The software ran not on the receiver itself but on the TI Portable Professional Computer (PPC). A quick review of its features illustrates how far both GPS receivers and computing have come. The TI PPC offered 256 kilobytes of random access memory (RAM) and a first-generation Intel 8087 math coprocessor, designed to boost the 8086 central processing unit (CPU), which had a clock-speed rating of five megahertz (five million cycles per second).53 This was the CPU that begat computers bearing the 286, 386, 486, and finally Pentium trademarks. At more than twenty-six pounds, this box and keyboard combo with a nine-inch screen was far from the portability of a laptop computer. Uploading programs and storing information depended on five-and-a-quarter-inch floppy disks. The list price was about $3,000. By comparison, the most expensive smartphones today cost no more than $700, typically have 512 megabytes of RAM—about two thousand times as much computing space—and have CPUS running a billion cycles per second. They wirelessly connect with the Internet to retrieve and display tabular charts like those Satplan created—all while a GPS receiver built on an integrated semiconductor chip small enough to fit into a wristwatch runs unobtrusively in the background, providing continuous data to multiple location-based applications running simultaneously.
Fig. 6.1. Generalized development model by Rockwell Collins. (Courtesy Rockwell Collins)
Fig. 6.2. TI 4100 and antenna by Texas Instruments. (Courtesy Texas Instruments)
Such connectedness was undreamed of in the mid-1980s, but the advance of semiconductor technology and miniaturization of electronic devices was underway. After the TI-4100, the size and cost of GPS receivers began the familiar downward curves associated with most electronic products, but a delay in completing the constellation itself slowed the expansion of GPS applications to other uses, particularly navigation.
A Major Malfunction
The February 1980 GAO report warned about a potential problem that could knock the GPS program off schedule and did so in such a deadpan manner that reading it today is rather chilling: “Space Shuttle problems could also jeopardize DOD’S plan to have NAVSTAR fully operational by 1987. ”54 The catastrophic failure of the space shuttle Challenger seventy-three seconds into its flight on January 28, 1986, undoubtedly exceeded the concerns GAO had in mind. It was the twenty-fifth shuttle mission, officially designated STS-51-L. Although rocket launches routinely experienced technical problems and delays, shuttle missions had become routine—considered safe enough to add schoolteacher Christa McAuliffe to the Challenger crew. Starting with two launches in 1981, NASA successfully launched three missions in 1982, four in 1983, five in 1984, and nine in 1985. Only ten days before the disaster, on January 18, Columbia (which later disintegrated on reentry on February 1, 2003) had completed a six-day mission.55
The Air Force had planned to launch two dozen Block II satellites aboard the shuttle by 1987. Recall, however, that funding cuts in 1980 and 1981 trimmed the constellation size to eighteen and added a year to the schedule. The eighth through eleventh Block I satellites, not designed for the shuttle, flew aboard Atlas rockets from 1983 to 1985. A twelfth Block I satellite, which was removed from the launch schedule and converted into a prototype Block II satellite for test purposes, resides today at the San Diego Air & Space Museum and is the only GPS satellite on public display.56 The grounding of shuttle flights after the Challenger disaster slowed the GPS launch schedule by about two years as the Air Force developed plans to use a new “medium launch vehicle ” called Delta II for the first eight Block II satellites.57 Although it was a new design at the time, the Delta II rocket, as well as launch pads 17A and 17B at Cape Canaveral, traced their lineage directly to the Air Force’s THOR intermediate-range ballistic missile program of 1956.58 Over several decades, the Delta rocket, with subsequent upgrades, has been used extensively for both military and commercial payloads. Between February 14, 1989, and August 17, 2009, Delta II rockets carried forty-eight GPS Block II satellites into orbit.
The second block of GPS satellites consists of four generations or groups of updated and revised designs, with the following designations:59
IIA (“A ” for advanced)—Nineteen satellites developed by Rockwell International were launched between November 1990 and November 1997. Although designed to last seven and a half years in space, two have operated more than twenty years.
