Laser Guided Bombs

Laser & Satellite guided strikers

LASER-GUIDED BOMBS Operating principle:

Laser-guided bombs have an internal semi-active guidance system that detects laser energy and guides the weapon to the target illuminated by an external laser designator.

Laser designators radiate a narrow beam of pulsed energy in the near infrared wavelength spectrum. These are semi active illuminators used to tag the desired spot. These can be aimed such that laser energy precisely designates the chosen spot on the target. Laser designator can be located in the delivery aircraft, another aircraft or on a ground source.

Typical LGB seekers comprise an array of photo diodes to decode the laser pulsed repetition frequency (PRF) and derive target position signals. Laser designators and seekers use a pulse coding system to ensure that a specific seeker and designator combination work in harmony. By setting the same code in both the designator and the seeker will track only the target designated by the chosen designator.

Laser & Satellite guided strikers Laser designators provide precision target marking for air support. LGBs with TV or infrared seeker in their nose show the target to the attacking pilot on a screen in the cockpit. The pilot fixes cross hairs on the target and marks it for the weapon to aim at. The target scatters the received laser energy in all the directions. LGB seeker having a limited field of view receives a small part of the scattered energy and decodes it. If the received PRF code matches the preprogrammed code, the pilot fires the bomb. It then horns onto the reflected laser energy to attack the target

Some LGBs require laser target illumination before launch or release and/ or during the terminal portion of flight. The LGB flight path can be divided into three phases: ballistic, transition, and terminal guidance.

During the ballistic phase, the weapon continues on the unguided trajectory established by the flight path of the delivery aircraft at the moment of release. In this phase, the delivery altitude takes on additional importance, since maneuverability of the unguided bomb is related to the weapon velocity during terminal guidance. Therefore, airspeed lost during the ballistic phase equated to a proportional loss of maneuverability. So the closer to the target the release of the bomb, the more the accuracy of the bomb

The transition phase is where initial acquisition of the designating laser takes place. During this phase, the weapon attempts to align its velocity vector with the line of sight vector to the target. Once a lock has been achieved, the guidance system uses the canards to try and keep the bomb within the cone of the reflected laser energy.

The terminal phase is when the reflected laser centers on the seeker causing the bomb to dive to the target. LGBs are excellent performers in dive deliveries initiated from medium altitude. A steep, fast dive attack increases LGB maneuvering potential and flight ability. Medium-altitude attacks generally reduce target acquisition problems and more readily allow for target designation by either ground or airborne designation platforms. Medium-altitude LGB dive delivery tactics are normally used in areas of low to medium threat.

LGBs miss the target if the laser is turned on too early: During certain delivery profiles where the LGB sees laser energy as soon as it is released, it can turn from its

Laser & Satellite guided strikers delivery profile too soon and miss by failing short of the target. To prevent this, the laser designator must be turned on at the time that will preclude the bomb from turning down toward the target prematurely. Normally, the pilot knows the proper moment for laser ‘on’. The specific LGB and the delivery tactics of the attacking aircraft dictate the minimum designation time required to guide the weapon to the intended target.

The four basic requirements for effective use of laser designators with LGBs are: 1. The PRF code of the laser designator and the LGB must be compatible 2. A direction of attack must be determined because the LGB must be able to sense sufficient laser energy reflecting from the target being designated. 3. The laser designator must designate the target at the correct time. 4. The delivery system must release the weapon within the specific weapon’s delivery envelope.

Significance of PRF coding: The pulse coding system ensures that only a specific designator and seeker combination works. It can be used effectively and securely with LGBs .LGB codes are set on the bombs before take off and cannot be changed in the air. Individual aircrafts may carry LGBs with different preset codes. Different preset codes allow for multiple aircraft attacks, multiple weapon release and a variation in codes for consecutive attacks.

Coding allows simultaneous attacks on multiple targets by a single aircraft, or flights of aircraft, dropping LGB set on different codes. This tactic may be employed when several high-priority targets need to be attacked expeditiously and can be designated simultaneously by the supported units. Selection of PRF code can affect the target engagement success. A higher pulse rate gives the seeker the best opportunity to acquire the target in the time available; it is appropriate for the most important targets and the most difficult operating conditions.


