Stakes in the Sand: Surveying in the Gulf War

In 1990, US forces arrived in the Persian Gulf with a cornucopia of navigation technologies: not just GPS but also LORAN, TACAN, TERCOM (for cruise missiles), and inertial navigation systems which used laser, electrostatic, or mechanical gyroscopes, as well as old-fashioned manual tools like maps and compasses. So why were US surveyors heading off into the Saudi desert?

The surveyors were from the 30th Engineers Battalion (Topographic), which was deployed to provide map production and distribution, surveying, and terrain analysis services to the theatre. The survey platoon’s work was being done on behalf of the Corps and divisional artillery, which had their own particular navigational needs. Unlike fighter or helicopter pilots, field artillery gunners didn’t have the opportunity to see their targets and make last-minute adjustments to their own aim. Unlike bomber crews or cruise missiles, their fire missions were not planned well in advance using specialized materials. To provide precise positioning information to the guns, each artillery battalion in the Gulf was equipped with two Position and Azimuth Determining Systems (PADS), truck-mounted inertial navigation systems that keep an ongoing track of the unit’s positions. At the heart of the PADS was the standard US Navy inertial navigation system, the AN/ASN-92 Carrier Inertial Navigation System (CAINS).

Like all inertial navigation systems, PADS had a tendency to drift over time. That meant that it required regular refreshes using a pre-surveyed location, or control point. The initial specifications for PADS were to achieve a horizontal position accuracy of 20 meters over 6 hours and 220 kilometers. Actual horizontal accuracy seems to have been far better, more like 5 meters. One reason for the high accuracy was that, unlike an airplane, the vehicle carrying the PADS could come to a complete stop, during which the system detect and compensate for some of the errors by the accelerometers in the horizontal plane.

Unfortunately, the US had exactly one control point in Saudi Arabia, at Dharan airbase (Army Reserve historian John Brinkerhoff says this and several other point surveyed were done with “Doppler based methods.” I assume that means using the TRANSIT satellite system, which determined location on the basis of Doppler shift). Starting from that control point, the 30th’s surveyors extended a network of new control points northwards and westwards towards the Iraqi border. Conventional line-of-sight survey methods would have been too slow, but the surveyors had received four GPS receivers in 1989 and soon got more from the Engineer Topographic Laboratories to equip a follow-up team of surveyors. Eventually, their survey covered 10,000 square kilometers and included 95 control points. Relative GPS positioning took about two hours (according to Brinkerhoff) and offered accuracy to about 10 centimerers (compared to 17 meters for regular GPS use). Absolute positioning – done more rarely – required four hours of data collection and provided accuracy of 1–5 meters.

When the ground war began on 24 February 1991, the two survey teams tried to stay ahead of the artillery, which meant driving unescorted into the desert and marking new control points with steel pickets with reflectors (for daytime) and blinking lights (for night-time). Providing location data through headquarters was too slow, so the surveyors took to handing it directly to the artillery’s own surveyors or just tacking it to the pickets. By the ceasefire on March 1 they had surveyed all the way to 30 km west of Basra. Where the artillery outran the control points they used their own GPS receivers to make a “good enough” control point and reinitialized the battalion PADS there, so all the artillery batteries would at least share a common datum. One thing PADS could do and GPS couldn’t was provide directional information (azimuth), so units that outran their PADS capabilities had to use celestial observations or magnetic compasses to determine direction.

What the 30th Battalion and the artillery’s surveyors did in the Gulf was different enough from traditional survey methods that the some in the army already used a different phrase, “point positioning,” to describe it. In the 1968–1978 history for the Engineer Topographic Laboratories, which designed army surveying equipment, PADS was one of three surveying and land navigation instruments singled out as part of this new paradigm (the others were a a light gyroscope theodolite with the acronym SIAGL and the Analytical Photogrammetric Positioning System).

Brinkerhoff tells the story of the 30th’s surveyors as the meeting of the high and low tech, but the work really relied on a whole range of technology. Most of the GPS surveying was relative positioning that was anchored to previous Doppler surveying. Position and azimuth information was carried forward by inertial navigation, and the position of the firing battery was paired with target information from a forward observer equipped with GPS, an inertial navigation system, or a paper map or from aerial photography which could be interpreted using the aeroplane’s own navigation system or a photointerpreter’s tool like APPS. GPS surveying and navigation did not stay wrapped up with all these other navigational tools for long. The technology was flexible enough to be used in place of many of them. But in the early 1990s, GPS’s success was contingent on these other systems too.

