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The Airborne Laser: Boost-Phase Missile Defense at the Speed of Light
James B. Thordahl
The Aerospace Corporation has worked alongside contractors and government personnel to develop the Airborne Laser—one of the first lines of defense in the Ballistic Missile Defense System.
The Airborne Laser (ABL) is the world's first airborne platform designed to autonomously detect, track, and destroy hostile ballistic missiles during their vulnerable boost phase of flight. As the air-based component of the Ballistic Missile Defense System (BMDS), the Airborne Laser's primary mission is to protect the United States, its deployed forces, friends, and allies from a ballistic missile attack. It consists of a megawatt-class chemical oxygen-iodine laser integrated with a beam-control/fire-control system and a battle management, command, and control system on a highly modified Boeing 747-400 freighter aircraft.
The ABL program office is located at Kirtland Air Force Base, New Mexico, where the demonstration goal of shooting down a boosting missile has taken giant strides between 2004 and 2007. Successful milestones include complete installation and ground testing of the laser in a 747 integration lab, airborne testing of the passive acquisition and tracking systems, and ground and flight tests of the active mission payload, which include ABL's kilowatt-class track and beacon illuminators and a low-power surrogate laser. These latest tests demonstrated ABL's complete engagement sequence against a noncooperative airborne target, including passive acquisition, active tracking, target ranging, pointing, and atmospheric compensation. A dual-path approach of high-power testing of the laser system on the ground and low-power testing of the integrated beam-control and battle-management segments on the aircraft allows parallel progress and risk reduction in both areas prior to full system integration.
The concept of ABL developed through collaboration between the U.S. government and an industry team of Boeing, Lockheed Martin, and Northrop Grumman. Like many large acquisition programs, the ABL program office has relied on Aerospace to provide objective programmatic support and technical expertise throughout the acquisition, development, and execution phases of the process.
Aerospace's Role
Aerospace has been part of the ABL team since the program's inception in 1996. Five Aerospace engineers provide continual support in the areas of integration and testing, systems engineering, software acquisition and engineering, and the overall integration of the ABL into the BMDS.
This small Aerospace team has made a large impact on the program by providing onsite technical and programmatic reviews during key ground and flight test phases, by serving as the government's technical advisor for development and integration, and by acting as the primary ABL interface to the Missile Defense Agency (MDA) for integration into the BMDS.
ABL uses its megawatt-class laser to heat the skin of a target missile during its boost phase. Combined with the powerful stresses of launch, the laser spot causes a critical breach that essentially rips the missile open. Debris from the missile is more likely to fall near the launch site, rather than the missile's intended target. |
Aerospace has been recognized for its contributions: the team was thrice named ABL technical contractor of the year, it received the Air Force Materiel Command Test and Evaluation Award, and it has been placed on the MDA's contractor honor roll.
Mission and Concept of Operations
ABL was originally conceived as a theater weapon that would be used by the United States to target ballistic missiles in a combat theater, such as the Scuds used by Iraq during Desert Storm. However, under the MDA, ABL has become part of a layered defense system. Its mission is no longer only to shoot down theater missiles, but to shoot down any missiles that may be attacking friendly troops or nations. As an integrated element of the BMDS, ABL can also provide early launch warning, launch-point and impact-point prediction, and target cueing to other elements of the BMDS.
The future concept of operations includes a squadron of seven Airborne Lasers stationed in the United States, deployable worldwide and combat ready within 24 hours. In a wartime scenario, ABL would stand off from the border of a hostile territory outside the range of surface-to-air missiles, loiter at approximately 40,000 feet, and fly a figure-eight combat air patrol while constantly scanning for the infrared signature of a ballistic missile. It would be supported by fighter aircraft and refueled in flight to provide upwards of 12 hours on-station per aircraft. The weapon system will have a range on the order of hundreds of kilometers.
