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Military


Joint Direct Attack Munition (JDAM)
Anti-Jamming Countermeasures/Programs

GPS is widely used as a source for position, velocity, and time information on U. S. military platforms. However, the GPS signal is of low power and vulnerable to interference. Threats range from cheap, expendable, low-power jammers that can be widely distributed across an area of conflict, to medium and high-power ground and air-based jammers that can deny usage of GPS over hundreds of miles. The GPS Joint Program Office established the Navigation Warfare (NAVWAR) program in 1996 to address the electronic warfare threat to the GPS system. The NAVWAR program was tasked with protecting DoD and allied use of GPS during times of conflict, preventing its use by adversaries, and maintaining normal availability to the civil user outside the area of conflict.

Anti-Jam GPS Technology Flight Test (AGTFT) Program

As part of the U.S. Air Force's Anti-Jam GPS Technology Flight Test (AGTFT) program, an antijam GPS/inertial navigation system (INS) guidance/navigation system using a modified JDAM was designed, fabricated, ground and free flight tested. The key objective of the program was to demonstrate the performance and technology maturity of a high-antijam GPS system, for the lowest incremental cost, added to a smart munition-the JDAM.

The AGTFT program modified a JDAM tail kit to add a low-cost GPS antijam system that can be easily added to other air-to-ground weapons. The program proved that the system operates satisfactorily against a high-level jamming environment in the target area. On four AGTFT free flights, the AGTFT flight test vehicles (FTVs) hit within a circular error probability (CEP) of 4.4 meters with the Target Location Error (TLE) not included. Factoring in a 7.2 meter TLE, the CEP is 8.4 meters. The miss distance from the target pole did not exceed 6.7 meters under a high-jamming environment. The FTVs were dropped from 44,000 feet mean sea level (MSL) and at a range of approximately 9 nautical miles (NM) from the target pole. The AGTFT design is physically and functionally mature.

The anti-jam Global Positioning System (GPS) was developed by Boeing successfully defeated jammed environments in two successive drop tests in 1998, thus allowing the test vehicles to strike well within their designated target areas. The drop tests were performed at the White Sands Missile Range in New Mexico using modified Joint Direct Attack Munitions (JDAMs) as test vehicles.

The objective of the AGTFT program was to develop and demonstrate a low cost solution to the potential jamming vulnerability of GPS-aided, inertially guided tactical weapon systems. Candidates for the new system included JDAM and the Conventional Air-Launched Cruise Missile (CALCM).

The Boeing solution, developed in the Phantom Works, consisted of a Harris Corp. anti-jam electronics module integrated with a closely coupled GPS/INS (inertial navigation system) guidance unit and an anti-jam GPS antenna, both produced by Boeing. The GPS receiver was provided by Collins and the inertial measurement unit by Honeywell.

The system decveloped by Boeing was built on the experience acquired as part of the Air Force's Tactical High Anti-Jam GPS Guidance (THAGG) and Tactical GPS Anti-Jam Technology (TGAT) and JDAM programs. This enabled the production of a low cost system that defeats high jamming environments while maintaining high weapon accuracy.

In the first test, the AGTFT test vehicle was dropped from 44,000 feet into a low-power GPS-jammer environment and achieved direct military code GPS acquisition within 12 seconds. The test vehicle descended in the jammed environment through wind shears of up to 105 mph, continuously tracking GPS satellites and striking within 3 meters of the target. During the second test, the AGTFT test vehicle was dropped into a high-power GPS-jammer environment from 44,000 feet and achieved direct military code GPS acquisition within 8 seconds. While descending through wind shears of up to 110 mph, the test vehicle continued to track GPS satellites in the jammed environment and ultimately struck within 6 meters of the target.

The four-phase AGTFT program was awarded to the former McDonnell Douglas (now Boeing) in August 1995. Anti-jam (AJ) subsystem hardware testing was conducted during Phase I; AJ subsystem integration into eight flight test vehicles was performed in Phase II; and system level AJ ground testing of a flight test vehicle occurred in Phase III. Six more drop tests are scheduled through May to complete Phase IV.

The Air Force Research Laboratory (AFRL) Munitions Directorate at Eglin Air Force Base, Fla., lead the AGTFT program, valued at approximately $6 million. The technology used to create and verify the GPS jamming environments for these tests was developed under the direction of AFRL at Eglin over the past six years.

The delta to JDAM unit cost is estimated to be $6,000 for small numbers (5,000 units). This unit cost delta would be reduced if antijam became part of the baseline JDAM production configuration and the quantities of antijam devices were increased.

The Anti-Jam GPS Technology Flight Test (AGTFT) program completed in 1998.

