The first time that lasers accompanied US military forces into combat was in the Vietnam War, where they designated targets for laser-guided bombs. Since then, such devices have been used to determine distance to a target, to signal and communicate, and to disrupt optical devices of hostile forces.

The laser even has been used at times merely to frighten enemies; US troops can scare away "bad guys" by putting visible laser aiming "spots" on their chests at night.

In the next decade, however, lasers will take a dramatic step forward. No longer will they serve only as weapon enablers or as non-lethal systems. The lasers will themselves become hard-kill weapons. Megawatt-class devices will be put on the ground, in the air, and into space, where they will function as lightning-fast defensive systems.

"We can't even imagine" the ramifications of lasers as weapons, said Col. Michael W. Booen, director of USAF's Airborne Laser program. "It's tough to comprehend something that moves at the speed of light and what that means. We have a sense of the speed of ... airplanes or missiles but not the speed of light."

Of one thing, however, Booen is certain: Military lasers are destined to revolutionize airpower.

Laser weapons have long since departed the realm of the hypothetical. They are taking shape as real hardware, now, Booen said. The Airborne Laser is the nearest-term hard-kill laser weapon for the US military, and the Air Force ranks it just behind the F-22 air dominance fighter in its list of top equipment priorities.

The job of the ABL will be to orbit the skies near the forward edge of a battle area, watching with infrared search-and-track devices for the launch of enemy theater-range ballistic missiles. Once it spots one, the ABL platform--a militarized 747 freighter fitted with lasers for ranging, targeting, and attack--will get a lock on the target. When the missile rises above the clouds, the ABL will focus a beam of light 15 inches in diameter on the missile's skin. The skin will heat up and rupture, causing the volatile materials inside to explode. Debris--and the missile warhead--will rain down on the nation that launched it. This, it is thought, will serve as a deterrent to the use of theater ballistic missiles in the first place.

Blowback and Payback

As a bonus, the ABL will determine the launch location and then pass that information on to attack airplanes. This will help provide a missile-attack capability that is "better than anything we [have] now," Booen asserted. The strike aircraft can dash to the launch area and destroy other missiles on the ground before the enemy has a chance to fire them or move them to a new hiding place. The maturation of such capability will help plug one of the biggest gaps in US conventional power. In the Gulf War, for example, scores of unsuccessful Scud hunts for mobile missiles provided one of that conflict's most vexing problems.

"This is not a science project," Booen said. "This is an engineering project." All of the necessary ingredients to make the ABL work are now on the shelf. "Our job is to integrate these ... technologies."

The two toughest challenges for the ABL were generating a laser beam of sufficient power to destroy a missile in flight and keeping the beam coherent as it propagated through the turbulent atmosphere, which tends to distort light. Both problems have been solved. Now, the challenge is to make an operational system that is light enough to fly and hardy enough to last for years under a demanding deployment schedule.

The ABL's destructive element is the Chemical Oxygen-Iodine Laser. It works by combining fairly common chemicals--roughly comparable to household bleach and sink drain uncloggers--in a mixing chamber, creating energized oxygen. The energized oxygen generates photons--tiny particles of light--which are then shaped into a laser beam. The large quantity of chemicals can generate power in the multimegawatt range, Booen said. This power, when focused, is sufficient to heat the skin of a missile hundreds of miles away.

The other enabling technology is known as adaptive optics. On the ABL, a small laser will be pointed toward the target area. Backscatter of light from that laser will be analyzed to compute the turbulence in the atmosphere between the ABL and its target. These computations are translated to tiny pistons physically attached to the focusing mirror, which changes shape to cancel out the distortions and keep the attack beam focused.

In reverse, the technology can be used to focus ground-based telescopes-to correct for air turbulence and sharpen the image obtained. Such work is done at Kirtland AFB, N.M., where a large telescope at the Starfire Optical Range is used to capture images of satellites in orbit. This work paved the way for the ABL.

Down in the Weeds

At Kirtland, scientists are exploring technologies that promise to take lasers beyond the ABL. The ABL is designed to work at altitudes above 40,000 feet, where air pressure is low and turbulence is reduced. However, the Air Force Research Laboratory's Directed Energy Directorate is using adaptive optics to work in the much denser atmosphere at 8,000 to 9,000 feet. Such research would be applicable to a tactical aircraft follow-on to the ABL.