Important modules of laser-guided bomb: The normal gravity bomb, often referred to as ‘Dumb-Bomb’, can be converted into a smart bomb by adding an LGB kit to it. The kit significantly improves the accuracy of the gravity bomb, there by reducing the collateral damage. Thus all LGB weapons essentially comprise the normal cavity bomb, computer group, guidance canards and a wing assembly.

The computer control group is mounted on the nose of the bomb and is the frontend guidance system. The computer section transmits directional command signals to the appropriate pairs of canards. The guidance canards are attached to each quadrant of the control unit to change the flight path of the weapon. The computer control group detects the laser-illuminated target, decodes the laser PRF and provides weapon guidance signals to the movable guidance fins. The canards reacts to the signals received from the computer control group to direct the weapon to the target.

The wing assembly is mounted on the aft end of the bomb body. It adds necessary aerodynamic and lifts for in-flight maneuvering. An electric fuse is installed in the tail of the bomb. LGBs are maneuverable, free fall weapons requiring no electronic interconnect to the aircraft.


COMMERCIALLY AVAILABLE LASER-GUIDED BOMBS 1. Paveway laser-guided bombs: Pave means precision avionics vectoring equipment. Three generations of paveway LGB technology exist, each representing a modification in the guidance mechanism: 1. Paveway 1: The guided-bomb unit (GBU) Paveway 1 LGBs had fixed wings. The front wings are called canards, while the rear ones are called wings. 2. Paveway 2: They have ‘pop-out’ wings, which makes handling and carriage easier. Other modifications include improved canards, upgraded sensor optics, reduced weight, reduced start up times and improved field of view. They were able to detect laser light emissions coded using the PRF technique. 3. Paveway 3: This is the latest version. The computer control group uses proportional guidance, which increases bomb range and accuracy.

Designation Guidance System Munition KMU-421/B SUU-54/b 2000-lb cluster bomb GBU-2 PAVEWAY I Mk 84 2000-lb bomb GBU-10 A/B KMU-351 A/B Mk 82 500-lb SNAKEYE GBU-12 A/B KMU-388 A/B KMU-420 /B Mk 20 Mod 2 ROCKEYE 500-lb bomb GBU-12 A/B M117 750-lb bomb GBU-12 A/B KMU-342 /B PAVEWAY II Mk 84 2000-lb bomb GBU-10 D/B KMU-351 E/B Mk 82 SNAKEYE 500-lb bomb GBU-12 C/B KMU-388 C/B Mk 83 1000-lb bomb GBU-16 C/B KMU-455 /B


2. Bombe a Guidage Laser: It features pop-out tailfins. 3. Griffin: It has been working on a new laser seeking system named the Advanced LaserGuided Bomb (ALGB) with improved accuracy, which appears to be the basis for a new LGB series called Lizard.


COMMERCIALLY AVAILABLE LASER DESIGNATION SYSTEM 1. Lantirn. Lockheed martin low-altitude navigation and targeting Infrared for night (Lantirn), is a pair of pods comprising the following: (a) The AN/AAQ-13 navigation pod, which includes FLIR and radar for terrain following and mapping, plus support computing and other electronics. (b) The AN\AAQ-14 targeting pod, with FLIR and a laser designator.

2. Litening. The unit comprises a pod containing 5 major sensors, a high resolution CCD, FLIR, laser illuminator, laser detector and a strap-down system.

3. TIALD. It is thermal imaging airborne laser designator. 4. PDLCT. Pod de Designation Laser a Camera Thermique, meaning laser designation pod with infrared camera

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LIMITATIONS OF LGBs Although LGBs are smart, precision weapons, these have some serious drawbacks. Smoke, dust and debris can impair the use of laser-guided munitions. The reflective scattering of laser light by smoke particles may present false targets. Rain, snow, fog and low clouds can prevent effective use of laser-guided munitions. Heavy precipitation can limit can limit the use of laser designators by affecting the line of sight. Snow on the ground can affect the accuracy of laser-guided munitions. Fog and low clouds block the laser guided munition seeker’s field of view, which reduces the guidance time. This in turn affects the probability of hit.

