If the challenging technology can be developed as planned, the YAL-1A Airborne Laser will become USAF’s first operational airborne laser weapon. Plans call for the ABL to take its first realistic test shot at the end of 2008. The ABL is, essentially, a 747-type cargo aircraft equipped with a powerful chemical laser weapon, primed for shooting down ballistic missiles in their boost phase.
The ABL, however, probably will mark just the start of a broader laser era. Service officials believe the combat potential of lasers—for offensive and defensive weapons, protective systems, sensors, and myriad other military applications—goes well beyond the multibillion-dollar ABL program itself. (See “Attack at the Speed of Light,” December 2002, p. 26.)
The massive megawatt-class laser crammed into the ABL takes up every inch of space in the 747. However, the Air Force has begun preparing for the day when much smaller “kilowatt-class” lasers can be fitted into smaller aircraft. Although no such program is now funded, service officials are enthusiastic about the capabilities that would flow from a 100-kilowatt laser mounted into an F-35 fighter, for example.
Those capabilities include attack at light speed, dead-on accuracies, and uncompromised lethality, according to Col. Gail Wojtowicz, chief of the Future Concepts and Transformation Division in the Office of the Deputy Chief of Staff for Plans and Programs.
The laser beam can reach a target 23 miles away instantly. An AIM-120 air-combat missile, on the other hand, would take more than 30 seconds to reach a target at the same distance.
Lasers also would be significantly more accurate than even the most precise laser guided bombs. The laser’s circular error probable—the radius of a circle within which 50 percent of all of the target shots would fall—is less than an inch, according to Wojtowicz.
Finally, lasers are not explosive, even though the heat they generate can have destructive effects.
An ABL beam that is aimed for just two seconds at a ballistic missile or fuel tank, for example, would have about the same effect as one pound of high explosives on those targets. At the same time, because the heat energy lasers generate can (theoretically) be adjusted, they could be more flexibly employed. There are “lots of different dimensions for how ... we would use this in the future,” said Wojtowicz.
Master PlanTo prepare, the future concepts division recently completed work on an Air Force directed energy master plan that examines how lasers and other directed energy technologies could be integrated with Air Force platforms. The master plan was ordered after a 2004 wargame demonstrated the battlefield potential of a number of directed energy capabilities, said Wojtowicz. Potential directed energy capabilities, including lasers, were a focus in the follow-on Future Capabilities Assessment ’05 wargame, held last October.
The directed energy master plan has helped Air Force officials identify at least six directed energy programs that might be accelerated to develop promising technologies sooner.
Among those are three laser-related programs. Although service officials declined to name specific programs, they did give examples of the kinds of capabilities they are most interested in. Officials express interest in laser-equipped F-35 Joint Strike Fighters; lasers aboard gunships; and “relay mirrors” to increase laser ranges.
One laser capability service officials are eyeing for acceleration is a 100-kilowatt solid-state laser on a combat aircraft, said Wojtowicz. Although no funding has yet gone into putting such a laser on a fighter, a “sample S&T roadmap” document estimates that the Air Force may have to make a procurement decision in 2016. Solid-state laser technology could be sufficiently mature by then to begin buying a laser-equipped F-35.
Funding for integrating the laser on the F-35 would have to be provided before that date if laser technology continues to mature as expected.
“The integration [with] the airframe is the challenge. ... Anytime you go and change an airframe, the spiral on the airframe itself gets pretty expensive,” said Wojtowicz. “But again, the warfighter should try to keep that in mind as the development of the JSF goes along.”
It is already too late in the F-22A program, for example, to consider adding a laser weapon and the associated power, beam control, and subsystems. The structural modifications would be prohibitively costly.
However, a design characteristic of one version of the F-35 could make the future integration of a laser on the joint fighter much easier, said Howard Meyer of the Air Staff’s operational capability requirements electronic warfare division. Removing the lift fan from the short takeoff, vertical-landing version of the F-35 would provide “a tremendous amount of room” to house the components of a laser system, Meyer said.
Laser Gunships?Another capability the Air Force would like to see developed quickly is an aircraft-mounted tactical laser. Since 2001, US Special Operations Command has sponsored an Advanced Tactical Laser concept demonstration. Such a system, if it proved out, could eventually be mounted on an AC-130 Gunship for use against ground targets.