IIR (“R ” for replenishment)—Thirteen satellites built by Lockheed Martin were launched between July 1997 and November 2004 to replace previous Block II and IIA satellites that had outlived their design life span. A key improvement in these satellites was onboard clock monitoring, which boosted accuracy and allowed longer intervals between ground station updates.
IIR(M) (“M ” for modernized)—Eight satellites developed by Lockheed Martin were launched between September 2005 and August 2011. This design added a second civilian signal (L2C) for better commercial performance and two new, more powerful military signals with enhanced jam resistance.
IIF (“F ” now stands for follow-on; earlier references used the word future)— The first of twelve IIF satellites, developed by Boeing (which acquired Rockwell International’s aerospace and defense businesses in 1996), launched on May 27, 2010, with subsequent launches scheduled through 2013. These satellites boast a twelve-year life expectancy, more accurate atomic clocks, and a third civilian signal (L5) for improved transportation safety, especially aviation. (A new generation of satellites, Block III, will begin launching in 2015. See chapter 10.)
During the delay in GPS satellite launches resulting from the Challenger disaster, surveying equipment sales kept the commercial market growing and fueled research and development of new GPS applications at a faster rate than would have occurred through defense contracts alone.60 To address problems in the field, advanced techniques and equipment evolved, such as the development of complex interconnected receivers that correct for errors by calculating the differences in signals received at one or more (static) base stations, or precisely known, surveyed positions, with signals from receivers at other, unknown positions, including moving (kinematic) receivers. The development of “differential GPS ” greatly enhanced accuracy and led the way toward land-based augmentation systems that improve navigational accuracy around marine ports and airports.
Fig. 6.3. GPS Block IIA satellite. (Courtesy National Coordination Office for Position, Navigation and Timing)
Smaller, Lighter, and Faster
In 1988 three companies introduced GPS receivers small enough and light enough to hold in one hand. Rockwell Collins, a defense contractor for both GPS satellites and receivers, demonstrated a prototype of the first compact, all-digital receiver, dubbed “Virginia Slim ” after a popular cigarette brand because it was about the size of a pack of one hundred millimeter, or king-size, cigarettes.61 Magellan followed with the first commercial handheld GPS receiver, the NAV 1000, which resembled a walkie-talkie. The device measured about seven and a half inches by three and a half inches, weighed less than two pounds, and could track four satellites by automatically sequencing their signals on a single channel.62 Trimble Navigation offered the Trimpack, a three-channel sequencing receiver capable of tracking eight satellites.63 Trimpack had a slightly larger but flatter design than the NAV 1000. Measuring roughly nine inches wide by two and a half inches tall by eight inches deep and weighing just over three pounds, it could be held by hand or bracket-mounted on a vehicle dashboard or boat instrument panel. Both of these commercial receivers set the stage for broader use of GPS for navigation.
Fig. 6.4. GPS Block IIR satellite. (Courtesy National Coordination Office for Position, Navigation and Timing)
Fig. 6.5. GPS Block IIR(M) satellite. (Courtesy National Coordination Office for Position, Navigation and Timing)
Fig. 6.6. GPS Block IIF satellite. (Courtesy National Coordination Office for Position, Navigation and Timing)
With public use of GPS growing and inquiries about it proliferating, the Pentagon asked the Department of Transportation in 1987 to create an
office to coordinate civilian use. In 1989 the U.S. Coast Guard became the official liaison between military and civil users through creation of the Navigation Center or NAVCEN, located in Alexandria, Virginia. That year the GPS program successfully launched five Block II satellites into orbit.
Fig. 6.7. Trimpack GPS receiver by Trimble. (Courtesy U.S. Army Heritage Museum)
As the 1980s ended, fifteen GPS satellites were in orbit, but the constellation was several years from being complete and declared operational by the Pentagon. Civilian GPS use was increasing, although it was confined largely to specialized tasks due to the size and cost of receivers and the gaps remaining in coverage. The terms Global Positioning System and GPS remained far from household words. It would not be long, however, before GPS got a highly visible public demonstration—a debut with fireworks: the Persian Gulf War.