To determine how many missiles can be destroyed in one mission, knowing the distance to target is key, Booen noted. The closer the laser is to a missile, the more power can be put on it in a short period of time, quickening its destruction. At longer range, the ABL must keep the laser locked on for a longer period because the power of the laser is attenuated by distance and the atmosphere. A laser can stay locked on a target hundreds of miles away.

"What we typically have is enough for 20 shots," Booen noted, but this will vary from theater to theater. In Korea, forces and probable missile targets are found close together. There, said Booen, "it's short range, and you need less dwell-time. ... We're going to get more than 20 in a theater like that." In the Persian Gulf region, however, where the launch area may be quite far from the battle line-and hence, the ABL's orbit-each shot will require longer lasing, reducing the total number of missiles that can be killed.

Initial estimates for the ABL anticipated that each planeload of chemicals would be enough to engage 40 targets, at about $1,000 a shot. Booen will now only quote a figure of 20, to be conservative, and the price has risen to about $3,000 per shot-still orders of magnitude less than the cheapest guided missiles.

Congress raised questions about the ABL in its last budget cycle, but those have been resolved to the satisfaction of the lawmakers, Booen reported. On Capitol Hill, he said, "It seems like ... we've got a growing basis of support ... and there's only one reason it's growing: Our performance on this program is exceptional."

He reported that the Air Force has completed more than 30 percent of the program and is within 1 percent of the cost and schedule goals set at the beginning. The development program will cost $1.6 billion overall, and it is fully funded throughout the Air Force's future years defense plan. Buying and operating the ABL fleet for 20 years will cost another $9.4 billion.

Booen said that Congress did recently ask for a program restructuring, but the end result was just more risk reduction. He explained, "We've doubled the test program ... and, so far, everyone we've shown the restructure to was pretty happy with it." The expanded testing added about a year to the program's schedule.

Not Paper, but Hardware

Moreover, that 30 percent of the program which has been completed does not entail building viewgraphs and briefings, Booen pointed out. "We've got whole bunches of hardware coming through the door."

A focusing mirror that started out as an unwieldy 2,000 pounds now weighs in at just 300 pounds, he noted. Last summer, the laser was tested to 110 percent of its design power for nearly five minutes. The first of the seven planned ABL airframes will be delivered around January. The aircraft--a brand-new, off-the-assembly-line commercial 747 freighter--will be flown from the Boeing factory in Washington state to Wichita, Kan., where Boeing will modify it over 16 to 17 months into the Attack Laser-1.

Booen pointed out that the airplane will be the first to be purchased and accepted after the turn of the century, and so it will be assigned tail No. 00-0001.

The first attack laser airplane will be a test platform, but eventually it will be converted into an all-up, deployable asset. During the testing phase, there will be some limited operational capability with the test airplane, much as the first two test models of the E-8 Joint Surveillance Target Attack Radar System were rushed into service for the 1991 Gulf War, years before official operational capability was declared.

Limited capability with ABL will be available about 2004. The first three all-up models will be in service and initial operational capability will be achieved in about 2007. The last seven airplanes are to be delivered by 2009.

The Air Force is not waiting to receive the airplane before working out how it will employ the ABL in combat, however.

Notional ABLs have participated in a number of exercises and wargames in the last few years--notably Roving Sands in New Mexico and Optic Windmill in Europe--to work out its role in the battlespace. Already taking shape are where it fits on the ATO, or Air Tasking Order that governs an air campaign, as well as an awareness of what the ABL can do, Booen reported. For example, an ABL might be ordered to stay airborne even after its laser fuel is exhausted, due to its abilities as a sensor platform. The airplane has capability for air refueling and could make extended missions.

In a typical scenario, five ABLs would deploy into a theater. Two would be kept aloft at all times to cover the area of operations. A mission would probably last about 12 hours, and requirements call for a combat turn time of six hours. Each ABL could deploy with a full load of chemical fuel and even fly directly to combat from home base. A single C-17 could resupply the ABL squadron with enough chemicals for 140 additional shots.

If the ABL somehow missed a ballistic missile, its onboard computers would calculate the likely impact point and then hand off the threat to terminal point defenses like the Patriot system.