LGBs can miss the target if the laser is turned on too early there is also the problem of picking up the wrong target, by faults of maps or by sight recognition. Also the designator must project a laser spot steadily on the target for the final 10-30 seconds of flight at an angle that the weapons can see. LGBs have a limited off-axis capability; therefore precise attack planning is essential for laser mission accomplishment. Precise target marking with laser designators, is directly related to target size and aspect, laser beam divergence and designation angle.


JOINT DIRECTIVE ATTACK MUNITION

The precise work required by pilots in dropping LGBs sparked the development of other forms of guided weapons that do not require pilot’s guidance. Additionally, the weather limitations spawned a new breed of weapons that allow for accurate deployment in adverse weather conditions. Such weapons are guided using global positioning satellite (GPS) technology and are called Joint Direct Attack Munition (JDAM) bombs. These are one of the military’s chief solutions to the problem of laser guidance being affected by weather. Moreover, GPS is designed to be resilient to jamming effects.

Operation principle: JDAM is an add-on guidance kit attached to the tail of the normal gravity bomb to change it from a conventional weapon to a GPS-guided smart bomb.

GPS uses a constellation of 24 Navstar satellites that orbit the earth to provide accurate navigational signals. Each satellite orbits the earth to provide accurate navigational signals. Each satellite orbits the earth every 12 hours in a formation that ensures that every point on the planet is in radio contact with at least four satellites. Each Satellite continuously broadcasts a digital radio signal that includes both its own position and the time, exact to a billionth of a second. A GPS receiver compares its


own time with the time sent by a satellite and uses the difference between the two times to calculate its distance from the satellite. By checking its time against the time of three satellites whose positions are unknown, the receiver can pinpoint its longitude, latitude and altitude. For the system to work, the receiver has to know exactly where the satellites are and the satellites have to be able to keep accurate time, Accuracy is ensured by having each satellite carry four atomic clocks- the most accurate timing devices ever made. Thus by using satellite technology, GPS identifies both military and civilian user location anywhere on the earth and at any time within seconds. Potential target areas are mapped out ahead of time, identifying potential targets by their location (height above sea level. Latitude and longitude) With respect to the GPS system. When an attack raid is planned, the GPS guided weapon automatically begins its initialization process during captive carry when the aircraft applies power. It performs BIT and aligns its inertial navigation system, (INS) with the host aircraft’s system. Targeting data is automatically downloaded to the weapon from the host aircraft. When the host aircraft reaches the release point within the launch acceptable region (LAR), The weapon is released. Weapon maneuverability and range are enhanced by fixed aerodynamic surfaces (mid-body strakes) attached to the bomb body, once released, the bomb’s INS/GPS takes over and guides the bomb to its target regardless of weather. Guidance is accomplished via the tight coupling of an accurate GPS with a 3axiz INS


Important Modules of JDAM. The JDAM kit comprises a tail kit and a set of strakes that attach to 2000-pound MK-48 and BLU-109 warheads and 1000-pound MK-83 warheads. A fundamental model component that is common to all JDAM configurations is the guidance control unit (GCU). The GCU consists of the mission computer, inertial measurement unit (IMU), GPS receiver module (GPSRM) and the power supply. The IMU contains three ring laser gyros and accelerometers. The GPSRM consists of a 5channel P(Y)-code receiver with full selective availability/anti-spoofing capability. Autonomous launch-and-leave operation is achieved with the GPS-aided INS, an adaptive optimal guidance algorithm, an autopilot that features a robust servo structure and a tail actuator sub-system. The JDAM INS functions in unaided or GPS-aided navigation mode. INS-only is defined when GPS signal becomes unavailable, for example. GPS is jammed. In such a situation, The INS provides rate and acceleration measurements, which the weapon software develops into a navigation solution. This inherent capability counters the threat from near-term technological advances in GPS jamming. Four fins attached to the GCU provide for both flight control and lift. Stabilization and additional lift are provided by strakes attached to the sides of the bomb, By utilizing GPS/INS the weapon becomes fully autonomous once released and navigates to the designated target coordinates while being unaffected by weather or target conditions. The INS, with GPS updates, allows control fins to correct trajectory until the moment of impact. The target coordinates are sent to the bomb in two different ways. In preplanned targeting, all the target details including the desired bomb release envelope are uploaded to the aircraft before take-off. While in flight, the JDAM unit receives updates from the aircraft’s own INS/GPS. Allowing it to track its own position and compensate for alterations to the desired release window. When the pilot is within the predetermined release envelope, the bomb is released. The onboard GPS/INS then guides the weapon to the preset target coordinates. If for any reason GPS information is unavailable, the system will rely purely on Ins, which although not so accurate as GPS, keeps the bomb

Laser & Satellite guided strikers within an acceptable impact distance. The second method of delivery allows the pilot redesignate targets while in-flight.