The Advanced Tactical Laser program has so far focused on using a chemical oxygen-iodine laser (COIL) similar to that which is being developed for the ABL. However, the Air Force also is watching closely the progress of a 25-kilowatt solid-state tactical laser test bed funded by the Air Force Research Laboratory and DOD.
Both Raytheon and Northrop Grumman have recently demonstrated 25-kilowatt solid-state lasers using the test bed, according to Roy Hamil of AFRL’s Directed Energy Directorate in Albuquerque, N.M. Two teams have been selected to participate in a follow-on 100-kilowatt solid-state laser test bed, Meyer said.
In a final laser-related program, the Air Force is considering a relay mirror that could be mounted on an airship or other “near-space” platform, to extend the range of laser beams to more effective ranges.
Many are skeptical that such technology is feasible, Wojtowicz said, but benefits would be substantial.
Such a system would allow laser-equipped aircraft to stand off farther from potential targets.
Relay mirrors also could preserve laser beam quality, which is degraded by atmospheric disturbances. A relay mirror would be high in the atmosphere, so a laser’s path from its source to the mirror and then to a target would be through thinner air, reducing degradation. In addition, a relay mirror could be equipped with an “optics bench” to clean up laser beams and make them “pristine” for the duration of their route to a target, Meyer said.
The development of such a capability depends in part on host platforms, such as the High Altitude Airship advanced concept technology demonstration and other fledgling near-space projects.
Developing a deployable solid-state 100-kilowatt laser is the informal goal of much of the science and technology development that AFRL is now undertaking or sponsoring.
Solids Vs. ChemicalsChemical lasers are able to achieve much greater power than solid-state lasers, as the ABL’s megawatt-class COIL demonstrates. However, because they are powered by large volumes of toxic chemicals, they present obvious logistical problems.
ABL, for example, is powered by six SUV-sized chemical “batteries” that must be housed in the back of the 747. Solid-state lasers, however, are powered by electricity, which is used to produce energy that is passed through a variety of solid media—usually crystal or a glass compound—to produce a laser. On an aircraft, electricity for powering a solid-state laser can be generated by burning jet fuel.
In addition to being lighter, the fact that they are electric means that solid-state lasers have a “deep-magazine,” requiring only aircraft refueling in order to rearm.
However, there are two primary problems that solid-state lasers pose: efficiency and thermal management. Most current solid-state lasers are 10 to 20 percent efficient. To produce a 100-kilowatt laser beam, for example, between 500 kilowatts and a megawatt of electricity must be produced.
This inefficiency leads to another problem—getting rid of the excess heat generated by the electricity that does not go toward powering the laser. In the case of a 10 percent efficient 100-kilowatt laser, 900 kilowatts of electricity are wasted. If the heat is not dispersed, it will be absorbed by the laser medium and cause beam distortion.
“Any sort of nonuniform deposition of heat in the medium results in distortion, [which] degrades the laser beam so it’s not really useful for focusing on a target at long distances,” Hamil said.
For this reason, much of AFRL’s solid-state laser research is focused on improving efficiency. “If we find something that’s more efficient, it pays great dividends,” he said, because you have to generate less power and there is less “thermal residue, which shows up in the worst places, right in your medium, which distorts the beam.”
AFRL and private researchers are exploring a number of solutions to the problem.
Fiber optic lasers are among the most promising potential solutions. Such lasers use glass fibers rather than traditional solid-state media and recently have demonstrated efficiencies in excess of 30 percent, according to Hamil. In addition, a single fiber has been shown capable of producing laser output radiation in excess of two kilowatts.
The main problem with fiber optic lasers is that grouping together several fibers to produce a powerful weapons-caliber laser—50 fibers to produce a 100-kilowatt laser, for example—has proved difficult.
“Locking those together is no small feat,” Hamil said. “It requires very sophisticated sensing and control of these fibers to be able to match each one of the phases so they look like one single aperture.” Despite this, AFRL has “great hopes” for fiber lasers as the answer to the efficiency and thermal management quandaries, Hamil said.
