The SSEC: IBM’s “Electron Brain” and Reaching the Moon


MAVAC Computer, 1960

Contributed by Josh Hager

The most recent technological innovation to come from the minds at IBM is Watson, a supercomputer designed to understand the syntax of written English when processing queries.  During several recent episodes of Jeopardy! , Watson proved its mettle by defeating two of the most famous human champions in that program’s history, Ken Jennings and Brad Rutter.  While NC State’s Special Collections Research Center does not have the papers of those who designed Watson, we do have a collection that details one of IBM’s major forays into creating a supercomputer designed for incredible computations at (for its time) improbably quick speeds.  Therefore, in honor of Watson’s victory, here is the story of IBM’s Selective Sequence Electronic Calculator (SSEC), the “Original Electron Brain” that made traveling to the moon a mathematical possibility.

On January 27, 1948, a large group of scientists, educators, and civic and business leaders crowded the halls of IBM’s World Headquarters in New York City for the official dedication of the SSEC by IBM president Thomas J. Watson, from whom the newest supercomputer derives its name.  At the time, IBM had been in the supercomputing business since 1915; however, IBM touted the SSEC as the newest leap forward in computational technology.  For example, the SSEC completed calculations 250 times faster than its predecessor (the Automatic Sequence Controlled Calculator finished in 1944).  Of course, the calculating power necessary for such a great processing speed came with a size requirement; the SSEC’s computer panels took up more than 160 feet of wall space in IBM’s headquarters.  Yet IBM did not design the SSEC solely as the acme of arithmetic.  Its function was to calculate the necessary figures needed for scientific research, which explains why representatives from IBM’s Pure Science and Applied Science divisions became crucial employees on the project.  According to IBM’s newspaper, the SSEC could “trace equally well the path of a planet through space, the path of a ray of light through an optical system, or the path of a cosmic ray through the earth’s atmosphere.”  In fact, the inscription on the SSEC, written by Mr. Watson himself, summarized the “mission” of the calculator:  “This machine will assist the scientist in institutions of learning, in government, and in industry to explore the consequences of man’s thought to the outermost reaches of time, space, and physical conditions.”  Surely with such grandiose claims, the team behind the SSEC had a measure of nervousness; the SSEC had to live up to its expectations as one of the greatest contributions to the methodology of scientific research in the 20th century.

Thankfully for the myriad of scientists, engineers, and programmers behind the SSEC, the machine largely performed as well as expected.  One of the SSEC’s first major calculations concerned determining the exact position of the moon relative to earth at any given moment.   While this calculation would allegedly take three weeks with a desk calculator, the SSEC determined accurate data within seven minutes.  The rough estimate of time saved by using the SSEC touted by IBM was that, for four years of intense calculations on the part of a mathematician with a rudimentary calculator, the SSEC could complete the same task in eight hours.  While this specific statistic might have been a marketing hyperbole, it is no exaggeration that the SSEC’s processing power greatly outpaced any other machine of its day.  The SSEC’s sophistication also assisted in answering complex questions; its programming could refer to card-stock tapes of logarithmic and trigonometric data and, with an electronic impulse, pinpoint exact figures to use in advanced equations.  That sophistication was necessary in the moon equation, for example, because many of its components required the use of the sine ratio.

The fact that the SSEC could calculate the exact position of the moon, and inherently derive its distance from Earth, proved invaluable for a mission that the SSEC engineers could not have anticipated.  Sending a spacecraft to the moon required absolute precision.  A slight miscalculation of a percentage point could veer a ship a great distance off course, thereby missing the moon entirely.  This risk actually came to fruition in 1999 when NASA lost a Mars orbiter valued at $125 million due to an incorrect conversion between metric and English units of measurement-the distances calculated for the trip became grossly inaccurate even due to a slight difference in numbers thanks to the vast distances involved.  Thus, without the accurate calculations of the SSEC, NASA could never have envisioned traveling to the moon as the mathematical uncertainties would have posed too great a risk both to ship and crew.  It would be a historical fallacy to claim that IBM through the SSEC was single-handedly responsible for reaching the moon in 1969.  However, the role of the SSEC and its successors in making space travel feasible made Watson’s vision of bringing “man’s thought to the outermost reaches of time [and] space” a reality.

For more information on the SSEC, please see the A. Wayne Brooke Collection, MC 00268,  found online at /findingaids/mc00268 , or visit Special Collections online at /scrc .

Sources:  IBM Business Machines (newspaper), March 15, 1945; “12,000-Tube Electron Brain,” Radiocraft Magazine, May 1948; and various oral histories, all found in the A. Wayne Brooke Collection (MC 00268, Boxes 1-3).