Of the many weapons guidance systems used during the Gulf War, the one with by far the most impact must have been the laser. Though the first laser-guided bombs had been used during the later years of the Vietnam War, it was in the Gulf that they became gold standard for precision guided bombing. Nor was laser guidance only for ordnance dropped from aircraft. US Army attack helicopters used the laser-guide Hellfire missile and US Army artillery fired Copperhead laser-guided artillery shells, although the latter was so expensive that only ninety were used during the entire war.
As important as the laser was to all these precision guided weapons, though, it also had a far more precise and hidden use during the Gulf War. Almost every warplane that flew during the Gulf War was equipped with an inertial navigation system (INS). A precise guide to that airplane’s location even in the absence of navigational signals like GPS, the INS was an essential navigational tool for wartime aviators.
The basic components of each INS are more or less the same: a set of gyroscopes to measure the rotation (and thus the direction) of the vehicle, a set of accelerometers to measure the vehicle’s acceleration, and a computer to integrate the information. In the planes flying in 1991, those gyroscopes were built around a miniature laser. The eerie glow coming from an exposed ring laser gyroscope looks like something from a science fiction movie – military technology blog Foxtrot Alpha says “it looks like something Doc Brown would be working on in his garage.” However, if it hadn’t been for a few lucky breaks and the demands of tens of thousands of economy-class passengers the laser gyro might never have ended up as more than a technological novelty.
The Path to the Laser Gyro
Though the gyroscope was a far older invention, the combination of components that made up an inertial navigation system came together towards the end of the Second World War in the guidance system for the V-2 rocket. They arrived in America after the war, developed by several groups but particularly by Charles Stark Draper and the MIT Instrumentation Laboratory. Inertial navigation systems “drift” as small errors in the measurements by the gyroscopes and accelerometers accumulate and Draper was single-minded in his quest to reduce those errors through advanced design and precision engineering.
The first INSs were expensive and relatively inaccurate but became a vital component of strategic weapons systems, including the first intercontinental ballistic missiles (ICBMs). However, by the early 1960s moderate-cost inertial navigation systems that drifted at rates of only 0.8–1 nautical mile per hour became available for use in military aircraft. Three companies built the majority of them in the United States: Kearfott, Litton Industries (who would later built the INS used in the Air-Launched Cruise Missile and have their Toronto factory bombed as a result), and AC Spark Plug (later AC Delco). A fourth, Honeywell, built high accuracy systems for classified projects such as the SR-71 but failed to seize a substantial share of the wider marked because the technology involved was too classified to be used outside those top secret programs.
The moderate-cost, moderate-accuracy INS quickly spread from the defense sector into the commercial airline market. Early tests by Litton and by Sperry Gyroscope, one of the early gyroscope manufacturers, were followed in 1967 by Boeing’s announcement that AC Delco’s Carousel IV INS had beat out offerings by Kearfott, Litton, and Sperry, as well as Nortronics, to be a standard option on their new jumbo jet, the 747. The following year, American Airlines retrofitted twenty-nine Boeing 707s with INSs built by Litton Industries that had a drift rate of 1.5 nautical miles per hour.
Both expert gyro-builders like Draper and clients like the US Air Force expected the precision of new INSs to grow. The problem was that it wasn’t clear whether that accuracy was either needed or worth the price. Honeywell did successfully sell the Air Force a high-precision INS, accurate to a tenth of a nautical mile per hour, but the Standard Precision Navigator/Gimballed Electrostatic Aircraft Navigation System (SPN/GEANS) only ended up being installed on the upgraded B-52G. As John Bailey told Donald MacKenzie that “we did an awful lot of marketing work on the Strategic Air Command to try to convince them of the advantages of a tenth of a mile per hour system,” and it still took four years and an end-run around standard acquisition procedures to get SPN/GEANS adopted.
As an alternative, INS developers were exploring the idea of a “strapdown” INS, which would abandon the gimballed platform that kept the INS from experiencing the pitch and roll of its platform and instead use the computer to isolate the airplane’s movement through space from its many motions. By omitting the gimballed platform, a strapdown INS would have far fewer moving parts and offer better reliability. Conventional gyros were ill-suited to the demands of strapdown operation so INS developers looked for new gyroscope designs to use instead. The leading contender was the electrostatically suspended gyro (ESG). Unlike traditional gyroscopes that spun a circular rotor on bearings either in gas or fluid, the ESG spun a spherical ball suspended in a vacuum by an electrostatic field. Honeywell, their leading builder, called it “the world’s most perfect gyro.” The Honeywell SPN/GEANS used ESGs to deliver its superior performance, but the technology was also applicable to less precise strapdown applications. Rockwell Autonetics, for example, used the ESG as in their strapdown military INS, the MICRO Navigator (MICRON). By 1974, MICRON was entering the advanced stages of development and the Air Force had budgeted $25 million for full-scale production development.
There was, however, a dark horse in the running to become the heart of the next generation of inertial navigation systems: a “gyro” operating on entirely different physical principles and built around a technology that was itself less than fifteen years old.
To Part Two: Enter the Laser