As Israel’s air raid sirens rang out to warn of an incoming rocket during the recent conflict with Gaza, they were joined by another sound. On the outskirts of the city, a cutting edge system locked on to the incoming rockets, worked out their likely trajectory and then in many cases fired its own interceptors to knock them out of the sky. During the short conflict, the roar of Israel’s Iron Dome was a regular sound.

The new anti-missile batteries were heralded as a great triumph, being fired 573 times and hitting 421 out of 1,506 missiles fired from Gaza, according to Israel’s defence ministry.

Iron Dome was first fielded in 2011 after Israel’s government decided against a more exotic missile defense system that used lasers. But now, defence firms say that so-called directed energy technology is still progressing and soon these silent weapons could be ready for their big test.

One of the main players is US defence giant Lockheed Martin. Less than a week after the ceasefire, the company revealed that it was working on a new laser system, called Area Defense Anti-Munitions (Adam), designed to shoot down similar projectiles. It says it has even conducted a test of the system, which uses a solid-state fibre laser, to destroy small-caliber rockets from 1.2 miles (2km) away.

Although it put out a press release, Lockheed is keeping a close hold on its technology and the company declined interviews about the ground-based weapon. “We have demonstrated that the commercial 10-kilowatt laser, when focused by our innovative beam control software, has sufficient power to negate the close-in threats…,” Lynn Fisher, a Lockheed spokeswoman told BBC Future. “At this time, 10 kilowatts is the highest single-mode power available in a commercial laser with sufficient beam quality for this application.”

Lockheed is one of several firm’s that has pursued laser weapons since the 1970s for a range of applications and military services. The Army has already used lasers for exploding mines and ordnance, whilst the Navy is interested in using them to “neutralize threats”, including drones, boats or missiles. In 2011, it released a video of a test in which its so-called Maritime Laser Demonstrator burnt a hole in the engine of a small boat.

Other firms, such as Northrop Grumman already have developed a mobile weapon called the Firestrike,  which the company says it powerful enough to be used on the battlefield—or at sea.

Toxic trouble

However, despite being long promised, the use of laser weapons is limited. The systems that exist today are often too big or complex for real world applications. And critics say the latest burst of interest merely reflects a decades’ long tendency to overestimate the capabilities of lasers, while underestimating the operational and technical difficulties of using such weapons for missile defence.

One example of this was the Airborne Laser, which was to be flown in the nose cone of a Boeing 747 and was designed to take down intercontinental ballistic missiles in their vulnerable boost phase. Former Defense Secretary Robert Gates, said the operational concept, which involved flying an undefended plane into potentially hostile areas, was unrealistic and canceled the project.

Other laser projects have suffered similar fates. Subrata Ghoshroy, a research associate at the Massachusetts of Institute of Technology, recalls working as a congressional staff member in the mid-1990s when he was briefed on the Nautilus laser, which was jointly sponsored by the United States and Israel.

Nautilus was a chemical laser, so-named because it obtains its energy from a chemical reaction, which was designed to shoot down Soviet Katyusha rockets. Even then Ghoshroy expressed his doubts about the project, however.

“This particular laser was using deuterium fluoride, chemical laser technology, which is extremely toxic and difficult to handle,” he says. “There would be canisters of this stuff sitting in the desert; one Katyusha rocket hitting a canister is a huge problem.”

The developers were eventually able to demonstrate on a test range that they could take down a rocket, but the tracking system wasn’t very good, according to Ghoshroy. After a decade of effort and hundreds of millions of dollars, the laser effort was cancelled, and Israel instead deployed Iron Dome.

“My concerns were validated once the whole thing was abandoned,” he says.

Ivan Oelrich, a defense analyst who has advised on military technology issues for several decades, is equally dubious of the near-term prospect of laser weapons for defeating rockets and missiles. “The problem is these things look great when you test them at White Sands,” says Oelrich, referring to the Army range in New Mexico used for testing lasers. “In the real world, all these lasers have limitations based on what’s going on in the atmosphere.”

Haze, fog, or other poor weather conditions can degrade the laser’s effectiveness—and that provides an advantage to would-be attackers. “If I know I’m going to have a cloudy day tomorrow, I’ll launch my rockets then,” says Oelrich.

Money talks

Oelrich suggests that another problem is that attackers might be able to come up with simple countermeasures to such laser weapons, such as painting their rockets white, which would allow them to reflect heat. Or, another idea, slightly more technical, but still easily doable, is to find out what the wavelength of the laser would be, and then cover the missile with material that would deflect it.  “It doesn’t add a lot of weight, so why would I not do that?” he says.

Yet there are still laser enthusiasts who argue that the technology has a role to play as part of a more comprehensive approach to missile defense. Mark Gunzinger, a retired Air Force colonel and former Pentagon official, argues that new high-power lasers, particularly newer solid-state lasers, offer a “complementary approach” to systems that deploy interceptors.  

One of the problems pointed out with interceptors, such as Iron Dome, is that it often ends up costing much more for the defender to take down a rocket than for an aggressor to launch it. Laser weapons, by contrast, are theoretically cheaper since they can shoot a near infinite number of times.

Gunzinger, now a senior fellow at the Washington, DC-based Center for Strategic and Budgetary Assessments, argues that laser weapons have the potential to change “the negative cost ratio back in your favor.

While Gunzinger points to growing support for solid-state lasers, particularly from the Navy, he says a chemical laser like the one developed for the Airborne Laser could prove useful.  “You could take an upgraded version of the Airborne Laser’s weapon system and use it to defend forward areas, forward air bases, from medium and even short range ballistic missiles,” he says. “The technology is there: It’s a question of if someone wants to fund it.”

And that’s the problem - with the US administration facing the fiscal cliff, the prospects of funding a major laser weapon system is unlikely at best.

But even if it were affordable, it’s not clear it’s desirable. “One of the things you have to ask yourself when dusting off an old idea is that if we decided not to do this last time, what’s different now?” says Oelrich. For laser weapons that answer still may be unclear.

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