Joint Direct Attack Munition (JDAM) GBU-29, GBU-30, GBU-31, GBU-32 The Joint Direct Attack Munition (JDAM) GBU-31 is a tailkit under development to meet both USAF and Navy needs, with the Air Force as the lead service. The program will produce a weapon with high accuracy, all-weather, autonomous, conventional bombing capability. JDAM will upgrade the existing inventory of general purpose and penetrator unitary bombs, and a product improvement may add a terminal seeker to improve accuracy. JDAM can be launched from approximately 15 miles from the target and each is independently targeted. JDAM is not intended to replace any existing weapon system; rather, it is to provide accurate delivery of general purpose bombs in adverse weather conditions. The JDAM will upgrade the existing inventory of Mk-83 1,000- and Mk-84 2,000-pound general purpose unitary bombs and the 2,000-pound hard target penetrator bomb by integrating a guidance kit consisting of an inertial navigation system/global positioning system guidance kit. The 1,000-pound variant of JDAM is designated the GBU-31, and the 2,000-pound version of the JDAM is designated the GBU-32. JDAM variants for the Mk-80 250-pound and Mk-81 500-pound bombs are designated GBU-29 and GBU-30, respectively. Hard Target penetrators being changed into low-cost JDAMs included the 2,000 pound BLU-109 and 1,000 pound BLU-110. Mission plans are loaded to the host aircraft prior to take off and include release envelope, target coordinates and weapon terminal parameters. The weapon automatically begins its initialization process during captive carry when power is applied by the aircraft. The weapon performs bit, and aligns its INS with the host aircraft’s system. Targeting data is automatically down loaded to the weapon from the host aircraft. When the host aircraft reaches the release point within the Launch Acceptable

Laser & Satellite guided strikers Region (LAR), the weapon is released. Weapon maneuverability and range are enhanced by fixed aerodynamic surfaces (mid-body strakes) attached to the bomb body. Once released, the bomb's INS/GPS will take over and guide the bomb to its target regardless of weather. Guidance is accomplished via the tight coupling of an accurate Global Positioning System (GPS) with a 3-axis Inertial Navigation System (INS). The Guidance Control Unit (GCU) provides accurate guidance in both GPS-aided INS modes of operation (13 meter (m) Circular Error Probable (CEP)) and INS-only modes of operation (30 m CEP). INS only is defined as GPS quality hand-off from the aircraft with GPS unavailable to the weapon (e.g. GPS jammed). In the event JDAM is unable to receive GPS signals after launch for any reason, jamming or otherwise, the INS will provide rate and acceleration measurements which the weapon software will develop into a navigation solution. The Guidance Control Unit provides accurate guidance in both GPS-aided INS modes of operation and INS-only modes of operation. This inherent JDAM capability will counter the threat from near-term technological advances in GPS jamming. The weapon system allows launch from very low to very high altitude and can be launched in a dive, toss, loft or in straight and level flight with an on-axis or off-axis delivery. JDAM also allows multiple target engagements on a single pass delivery. JDAM provides the user with a variety of targeting schemes, such as preplanned and inflight captive carriage retargeting. JDAM is being developed by Lockheed Martin and Boeing [McDonald Douglas]. In October 1995, the Air Force awarded a contract for EMD and for the first 4,635 JDAM kits at an average unit cost of $18,000, less than half the original $40,000 estimate. As a result of JDAM's pilot program status, low-rate initial production was accelerated nine months, to the latter half of FY 1997. On April 30, 1997, the Air Force announced the decision to initiate low-rate initial production (LRIP) of JDAM, with the first production lot of 937 JDAM kits. The JDAM Integrated Product Team achieved a phenomenal 53 guided JDAM weapon releases in the six months prior to the LRIP decision. JDAM demonstrated high reliability and outstanding accuracy. Twenty-two of the weapon releases were accomplished during an early Air Force operational assessment. Over a four-week period operational crews put JDAM through an operationally representative evaluation, including targets shrouded by clouds and obscured by snow. All 22 weapons successfully performed up to their operational requirements including overall accuracy of 10.3 meters, significantly better than the 13 meter requirement. Early operational