7
Going to War GPS Aids Military Success in the Persian Gulf
A line has been drawn in the sand.
George H. W. Bush, fifty-fifth presidential news conference, White House briefing room, August 8, 1990
As day broke on January 16, 1991, seven B-52 bombers rumbled more than nine thousand feet down the runway at Barksdale Air Force Base in Louisiana, finally lifting into rainy skies and heading for targets more distant than any bombing run previously ordered.1 After five months of military preparations and diplomatic maneuvering following Saddam Hussein’s August 2, 1990, invasion of Kuwait, Operation Desert Shield was transitioning to Operation Desert Storm.
Not only clouds but also extreme secrecy shrouded the mission. Designated officially as Operation Senior Surprise, the attack from Barksdale carried such a top-secret classification that the several-dozen participants did not even utter its code name. They dubbed the mission Operation Secret Squirrel, a nickname (taken from a cartoon character) for the weapons they carried, which officially did not exist.2 Fifty-seven aviators conducted the mission, with each plane’s crew including two sets of pilots and navigators who exchanged shifts during the nonstop thirty-five-hour round trip. After flying seven thousand miles in fourteen and a half hours, refueling twice along the way, the planes reached designated positions over northwestern Saudi Arabia, where their crews initiated the first combat use of new GPS-guided cruise missiles that had been in development since 1986. The planes carried thirty-nine missiles—most of the existing stock remaining after tests consumed eleven of the original fifty-seven missiles the Air Force had ordered.3 Four of the missiles on the planes experienced software problems and were not launched. The remaining thirty-five missiles were launched at eight targets across Iraq, from Mosul in the north to Basra in the south. The target list, comprising power plants, electric transmission facilities, and military communications hubs, reflected a strategy of swiftly knocking out Iraq’s air defense system and rendering Iraqi command and control “deaf, dumb and blind. ”4
The flight home proved more difficult than the attack phase. Struggling with bad weather, stronger than expected headwinds, engine and radio problems, and the drag of unlaunched missiles, the B-52 pilots had to refuel more often, and the return to Barksdale took more than twenty hours. When they finally touched down the pilots hurriedly taxied the planes into their hangars to keep the unused weapons out of sight.5 This historic combat mission, the first one launched in Operation Desert Storm (though not the first to fire weapons, as attack aircraft already in theater began bombing two hours before the B-52s arrived), was the one the public would learn about last in a war that unfolded with unprecedented visibility on the CNN cable news channel. Operation Senior Surprise remained secret until January 16, 1992, exactly one year later.6
GPS Enters Guided Weaponry
The extra secrecy before and after the mission arose from the missile’s origin and warhead, in addition to its guidance system. Development began after the Air Force accidentally hit the French embassy in Libya with an errant bomb and lost an F-111 fighter and its crew during Operation El Dorado Canyon, an April 1986 raid on Libyan military facilities and terrorist training camps. The Air Force sought a precision weapon that its pilots could launch from safer distances and chose to modify its only standoff weapon, the nuclear-tipped AGM-86B air-launched cruise missile (ALCM). Bomb makers replaced the AGM-86B’S nuclear warhead with a one-thousand-pound conventional bomb and adapted its inertial navigation system for guidance using a GPS receiver in place of the existing terrain contour matching (TERCOM) system. TERCOM uses onboard altitude-sensing radar to compare the terrain beneath the flying missile to topographic maps of the intended flight path stored in its computer.7 Programming each flight is time consuming, and each missile launch must occur very close to its programmed start point, so the system can lock in on the terrain. This works best where the terrain is bumpy and unique. Iraq’s flat desert forced mission planners to send weapons using TERCOM zigzagging among whatever landmarks were available.