Yet another technological obstacle to the near-term deployment of laser weapons is beam control—ensuring a laser beam maintains its strength and quality as it shoots through the atmosphere. There are a number of optical approaches to beam control. The ABL program, for example, uses an atmospheric compensation system consisting of a tracking laser and a computer-controlled bendable mirror. The tracking laser gauges atmospheric conditions and the mirror predistorts the laser before it leaves the aircraft.
The laser is adjusted thousands of times a second, and the atmosphere then acts to focus the laser onto the target.
No Simple AnswerAFRL also has experimented with “beam conjugation,” which involves reflecting a beam that already has been distorted by the atmosphere back on itself. The resulting beam is “180 degrees out of phase” with the original beam, and the atmosphere serves to focus it perfectly, Hamil said.
The bottom line is that there is no simple solution to guarantee beam control. Though AFRL is making progress on all technological fronts, Hamil predicts it will be at least 10 years “and probably 20 years” before solid-state laser weapons are flying around, usable in combat.
Military utility of lasers extends well beyond kinetic weapons. Uses range from defensive systems for countering man-portable anti-aircraft weapons, to nonlethal crowd-control devices, to sensor systems that use lasers to detect enemy weapons or infrastructure through foliage or other concealment. The directed energy master plan looks at all such potential uses for lasers.
The Air Force is particularly intrigued by the possibility of fielding nonlethal lasers and directed energy capabilities. If USAF had access to “dial-a-yield” weapons or directed energy weapons with temporary or reversible effects, the range of capabilities the service could offer to the national command authority would be greatly expanded, said service officials.
“I would suggest to you that in the long term, 15 years plus, directed energy [will have] the greatest transformational effect on how we fight wars,” Wojtowicz said.
While Wojtowicz’s office is attempting to see what the future holds for directed energy, the service’s Directed Energy Task Force is making sure the Air Force is preparing for that future. Headed by Maj. Gen. Stanley Gorenc, director of operational capability requirements, the task force is looking across all Air Force functions—doctrine, organization, training, materiel, leadership, personnel, and facilities—to make sure directed energy is being considered.
This includes everything from ensuring that eye-protection against laser weapons is institutionalized in service training and operations, to examining legal issues relating to the use of directed energy weapons.
Defenses against directed energy capabilities are a special concern of the task force, because US enemies are known to be pursuing such technology. That’s one reason the Air Force Secretary and Chief of Staff decided to establish the task force, even before requirements for DE-related capabilities existed in many cases.
“In this case, our leadership had the foresight to understand that this was on the horizon,” said Col. Mike Edwards of the Directed Energy Task Force. Planning now against enemy use of directed energy can mitigate the threat and “allow protection of people first, then assets, then capabilities.”
The task force has at least a two-star general or senior executive service participant from each headquarters directorate, each major command, and each direct reporting unit. Major commands such as Air Force Materiel Command whose responsibilities relate very heavily to directed energy may have more than one member.
In May 2005, as a result of the task force’s work, then-Chief of Staff Gen. John P. Jumper signed out 75 “taskers,” assigning offices of primary responsibility and requesting further feedback for various directed energy issues, according to Edwards.
If the Air Force performs an analysis of alternatives for a specific requirement, the task force wants to ensure that directed energy alternatives are considered. In other cases, the task force is looking at field-testing promising directed energy technologies.
For example, a “ground-based laser test emitter” called LAZARUS is now being used to test various defenses against lasers. Until directed energy considerations are “fully institutionalized, the task force will stay around,” Edwards said.
In the meantime, the advancement of the state of the art in laser capabilities continues. ABL, the most advanced laser weapons program in the Defense Department, is progressing toward a planned shootdown of a missile in flight, scheduled for 2008.
Officials are keeping close watch on its development. In March, Lt. Gen. Henry A. Obering III, Missile Defense Agency director, said if ABL proves to be prohibitively expensive or unsupportable in a combat environment, it will not be pursued.
Last December, the program completed a major milestone, lighting its megawatt-class laser (the specific power of the weapon is classified) for more than 10 seconds in a lab at Edwards AFB, Calif.
The ABL program’s 747 is now being modified in Wichita, Kan., for installation of the laser. The program had a “very successful year” in 2005, said program director Col. John A. Daniels.
The ABL is a technology “pathfinder,” and success would bode well for future directed energy systems. Operational weapons may still be years away, but the future of laser and directed energy technology looks promising.
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