Not in Space

The possibility of using the ABL to shoot down cruise missiles or even surface-to-air missiles is being looked at, but is not a prime mission, Booen said. Though the ABL could point its laser upwards and conceivably use it in some sort of anti-satellite mission, that hasn't been examined. "It's not something we're working on," said Booen.

To cover a wider area and offer the US homeland some protection from Intercontinental Ballistic Missile attack, the Air Force has shaped a different program, the Space-Based Laser.

The SBL is in many ways a vestige of the old Strategic Defense Initiative of the Reagan era. SDI officers once envisaged an orbiting constellation of laser battle stations that would instantly spot an enemy ICBM launch and then move to destroy the missile in flight. The SBL builds on the SDI research--as well as ABL research--and is geared to demonstrate the feasibility of such a system in a single spacecraft to be orbited in 2012.

SBL's operational concept calls for shooting down ICBMs while they are still in the boost phase, when the rocket's fuel is still burning brightly. Like the ABL, the SBL would work by directing laser energy on the missile's skin to cause the booster to explode. Also like the ABL, the SBL would detect the plume of exhaust and track it. The SBL, however, would be far higher above Earth's surface, cover a much larger area, and be able to shoot missiles far deeper within enemy territory.

The SBL would be part of the ballistic missile defense system of systems now being pursued by the Ballistic Missile Defense Office, according to Lt. Col. Randall Weidenheimer, SBL program director. "It should be complementary to the ABL [in boost-phase missile attack]," Weidenheimer said, "but ABL is much nearer-term."

Congress wants to accelerate a demonstration to show that a laser can kill a missile from space, he continued. He believes Congress will add funding to the $139 million SBL program next year to advance the demonstration six years, from 2012 to 2006. However, the best estimate of research organizations is that it will take at least a decade to design and launch such a complex spacecraft, Weidenheimer said. Congress' wish to go faster may be too optimistic, and they understand that, he added.

Three major defense contractors--Boeing, Lockheed Martin, and TRW--were competing to build the SBL, but the Air Force asked them to team up in a co-equal joint venture to pursue the SBL technology. Each company had strengths, Weidenheimer said, and this arrangement allows for later competition to build the constellation, should it proceed to that stage.

The team is to report back in October as to whether they believe the program can be accelerated and, if so, by how much.

"I should note that we've been directed to be treaty compliant with this demo," Weidenheimer said, referring to the need to remain within the strictures of the 1972 Anti-Ballistic Missile Treaty signed by the United States and the Soviet Union, which has since vanished. The treaty sets out strict rules about the pursuit of ABM technologies. In late June, US and Russian diplomats agreed to reopen discussion on the ABM Treaty's limits on testing and ways the two countries might cooperate in the area.

Many Challenges

The technical challenges facing the SBL are many. They are, in essence, tougher versions of the barriers that confront the ABL program. Weight is a critical issue; the SBL cannot take as much chemical fuel to orbit as the ABL. The rigors of launch demand a hardy, yet lighter-weight laser technology than that which will be on the ABL. To achieve longer range, a larger mirror might be needed, but it would have to be folded for launch.

"We are looking at ... how viable it would be to have deployable optics," Weidenheimer reported.

The SBL will also take cues from the Space-Based Infrared System, as well as from ground-based and airborne sensors, in addition to having its own onboard infrared search-and-track devices.

The contractors have suggested building a constellation of 30 to 40 SBLs held in 800-kilometer-high orbits to achieve global coverage. The baseline SBL effort calls for using a chemical laser, since today only a chemical reaction can supply the power needed to achieve a kill on a missile. The spacecraft would be designed for refueling on orbit, Weidenheimer explained. Hydrogen Fluoride is being investigated as the chemical fuel, since an HF laser would not be absorbed by the atmosphere.

The Air Force has set 2004 as a tentative date for ground demonstration of the laser and beam control system. However, testing of how the beam would propagate in space at the necessary ranges is something that can only be done in space. Testing of pieces of the SBL may be done in orbit prior to launching the whole system. Meanwhile, the spacecraft platform on which the laser would be mounted would probably undergo its critical design review in 2006.

The Army is also exploring lasers to deal with a missile threat but on a different scale and strictly from the ground.