Sources Notes: The story of the 30th and its surveyors appears in John Brinkerhoff’s monograph United States Army Reserve in Operation Desert Storm. Engineer Support at Echelons Above Corps: The 416th Engineer Command (printed in 1992). Further details appear in the Army Corps of Engineers history Supporting the Troops: The U.S. Army Corps of Engineers in the Persian Gulf War (1996) by Janet A. McDonnell and “The Topographic Challenge of DESERT SHIELD and DESERT STORM” by Edward J. Wright in the March 1992 issue of Military Review. Reflections on how the artillery used PADS and GPS in the Gulf come from the October 1991 issue of Field Artillery, a special issue on “Redlegs in the Gulf.” Technical details for PADS are from the ETL History Update, 1968–1978 by Edward C. Ezell (1979).

The Other Lasers of the Gulf War, Part Three

Part of a three-part series on the development of the laser gyroscope and its military use. Back to Part Two or Part One

Meaning and Legacy
Sociologist Donald MacKenzie, whose book Inventing Accuracy remains pretty much the classic history of inertial guidance development, convincingly argues that there was nothing inevitable about the choices made in the development of these inertial navigation systems. After all, despite widespread military adoption in the mid-1980s, the laser gyro was hardly the only game in town. Despite granting $135 million in development funds to design laser gyro guidance systems for the abortive Small ICBM (aka the “Midgetman”) the US Air Force decided that the laser gyro wouldn’t meet the requirements and borrowed the mechanical gyro system used in the MX ballistic missile instead. Likewise, the F-117 stealth fighter entered service with the precise but off-the-shelf SPD/GEANS INS. Instead, the decisions to fund, buy, and develop technologies like the laser gyro reflected the strategic plans, aspirations, and expectations of technologists and users, as well as sheer coincidence. Charles Stark Draper was right that mechanical gryos would continue to be and to become more accurate for the foreseeable future, but the laser gyro had the promise of a radical technological breakthrough and the sexiness of the very word laser.

The case of the laser gyro also shows how tough it is to pigeonhole a technology as “military” or “civilian” in its origins. Is the laser gyro military technology because much of the initial development money came from military sources? Is it civilian technology because it was the commercial airliner industry that first bought them en masse and made the transition from prototype to standardized product? Does tracing that history help us understand how precision navigation contributes to either sphere of action?

I started looking at the navigational tools applied during the first Gulf War because of Ingrid Burrington’s article on a 1990s protest against GPS because of its military origins (which I commented on here). Writing in the Atlantic, Burrington describes how activists Keith Kjoller and Peter Lumsdaine snuck into a Rockwell International facility in Seal Beach, California and used wood-splitting axes to smash up nine GPS satellites “to slow the deployment of this system (which) makes conventional warfare much more lethal and nuclear war winnable in the eyes of some.”

Interviewed by Burrington twenty-two years later, Lumsdaine was firm that GPS remains “military in its origins, military in its goals, military in its development.” What I wanted to investigate was what that meant in comparison to all the other systems that contributed to the type of aerial campaign launched in the Gulf. Along the way examples dropped into my lap of similar protests against those technologies. Mass opposition to the installation of transmission towers for the Omega radionavigation aid, as opposed to the more precise and more military-used Loran-C. The bombing of a factory for the inertial navigation systems of the Air-Launched Cruise Missile.

Trying to parse the role of the laser gyroscope in the first Gulf War is tough because it was so widespread. I can’t find anyone who writes about using an INS in the Gulf, perhaps because it was such a mundane occurrence. But the development path of the laser gyro shows that calling it a military technology involves making some presumptions about whose contributions mattered. Early inertial navigation was bought and paid for by the military because of its use in strategic (i.e. nuclear) weapons, but within twenty years had trickled down into commercial aviation. The laser gyro was similarly funded in its development by the armed forces, but they went on to shun it as an initial product because it was not yet superior to what they had in service. It was commercial aviation, the previous trickle-down beneficiary, who put up the funds to turn the laser gyroscope into a practical and widespread device. This was technology that was normalized as civilian before it was normal in the military.

Perhaps not coincidentally, alongside the GPS receiver you probably carry in your pocket you also have a set of accelerometers and gyroscopes. Most modern smartphones include microelectromechanical (MEMS) inertial sensors to measure orientation and motion, which is used to do things like change the screen orientation when you turn your phone sideways. (This is a very cool video that explains how a MEMS accelerometer works and how it is manufactured.) Should you be concerned that you’re carrying around a miniaturized, albeit inaccurate, version of the technology mounted on the first ICBMs? Quite possibly, considering that researchers have shown how the gyroscopes in a phone could be used to eavesdrop on nearby audio or keystrokes. But probably not because it was the US Department of Defense that funded its origins.

Source Notes: Not much has been written about the history of gyroscope development. The notable exception is Donald MacKenzie’s exceptional history Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance. MacKenzie’s history of the laser gyroscope is a separate article, “From the Luminiferous Ether to the Boeing 757: A History of the Laser Gyroscope” (Technology and Culture, July 1993). Paul G. Savage’s paper “Blazing Gyros – The Evolution of Strapdown Inertial Navigation Technology for Aircraft” (originally published in Journal of Guidance, Control, and Dynamics, May/June 2013) was also very useful. Given the absence of broader histories, Flight magazine’s archive was very useful for filling in some details.