As of September 2002, the Air Force Research Laboratory Munitions Directorate's Navigation and Control Branch (AFRL/MNGN), with support from Boeing GST, had conducted two free-flight test missions to demonstrate a new autopilot technology aimed at reducing the dependence on wind tunnel testing for flight demonstrations, munition configuration upgrades, and pre-planned product improvement developmental programs The test missions relied on the use of updated Anti-Jam Global Positioning System (GPS) Technology Flight Test (AGTFT) MK-84 tail kits.

As of early 2003, it was unclear whether the antijam had been integrated into JDAM unit production.

Global Positioning System (GPS) Guidance Package (GGP)/GPS Experiments (GPX)

The thrusts of the Global Positioning System (GPS) Guidance Package (GGP)/GPS Experiments (GPX) program are to develop and demonstrate technologies for affordable, robust guidance, navigation, and control. These technologies will be applicable both to new and retrofit packages in a variety of applications including ground vehicles, airborne platforms, air-to-surface weapons, and surface-to-surface standoff weapons.

The GGP Program will develop and mature solid-state Miniature Inertial Measurement Unit (MIMU) technologies for affordable, precise navigation. The program combines and tightly couples the all solid-state MIMU with a miniature GPS receiver (MGR) to exploit known mutual synergisms. Specific quantified goals for integrated GGP units are:

  • MIMU accuracy = 1 nmi/hr; less than or equal to 20m after loss of GPS signals for 4 minutes.
  • MGR accuracy 16 m spherical-error-probable (SEP).
  • Volume = 135-170 in3; Weight = 7-10 lb; Power = 25-30 W; $15 K per unit in production.

The GPX program aimed at increasing the ability of GPS users to operate effectively in the presence of enemy jammers or countermeasures. The Program provided enabling technology that supports the development of high-altitude, unmanned aerial vehicle (UAV)-based GPS pseudolites. Airborne Pseudolites (APLs) are rapidly deployed GPS Navigation Warfare assets that provide theater-wide coverage to combat the effect of GPS jamming ranging from the individual soldier to combat platforms and precision GPS-guided shoot-to-coordinate weapons (e.g., JDAM, JSOW, TLAM, SLAM-ER, AGM-130, etc.). The considerably increased transmit power of the APL fights off the effects of jamming on the DoD receivers. In this approach, the NavWar resources are concentrated on the APLs instead of having to be deployed to each DoD GPS receiver.

APLs must overcome the following two critical challenges: (1) Backward compatibility - solves the non-Keplerian motion of the UAV platform in a manner that accommodates APL use with a software-only modification to existing DoD GPS receivers (e.g., PLGR, JDAM, etc.); and (2) APL self-positioning - provides sufficiently high GPS jam resistance on the APL to continue precision self-positioning using the GPS satellites directly through jamming. DARPA's GPX consist of a two-pronged effort leading up to flight demonstrations of brassboard equipment. The first demonstration is an APL broadcast signal to existing DoD GPS receivers. The second demonstration will be of an advanced digital adaptively beam-formed GPS anti-jam array antenna.

On December 18, 1996, the Defense Advanced Research Projects Agency (DARPA) Tactical Technology Office (TTO) and the Naval Air Systems Command (NAVAIR) Air Combat Electronics Program Office (PMA-209) announced the successful completion of a joint flight demonstration of an advanced navigation set on an F/A-18. Personnel from the Naval Air Warfare Center, Aircraft Division (NAWCAD), Patuxant River, Md., provided engineering and integration of the navigation set into the aircraft. They also provided the aircraft itself and the ground and flight crews. Flight testing was conducted Nov. 26 - Dec. 17, 1996.

DARPA provided a Phase 1 Global Positioning System (GPS) Guidance Package (GGP) for the tests. The GGP consists of a miniature inertial navigation set (INS), a 10-channel receiver capable of processing GPS precision position service signals and a navigation computer. The GPS receiver and INS are tightly coupled, which allows them to aid each other, depending on GPS signal conditions and the air alignment mode. The objectives of the flight demonstrations were threefold: to demonstrate GGP performance under highly dynamic conditions (e.g., 7.5g acceleration); to demonstrate the advantages of a tightly coupled architecture; and to demonstrate various modes of operation. The modes include blended GPS/INS navigation; inertial-only navigation, simulated periodic jam-out of GPS signals and inflight alignment of the INS.

For the tests, the GGP was mounted in the nose of the F/A-18 and a single GPS antenna was mounted on the top of the aircraft. Instrumentation included data recording equipment and a differential GPS reference receiver for ground truth. Recorded data enabled the calculation of GGP performance in position, velocity, and GPS satellite tracking.