Laser & Satellite guided strikers capability JDAMs have been delivered to Whiteman Air Force Base, Mo., and low-rate, initial production JDAM deliveries begin on 02 May 1998. McDonnell Douglas Corporation of Berkeley, MO, was awarded on 02 April 1999, a $50,521,788 face value increase to a firm-fixed-price contract to provide for low rate initial production of 2,527 Joint Direct Attack Munition kits. The work is expected to be completed by January 2001. The JDAM program is nearing the end of its development phase. More than 250 flight tests involved five Air Force and Navy aircraft. JDAM will be carried on virtually all Air Force fighters and bombers, including the B-1, B-2, B-52, F-15E, F-16, F-22, F-117, and F/A-18. JDAM was certified as operational capable on the B-2 in July 1997. Limited Initial Operational Capability was achieved on the B-52 in December 1998. The B-1B Lancer conventional mission upgrade program is configuring the B-1B to carry out its role as the primary Air Force long-range heavy bomber for conventional warfare. The 11 Feb 1998 drop from a B-1B was the 122nd guided JDAM launch. The depot at Oklahoma City Air Logistics Center will install the modification kits in the initial block of bombers by January 1999, giving Air Combat Command seven JDAMcapable B-1B bombers 18 months ahead of the initial program schedule.

Potential Upgrades The JDAM product improvement program may add a terminal seeker for precision guidance and other system improvements to existing JDAMs to provide the Air Force with 3-meter precision and improved anti-jamming capability. The Air Force is evaluating several alternatives and estimates that the seeker could be available for operations by 2004. The seeker kit could be used by both the 2,000-pound blast fragmentation and penetrator JDAMs. The Advanced Unitary Penetrator (AUP), a candidate to be integrated with a GBU-31 guidance kit, is a 2000 lb. class penetrator warhead intended as an upgrade/replacement for the BLU-109 warhead in applications requiring increased penetration. The AUP is designed to provide increased penetration capability over the BLU-109 warhead while maintaining the same overall weight, mass properties, dimensions, and physical interfaces associated with the BLU-109 warhead. This concept integrates the AUP warhead with the GBU-31, the JDAM tail kit for 2,000 lb class warheads. This concept

Laser & Satellite guided strikers uses the Hard Target Smart Fuze (HTSF), an accelerometer based electronic fuze which allows control of the detonation point by layer counting, distance or time. The accelerometer senses G loads on the bomb due to deceleration as it penetrates through to the target. The fuze can distinguish between earth, concrete, rock and air. The boosted penetrator concept is based on achieving maximum penetration without sacrificing operational flexibility. Total system weight will be less than 2,250 pounds so that it can be carried by all AF tactical aircraft and bombers as well as the Navy’s F/A18. The goal is to achieve greater penetration than the GBU-28 with a near term, affordable design. A dense metal warhead will be used with a wraparound rocket motor to allow internal carriage in the F-117. Advanced explosives will be used to compensate for the reduced charge weight. This concept integrates the boosted penetrator warhead with a JDAM guidance kit with an adverse weather Synthetic Aperture Radar (SAR). The Ballasted Penetrator in GBU-32 concept is a 1000 pound dense or ballasted penetrator integrated with a GBU-32 guidance kit using compressed carriage for internal carriage in advanced fighters (F-22, JSF) or carriage in cruise missiles (JASSM, CALCM, ACM, ATACMS, Tomahawk.) The warhead would either be designed with a dense metal case or contain dense metal ballast for maximum penetration. The warhead will be filled with an advanced insensitive explosive to compensate for the reduced charge weight. The warhead will be integrated with the GBU-32, the JDAM tail kit for 1,000 lb class warheads. The Boosted Unitary Penetrator concept is based on achieving maximum penetration in a weapon that will fit internally in the F-22. Total system weight will be less than 1300 pounds. A dense metal warhead will be used with a wraparound rocket motor. Use of next generation compressed seekers and aero-control designs along with reaction jet control will allow the size to shrink sufficiently to fit inside F-22 and JSF. Advanced explosives will be used to compensate for the reduced charge weight. This concept integrates the boosted penetrator warhead with a JDAM guidance kit with an adverse weather Synthetic Aperture Radar (SAR). The JDAM/BLU-113 concept improves the GBU-28 by enhancing the nose design of the BLU-113 warhead for improved penetration. The warhead nose reshape will improve BLU-113 penetration by more than 25%. The penetration could potentially be further improved by replacing the traditional HE fill with a dense explosive. The design involves integrating the improved BLU-113 warhead with a JDAM tail kit.