The Army's Tactical High Energy Laser is an advanced concept technology demonstrator that is being developed in cooperation with Israel. The system would be fielded to provide defense against small rockets, such as the Russian­made Katyusha, in situations where return artillery fire isn't an option. Such a system would be especially useful when dealing with an enemy lodged in a dense urban area.

The THEL will employ the Mid-Infrared Advanced Chemical Laser, MIRACL for short, using deuterium fluoride; it is another by-product of SDI. The Army's Space and Missile Defense Command awarded the THEL contract to TRW, which was working toward a late-summer demonstration by shooting down representative rockets at White Sands Missile Range in New Mexico. Plans call for testing to continue into 2001.

If successful, THEL would be mounted on a mobile platform and would be deployable in much the same way as the Army's Patriot air-defense system.

The ABL, SBL, and THEL are all "what we could call first-generation laser weapons," said R. Earl Good, director of AFRL's Directed Energy Directorate at Kirtland.

Enter the Zapper

At present, all the systems rely on chemical reactions to produce energy. However, the aircraft companies are telling the Air Force that they will, in a few years, be able to generate multimegawatt power using onboard generators, Good noted. Once that happens, he said, "we will enter the era of electric lasers."

Such lasers could be produced in the form of solid-state or fiber-optic systems, free of the need to carry vast quantities of chemicals around. This fact could make them applicable to aircraft as small as a fighter.

One such application, Good said, is the "Fotofighter," which would have fiber-optic lasers positioned around its airframe and wings to deal with incoming infrared-guided missiles. The lasers could blind the missiles or actually burn through their seeker arrays.

Fiber-optic lasers are at least a decade off, Good said, but it wouldn't be too long afterwards that they could be applied to aircraft defense.

"We've already talked with aircraft manufacturers about how you would run the [fiber-optic] cable through the airplane," he added.

Such systems probably represent the second generation of laser weapons, Good said. They will not arrive fast enough to be applicable to ABL or SBL but could be used on their successors.

The advantage of having a generator-supplied electric laser is that there would be an unlimited magazine of shots, he added.

Good said that lasers are not about to supplant bullets or bombs. He noted that, against a pressure vessel like a ballistic missile, lasers are uniquely useful. It would not be practical to achieve the same effect against an armored vehicle, especially when there are far cheaper ways to do it with conventional explosives, he noted.

"You're not going to burn a hole in a concrete wall or through a tank [with any of the lasers anticipated in the next 15 years]," Good said.

The promise of electric lasers won't halt research into chemical lasers, either. Miniature, pod-mounted versions of the COIL are also under study and could be tested within a few years. Such a pod would give an airplane like the F-15 a junior version of the ABL capability, with a range of hundreds of miles. The utility of such a weapon against incoming air-to-air missiles is obvious, and the technology could arrive within a decade.

It's good fortune that the ABL program is under way to help feed the SBL with technology, Good noted.

The advantage of having the ABL first as a kind of technology pathfinder is that "it lands periodically, and you do maintenance on it. So we'll learn a large amount about how a large chemical laser operates over an extended period of time," he said, and the lessons learned can be applied to the design of the SBL. Although the lasers themselves are very different with regard to their wavelengths, operating pressures, and other factors, cleaning up the beam, getting good propagation-these are engineering issues that won't require SBL to invent radically new technology, Good added.

It's still too early to assess the potential of laser weapons.

"We've just crossed the threshold, and we're just beginning [to size up the potential for speed-of-light weapons]," he said. He pointed out, though, that even the speed of light is finite. Because of the need to keep a beam tightly focused on a tiny spot on a fast-moving vehicle hundreds of miles away, even if the delay is only a few microseconds, "you've got to lead [the target], use Kentucky windage [to destroy it]."

The technology that makes ABL an emerging reality and SBL possible did not just suddenly appear. "We've been working this for 20 years," Good said. "It is the next logical step [in weapons research]."

Asked if the Air Force is going out on a limb in investing so much in lasers now, Good said it is not.

"The Air Force is a very good steward, a very responsible agency," he noted. "We don't promise things that we can't deliver. Some people get impatient with us, but we want to make sure the technology works, ... step-by-step, crawl before you walk, walk before you run. ... In that sense, the Air Force is not getting too far out [on the technology]."