ABL is designed to engage targets in their boost phase shortly after launch. A missile is under tremendous forces when it is first launched, and ABL will use this to its advantage by heating up the skin of the missile with its laser, causing the missile to essentially rip itself open. Since the engagement would occur shortly after launch, debris from the missile would most likely fall near the launch site, rather than near the missile's intended target (see sidebar, The Engagement Sequence ).
System Description
There are four major components to the ABL system: the aircraft, the battle-management system, the beam-control/fire-control system, and the laser system. The aircraft is a commercial Boeing 747-400 freighter. Significant modifications were made to it when it was purchased off the assembly line, including removal of the nose to allow for installation of the turret and its 1.5 meter telescope, reinforcement of the floor to accommodate the load of the laser, and replacement of the bottom skin of the aircraft with a titanium belly to withstand the heat of the laser's exhaust.
The ABL is comprised of a battle management system, a sophisticated beam-control/fire-control system and a megawatt-class chemical oxygen-iodine laser all integrated in a highly modified Boeing 747. |
The battle-management system acts as the weapon system controller and provides autonomous target acquisition that allows ABL to acquire missiles within the tight boost-phase timelines. The communications equipment—mostly off-the-shelf—shares information for joint operations with other elements in the BMDS as well as the Command and Control, Battle Management, and Communications (C2BMC) system, giving the warfighting commander real-time information about missile launch and defense. ABL's battle-management segment also performs mission planning and serves as the operator interface via consoles and displays.
The beam-control/fire-control system makes critical adjustments to the laser beam so that it can transmit its energy onto the missile in a focused spot to ensure lethality. This system passively acquires the missile using the infrared signature of the plume, actively tracks the missile to stabilize the target in the laser-beam train, minimizes pointing jitter, and compensates for atmospheric effects. Atmospheric compensation is key to accurately transmitting the laser beam over the long distances crucial to the warfighters' needs. A major challenge of the beam-control/fire-control system was its optics. There are more than 100 optical components in the system ranging in size from 2.5 to 170 centimeters, each requiring a unique optical coating. To simultaneously point the outgoing lasers, measure returns from the target, and ensure maximum power on target, some optics need to be perfectly reflective, others perfectly transmissive, and still others must transmit or reflect only very specific wavelengths.
The laser system uses chemical oxygen-iodine laser technology that relies on the interaction of basic hydrogen peroxide and chlorine to create excited oxygen. Once this compound is injected with iodine, it creates photons. To generate "lethal" power, the system employs six laser modules that are each roughly the size of a Mini Cooper standing on end, and two large optical benches that form the laser resonator. Advanced fabrication and weight-reduction technologies have helped create a megawatt-class laser system that can be installed on a commercial aircraft.
Dual-Path Testing
The ABL program has been structured to enable dual-path development and testing. One path is used for integration and high-power testing of the laser in a systems integration laboratory on the ground. The other allows for concurrent low-power ground and flight testing of the mission payload, including the battle-management and beam-control/fire-control systems.
ABL is structured for dual path development. This includes high-power testing of the chemical oxygen-iodine laser device and low-power ground and flight testing of the mission payload. Both low-power and high-power testing are complete and the two paths have converged into weapon system integration and test. |
These tests are "low power" because the full-scale laser is not yet installed on the aircraft. When it completes its systems-integration laboratory tests, along with flight tests of the low-power mission payload, the laser will be installed on the aircraft, and system-level high-power ground and flight tests will be conducted. This will conclude with a demonstration of the system's lethality by shooting down a ballistic missile.
Recent Accomplishments
The ABL program has been developing incrementally along key events or "knowledge points." This assessment approach involves preplanned events that represent a time where critical knowledge is gained and can be used by decision makers to confirm the ABL's viability. Knowledge points for the ABL have progressed through increasing degrees of integration and testing and reflect significant levels of accumulated understanding.