The Other Lasers of the Gulf War, Part Two

Part of a three-part series on the development of the laser gyroscope and its military use. Back to Part One

Enter the Laser
Despite its name, a laser “gyroscope” does not use a rotating mass to measure angular momentum. Instead, it takes advantage of the Sagnac effect, the fact that two beams of light sent in opposite directions along a rotating circuit will travel slightly different distances and thus end up slightly out of phase. Measuring the phase difference lets you determine the rate of rotation. Using a laser made the effect measurable for practical applications. The first practical demonstration of the technology was made by a team at Sperry Gyroscope in January 1963, just under three years after the Hughes Research Laboratories demonstrated the first functioning laser. Other instrument designers such as Kearfott, Honeywell, Autonetics, and Draper experimented with the technique too – Draper considered it a distraction from perfecting his floated gyros, which had far better accuracy.

Like strapdown INSs in general, the laser gyroscope’s lack of moving parts seemed to offer better reliability. Its use of laser beams also had the promise of potential performance beyond the physical limits of conventional gyroscopes. Still, in the early 1970s the technology was by no means mature. Despite its future promise, the laser gyroscope remained less accurate and less reliable than more mature gyroscope designs.

Though several companies continued to develop laser gyros, the most successful of them was Honeywell, where there was no major existing INS business that had to protect its turf. With some funding from the US Naval Weapons Center Honeywell’s Florida division built the Advanced Tactical Inertia Guidance System (ATIGS) in 1974. Mounted in a pod on a Navy A-7 attack aircraft, the Honeywell system showed drift rates in the range of 5–10 nautical miles per hour, not nearly as good as current production systems. Honeywell’s Minneapolis division was already designing a strapdown inertial system for the aviation market using a conventional floated gyro, and it now switched to the laser gyro. Before flight testing at Holloman Air Force Base, the Minneapolis team spent $30,000 to install the prototype in a GMC RV. Having demonstrated a circular error probability of 0.9 nautical miles per hour in flight tests, Honeywell took the laser gyro INS on the road, still in the van, to demonstrate it to potential customers. The Department of Defense gave Honeywell $8.5 million to develop a prototype that would meet both the 1 nautical mile per hour drift requirement and the form-fit-function (or F3) requirements for fitting into military aircraft. What did not happen after the Holloman AFB tests was a flood of military orders for production systems. Nor, in fact, were there any orders for laser gyroscopes at all. The technology remained both unproven and less precise than other systems.

Salvation for laser gyro came from an unexpected direction: Boeing’s commercial aviation division, which was beginning to design its next generation of airliners, the 757 and 767. Despite its various disadvantages, the laser gyro had several features that made it particularly attractive in this situation. The laser gyro’s output was digital rather than analog, which made it a good fit with the new, increasingly computerized avionics Boeing planned to use. Its high reliability due to the lack of moving parts would offer cost savings in maintenance and replacement, something Boeing was keen on. Lastly, as MacKenzie explains it, “the sheer glamour of the laser gyro was appropriate to the ‘high-tech’ image of the 757 and 767 that Boeing was cultivating.” Relative imprecision was an acceptable price to pay under the circumstances. Getting laser gyroscopes into Boeing airliners required the engineers involved not only to sell their senior management on the still unproven gyro, but also ensure that the multi-company committee that set specifications for commercial avionics would approve specs that accommodate physically larger inertial navigators, since laser gyros had not yet been miniaturized to match the latest generation of mechanical gyros. Boeing signed its contract with Honeywell in November 1976, delivered its first prototype unit in 1979, and the first production units in 1981. Once Boeing made the Honeywell gyro standard on the forthcoming 757 and 767, Airbus quickly followed, putting a Litton laser gyro on the Airbus A310.

Despite the commercial breakthrough, success in the military market was slow coming. Though Honeywell offered a laser gyro-based INS in the competition to provide an INS for the AV-8B, the US Marine Corps chose a conventional mechanical system in 1983. By then, Honeywell’s commercial systems were racking up 10,000 hours of flight time every week. The first US military contract was for Litton’s LTN-90, to be on the Boeing E-6A, a Navy strategic communications airframe. Even then, the laser gyros were only to be used as inertial reference sensors, not in an integrated navigation system. The floodgates only opened in 1985, when Honeywell got an $8.8 million production contract for laser gyro INS to be used in F-15s, F-111s, RF-4Cs, C-130s, and HH-60s. Litton and Kearfott got contracts to build laser gyros for the US Navy, and Litton also received an $11.8 million contract to supply the same gyro used on the E-6A for F-15E. Soon enough, most military aircraft were flying with an INS that relied at its core on a laser gyroscope.

To Part Three: Meaning and Legacy

The Other Lasers of the Gulf War, Part One

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