12 22, 2015, from
  4. 4.0 4.1 Fry, Peter. Remembering AEE Winfrith: A Technological Moment in Time. (2015). Amberley Publishing. ISBN 9781445654799.