Laser & Satellite guided strikers The Compressed Carriage GBU-32, J1K, enhanced fill concept is a JAST-1000 warhead with enhanced fill integrated with a GBU-32 guidance kit using compressed carriage for internal carriage in advanced fighters (F-22, JSF) or carriage in cruise missiles (JASSM, CALCM, ACM, ATACMS, Tomahawk.) The warhead is a combined penetrator and blast/fray warhead. The warhead shape is optimized for penetration and the enhanced fill `and internal liner provide blast and controlled fragmentation capability. The warhead is shrouded to match the MK-83 mass properties and interfaces. The warhead will be integrated with the GBU-32, the JDAM tail kit for 1,000 lb class warheads. Use of aerocontrol designs along with reaction jet control will allow the size to shrink sufficiently to fit inside F-22 and JSF. This concept uses the Hard Target Smart Fuze (HTSF).


Specifications

Mission

Close air support, interdiction, offensive counterair, suppression of enemy air defense, naval anti-surface warfare, amphibious strike

Targets

Mobile hard, mobile soft, fixed hard, fixed soft, maritime surface

Variant

JDAM

JDAM-PIP

Service

Air Force and Navy

Air Force

Program status

Development

First capability

1997

2004

Guidance method

GPS/INS (autonomous)

GPS/INS mid-course with a terminal seeker yet to be selected

Range

Greater than 5 nautical miles, up to 15 miles

Circular error probable

13 meters using integrated GPS/INS unit 3 meters 30 meters using INS only

Development cost

$683.9M FY 1995 estimate $399.3M FY 1999 estimate

Production cost

$4,154.4 million

Total cost

$4,650.6 million

Acquisition unit cost

$62,846

Average unit cost (40,000 units)

$18,000 current estimate $42,200 initial estimate

Quantity

Navy: 12,000 Air Force: 62,000

Air Force has programmed about $76.5 million for development through 2001

5,000--kits to be added to basic JDAM


LIMITATIONS OF JDAM BOMBS Although JDAMs are ten times more accurate than unguided bombs and ten times cheaper than LGBs, these are not foolproof either. If GPS guided weapon loses touch with the guiding satellite signals, it falls back on inertial navigation and calculates its position in relation to its last fixed position. In such a situation the inaccuracy of JDAM rises to about 30 metres. Since GPS-guided weapons aim at preprogrammed coordinates of the target. Coordinates of the target have to be precisely known.


CONCLUSION "In World War II it could take 9,000 bombs to hit a target the size of an aircraft shelter. In Vietnam, 300. Today we can do it with one laser-guided munition from an F-117." GPS-guided munitions are much safer and cheaper than laser guided bomb. These can be dropped from much higher altitudes, as against laser-guided bombs that require bomber crews to fly low enough to identify the target and illuminate it with a laser before dropping the bomb. GPS guided weapons are not affected by harsh weather conditions, nor do they leave the gunner vulnerable to attack.

As technology continues to advance, the face of warfare will continue to change. Efforts are on to improve the CEP of JDAM to 3 meters by adding the direct attack munition affordable seeker kit using cheap COTS components.


REFERENCES

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Howstuffworks How Smart Bombs Work.htm

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http://www.fas.org/man/dod-101/sys/smart/lgb.htm

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JDAM Public Page @ Eglin AFB

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JDAM @ Boeing

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Fundamentals of Lasers

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LASER RANGE SAFETY Range Commanders Council, White Sands Missile Range, OCTOBER 1998

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Acquisition Reform Success Story Joint Direct Attack Munition (JDAM)

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India today

Laser Guided Bombs

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