Prominent among the flight profiles were a diamond pattern and simulated bombing and combat maneuvers, e.g., air-to-air combat. The diamond profile had relatively long legs and tested both blended GPS/INS and INS-only navigation. The bombing and combat maneuvers included up to 7.5g turns and rapid changes in altitude and airspeed. Barrel rolls, Immelmans and split maneuvers were included in some flights. This took the top-mounted GPS antenna out of line-of-sight to GPS satellites. The high value of tightly coupled INS aiding was thus demonstrated. The INS navigated when the GPS receiver had no signals, and enabled reacquisition of GPS signals within seconds once the aircraft rolled level.

GGP Phase 1 was developed under DARPA sponsorship by Litton Industries, Woodland Hills, Calif., and Rockwell International Collins Avionics and Communications Division, Cedar Rapids, Iowa. Following this, the program entered in its second phase, during which navigation performance will be increased, and size, weight and power will be significantly reduced. Litton Industries and Honeywell Inc. are leading the teams competing in the Phase 2 development phase.

DAMASK

The DAMASK unit is a simple, fully strapdown (no gimbals) seeker with only 12 parts which can be inexpensively assembled from commercially available off-the-shelf components. Designed to increase the accuracy of a standoff weapon, the DAMASK add-on kit also provides an additional piece of insurance for GPS INS guided weapons by circumventing the effects of GPS jamming. In future tactical situations, U.S. strike pilots may well have to launch weapons against enemy sites that are protected by GPS jamming. Military planners take such jamming very seriously because it can dramatically reduce the accuracy of precision guided weapons.

The DAMASK program was a 3-year Fleet Advanced Technology Demonstration (ATD), begun in response to the Navy's need for a low-cost, direct-attack weapon with 3-meter accuracy. With the successful flight of GR-2, the development program reached its conclusion.

JDAM's INS, when coupled for example with GPS updates throughout the weapon's flight, can achieve an accuracy of 13-meters circular area of probability (50 percent of the rounds impact within 13 meters of the target, 50 percent outside that radius).

With DAMASK, the GPS-INS accuracy increases to three meters, as was demonstrated in the DAMASK guided flight, GR-1. But with GPS denied, and INS alone guiding the weapon, accuracy drops to 30 meters. The GR-2 test was designed to duplicate the GPS-jamming scenario and measure the effect DAMASK would have in tightening that 30-meter accuracy.

During the DAMASK GR-2 test, a JDAM was released from an F-16 at a slant range of about 6 miles, altitude of 28,000 feet MSL, and speed of 0.8 Mach. From the point of launch, the JDAM received no GPS signals, navigating solely on INS. About 1,800 meters from the target, the DAMASK signal processor compared the target area view through the IR seeker with a target-area template that had been loaded before flight, and then sent a correctional signal to the JDAM's tail-control surfaces. Five seconds later the weapon punched through the target plate.

DAMASK's sub 3-meter accuracy in the first guided round test, GR-1, demonstrated that the program had met its design goal. GR-2 reinforced that demonstration with even greater accuracy under more difficult conditions. The improvement in accuracy was due in part to refinements in the signal processing algorithms that were incorporated into DAMASK between GR-1 and GR-2. The DAMASK hardware was identical for both guided rounds. The program surpassed its goal of 3-meter accuracy in both of the guided-round tests.

DAMASK development was funded by the Office of Naval Research. The program benefited from ONR's investment in several earlier research programs, especially the Concurrently Engineered Seeker (a semi-strapdown seeker that incorporated parts made from heavy-duty, carbon-fiber-filled plastic). DAMASK has also benefited from work performed for the Air Weaponry Technology Program. As of 2000, DAMASK was one of several candidate systems for the JDAM Product Improvement Program, which was then slated to begin in 2002.

JDAM GPS SAASM and GPS Anti-Jam

On 15 November 1998, the Joint Chiefs of Staff released SAASM instructions detailing that as of 1 October 2002, procurements of non-SAASM GPS user equipment would be disallowed. Plans were made to contract JDAM Global Position System (GPS) receiver upgrades to comply with new security requirements and GPS signal denial threats.

The scope of this effort was to design and test an upgraded GPS receiver compliant with Selective Availability Anti-Spoofing Module (SAASM) security protocol and the addition of added signal acquisition capability in a jammed environment.

JDAM GPS Selective Availability Anti-Spoofing Module (SAASM) integration and anti-jam integration efforts were scheduled to begin in FY03.



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Page last modified: 07-07-2011 02:51:34 ZULU