In 1967, Scott Simpkinson, the Flight Safety Officer for NASA on the Apollo program, had concerns that possibly an unintentional sneak (“surprise”) circuit had caused the fire within the Command Module during the ground test of Apollo 1 that killed astronauts Gus Grissom, Ed White, and Roger Chaffee. As a part of the contract NASA had with The Boeing Company for Technical Integration & Evaluation, Scott initiated a manual analysis effort by electrical system expert engineers to see whether such surprise circuits could be found in Apollo circuits before unintentional activation. This early analysis approach was to have the experienced engineering “trouble-shooters” of electrical problems to examine each system schematic and its associated detail drawings used for manufacturing activity. They were told to look for anything unusual and for any previously unknown operational capabilities, but no specifics of what would indicate such things of concern were given as guidance.

Because of the extreme risk to astronauts and the overall program, the schematics and drawings were examined and signed off by a minimum of three different independent analysts working sequentially. By NASA’s initial definition, sneak circuits were not to include such factors as component failures as initiating events. (That stipulation was later relaxed to an extent due to the significance of previously unrecognized potential problems that were observed during analysis after the more comprehensive topological approach was developed.) The concept of sneak circuits was that they would escape detection during testing phases of the program and lie dormant during initial and normal operations. The “sneaky circuits” would activate only during unusual circumstances and/or multiple failures of components and crew actions. When activated, sneak current would flow through unintended paths to produce unexpected operations or inhibits of desired functions. The cause and effect relationships of the sneak events would normally be mysterious. Such had been the experiences of highly complex and massive electrical control systems in many enterprises, not just in space endeavors.

The initial results of the Boeing-Apollo manual analysis efforts were sparse and led to very little increased confidence that all dangerous sneak circuits were identified. In April of 1968, John Rankin was transferred from Seattle to Houston to evaluate and assist the effort. The first aspect of Rankin’s work was to evaluate the effectiveness of an on-going effort to construct a computerized method called the Cable Loop Identification Program (CLIP). The engineers had theorized that sneaks resulted from unplanned loops in the wiring. However, within a few weeks it was shown that such an approach would be unproductive and highly costly, while resulting in an enormous amount of computer output that would be highly redundant and distracting rather than indicative of any sneak potentials.

In May of 1968, Rankin began to research historical sneak incidents from many industries and then develop a new system to address the root causes of oversights of the problems. The answer seemed to be related to the need for clearer depiction of end-to-end circuitry from primary power sources to actuator loads. The solution was actually a return to the common post-accident investigators’ technique of resolving manufacturing detail back to the topographical sketches similar to diagrams used in teaching electrical engineering students –a type of “reverse engineering” to assure that the final depiction faithfully represents what was actually manufactured. With such topological depictions (called node sets or network trees), it was found that there are a definite set of “clues” to sneak potential that can be associated with the topological patterns at each node. At first empirical clues were extracted from the historical incidents that Rankin had collected. Later, theoretical clues were developed to extend the set for each pattern to cover all known types of electrical circuit elements of the time. These theoretical clues later were proven to apply to other projects as use of the analysis technique spread across all industries and around the world.