A surplus 747 fuselage known as the Systems Integration Laboratory was used as the platform to integrate and initially test the laser system. The image shows the six laser modules and one of the optics benches prior to removal and installation on the aircraft. |
Successful knowledge points between 2004 and 2007 include the first light of the integrated high-energy laser system; the first flight of the passive mission payload, which is comprised of the battle-management and beam-control/fire-control systems; flight testing of the passive mission payload; lethal-power and full-duration ground testing of the high-energy laser system; integration of the track and beacon illuminator lasers and testing of the active mission payload; flight testing of the active payload and engagement of a noncooperative airborne target; and readying the aircraft and support systems for high-power systems integration.
Low-Power Flight Test
A recent accomplishment—and arguably the most significant to date—was the low-power active flight-test series. This included a demonstration of ABL's key engagement functions, including passive and active tracking, atmospheric compensation, and pointing of a surrogate laser against an airborne target.
The target, a KC-135 aerial refueling aircraft named Big Crow, was modified to support the testing. A missile silhouette was painted on the side of the aircraft, and a bank of heat lamps were installed at the rear of the "missile" to emulate its plume. Cameras were also installed on the wing tip to look back at the silhouette and provide scoring of the three laser beams, including beam size, jitter, and irradiance. The ABL flew 55 missions against Big Crow over nine months, incrementally demonstrating the individual portions of the engagement sequence at operationally representative ranges and substantiating weapon systems performance, including atmospheric and local wavefront compensation.
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Top: The Airborne Laser with the target aircraft Big Crow, a modified KC-135 aerial refueling plane. Left: Sensor images of the surrogate high-energy laser on Big Crow with atmospheric wavefront compensation closed and local wavefront compensation open (far left) and both loops closed (middle). |
This focusing or correction of the laser represents the endgame for ABL—to get to this point, the battle-management system had to detect the target, pass its coordinates to the beam-control/fire-control system (which in turn had to slew the turret assembly), acquire the plume in its acquisition sensor, and hand off to the plume tracker. The track illuminator laser was propagated and walked to the nose of the target, its return was sensed and used to actively track the target. The beacon illuminator laser was propagated, and its return was used for atmospheric compensation. Finally, the surrogate high-energy laser was propagated and accurately pointed to the desired location on the target.
The performance measured during low-power systems integration offered confidence that the system has the necessary lethality to move into the next phase: high-power systems integration.
Path Forward
The first ABL is housed in a hangar at Edwards Air Force Base undergoing laser system installation. Once the installation is complete, the system will go through a series of activation and ground tests.
Incremental testing of the laser will include first light of the laser into a local calorimeter followed by propagation through the beam-control/fire-control optical system. This ground testing is facilitated by an extensive set of support equipment, including a ground pressure recovery system that allows for testing at pressures similar to what the laser will experience in flight. The tests will also be conducted with a range-simulator diagnostic system that catches and measures outgoing laser beams and provides laser returns. These returns simulate the returns of the track and beacon illuminator lasers off a target. This allows the engagement sequence to be simulated on the ground without an actual target.
The ground pressure recovery system vacuum sphere allows testing of the high-energy laser on the ground. |
Following verification of system-level functionality and characterization of ground performance, ABL will return to the air in its quest to shoot down a ballistic missile. Flight testing will commence with regression tests against an airborne diagnostic target similar to Big Crow followed by a series of engagements against dynamically representative targets. The targets include Terrier Lynx rockets as well as instrumented vehicles referred to as missile alternative range target instruments. These Black Brant rockets include sensor payloads from MIT's Lincoln Laboratories that measure the track illuminator, beacon illuminator, and high-energy laser wavelengths. This phase of testing is scheduled to culminate in late 2009 with a lethal demonstration—negation of an actual ballistic missile during its boost phase in a representative scenario.
Summary
ABL is a revolutionary system that takes directed energy from the laboratory to the battlefield and provides the first line of defense against a ballistic missile attack. Tremendous progress has been made over the past several years, and all of the building blocks of the system have come together through successful testing, including full-power, full-duration lasing from the six-module high-energy laser and completion of flight testing of the aircraft with all beam-control systems installed. These successes allowed the program to move into system-level integration and test and continue its march toward lethal system demonstration—that is, shooting down a real missile in flight.
