Infrared Countermeasures

Queen Elizabeth probably isn't the first person who comes to mind when you think "early technology adopter." But back in the early 1990s, her official aircraft—as well as Air Force One—was secretly outfitted with a directed infrared countermeasures (DIRCM) system to protect it from a missile attack.

The technology isn't top-secret any more. When terrorists fired a pair of infrared (IR) SA-7 surface-to-air missiles (SAMs) at an Israeli passenger jet in Kenya late last year, the near-disaster called attention to commercial aircraft's vulnerability to small, shoulder-launched weapons. With an estimated inventory of 500,000 shoulder-launched IR missiles around the world, IR jammers may become more important to air travelers than comfortable seats and in-flight movies.

A DIRCM system confuses the IR seeker in the nose cone of an incoming missile, prompting it to plow into the ground well short or well wide of its intended target. An on-board DIRCM system first warns of an incoming IR missile up to 10 miles away and then hands off the information to a jammer. This jammer uses an IR tracker to follow the missile and guide a laser beam onto its nose, which houses the IR seeker. The system then transmits jamming signals that send the missile off target.

Here's where things get really complicated. For each IR missile type, there is an optimum set of jamming algorithms. Since a DIRCM system can't identify specific missiles, it uses generic jamming algorithms or else sequences through a catalog of specific jamming codes. The IR tracker measures the effectiveness of the jamming as it tracks the incoming missile. Through trial and error it determines which algorithms work—all in as little as 3 seconds.

The challenge now is to build smaller and more powerful lasers. Under its Steered Agile Beams (STAB) program, the Defense Advanced Research Projects Agency is investigating new technology for replacing the bulky, mechanical DIRCM turrets with electronically steered laser arrays that conform to the shape of an aircraft. This would minimize drag and direct the lasers much faster. Since most IR surface-to-air missiles can fly at speeds from Mach 2 to Mach 4, a typical missile engagement is over less than 8 seconds after launch. The faster the laser can be directed onto the missile's seeker the better.

Meanwhile, the U.S. Air Force and Lockheed Martin are developing a closed-loop IR countermeasures (CLIRCM) technology, which can identify the type of IR missile and transmit the optimal jamming code on the first try. "CLIRCM technology is able to counter any type of known or unknown threat, extending its effectiveness well into the future to defeat SAMs not yet fielded," says John Wojnar, advanced programs business development director at Lockheed Martin.

A CLIRCM system on board an aircraft can jam a threat by scanning the ground and detecting the cat's-eye reflection from any missile pointed in its general direction. It can then start jamming before a missile is launched. Air Force officials refer to this as "keeping the missile on the rail."

The one problem with DIRCM technology is its high price tag—between $1.5 million and $6 million per system. For military aircraft that spend a lot of time in the threat envelope (below 15,000 feet), the technology is well worth the price. For the struggling airline industry, though, the question is whether the costs outweigh the benefits.