GPS, by contrast, provides easier targeting and more launch flexibility. If the missile has precise target coordinates and the receiver can acquire signals, it can determine its location and the route to its destination in the same way a dashboard navigation system will respond by “recalculating ” when the driver veers off the expected path. That sounds commonplace today, but in the mid-1980s there was no precedent for having a single-channel GPS receiver in a missile acquire multiple satellite signals on the fly, much less for having it feed that information seamlessly into an inertial guidance system.8 Boeing engineers overcame those and other technical challenges within twelve months.9 The resulting weapon was the AGM-86C conventional air-launched cruise missile, or CALCM. The missile is nearly twenty-one feet long, two feet in diameter, and has a wingspan of twelve feet. Weighing more than three thousand pounds and powered by a turbofan engine, it can cruise up to 690 miles (its unclassified range) at speeds of 500 mph.10
Anyone knowledgeable about ALCMS who saw the B-52s en route to the Persian Gulf might have reasonably suspected the imminent use of nuclear weapons, since the secret conventional missile looked just like the nuclear version. Extreme secrecy was necessary not only regarding the mission, which gave the Air Force a potent surprise against the adversary, but also regarding the development of the CALCM missiles. Had news of the existence of GPS-guided cruise missiles leaked out, the Iraqi military could have predicted possible attack times. With the GPS constellation incomplete and only sixteen satellites in orbit, there were gaps in coverage, leaving specific windows of opportunity when the required minimum four satellites would be overhead for several hours. Mission planners drew the flight timetable carefully to avoid any possibility that Libyan radar operators might spot the B-52s over the Mediterranean Sea and warn Iraq before the first F-117 stealth fighters attacked.11 Disclosure of the CALCM’S existence could also have complicated negotiations in the Strategy Arms Reduction Treaty (START I), signed July 31, 1991, by President George H. W. Bush and USSR president Mikhail Gorbachev.
Fig. 7.1. AGM-86C/D conventional air-launched cruise missile. The first GPS-guided missiles used by the Air Force were modified AGM-86B cruise missiles with conventional bombs replacing nuclear weapons, but they looked identical. (USAF photograph)
Only seven other GPS-guided missiles were used in the Persian Gulf War—all of them Navy AGM-84 standoff land attack missiles, or SLAMS. That weapon’s development flowed from circumstances similar to those the Air Force experienced in Libya. The Navy sought to put more distance between its pilots and surface-to-air missiles after losing aircraft in raids on Syrian-backed forces in Lebanon during the 1980s. When an A-6 Intruder and an A-7 Corsair were shot down in 1983, the Navy began modifying the twenty-year-old A-6 aircraft and created a new training program for strike pilots.12 After two more A-6 aircraft were lost in 1986, the Navy began developing SLAMS.13 Like the Air Force, the Navy did not start from scratch. The SLAM combined the airframe, turbojet propulsion system, and five-hundred-pound warhead of the Navy’s antiship Harpoon missile with a GPS-aided inertial navigation system and tar
geting technologies borrowed from other missiles. Such targeting technologies included an infrared sensor that transmitted video to the cockpit of an accompanying plane and an electronic data link that allowed the plane’s weapons officer the ability to control the missile’s aim point using the video image.14 The nearly fifteen-foot, 1,400-pound missile could fly slightly more than six hundred miles per hour to hit targets up to sixty-eight miles away. (Newer versions have extended the range to 143 miles.)15 The SLAM was the Navy’s newest weapon when Iraq invaded Kuwait in August 1990; it had never been fired in combat, and fewer than fifty test missiles were available.16 A-6 Intruders from the USS John F. Kennedy in the Red Sea fired two SLAMs at a uranium enrichment plant on the second day of the war, January 18, and fired a third at the same target a week later, on January 25. Aircraft from the USS Saratoga, also in the Red Sea, fired four SLAMs— two from an A-6 Intruder at a Kuwaiti radio tower the Iraqis used for military communications, and two others from an F/A-18 jet fighter at a military building at Taji Airfield, about twenty miles north of Baghdad. Based on the video images these weapons transmitted, four of the seven hit their targets; assessing the damage caused is difficult since the video ceased on impact. Difficulty with the electronic data link and/or loss of GPS signals affected the three missiles that did not perform as expected.17
GPS Declassified Page 13
