Sept. 22 (Bloomberg) -- Northrop Grumman Corp., the largest maker of unmanned aircraft for the U.S. military, demonstrated a high-altitude defense that could be installed on unpiloted drones to protect airports against shoulder-fired rockets.

From heights exceeding 50,000 feet, the system successfully detected, tracked and directed a laser to intercept a target missile, Jack Pledger, Northrop's director of infrared counter- measures, said in an interview today. The system worked in all three tests at Holloman Air Force Base in New Mexico on Sept. 8 and 9. A fourth test was scrapped when the target malfunctioned.

The trials were run under a $6.6 million contract from the U.S. Homeland Security Department to show the feasibility of using unmanned aircraft above airports to defeat shoulder- launched, heat-seeking missiles fired at commercial aircraft. For the demonstration, Northrop modified the Guardian countermeasure system it has tested on jetliners for 13 months.

A high-altitude system ``would provide another layer of protection to focus on heavy traffic areas, or areas of concern,'' Pledger said. ``We demonstrated what can be done today and what needs to be done to move this technology forward.''

The Guardian, which directs a laser to jam the heat-seeking guidance systems on rockets, has acquired 10,000 hours of flying time on 4,600 commercial flights. Northrop modified Guardian for high altitude and tested it from the White Knight aircraft that launched SpaceShipOne in 2004 as the first private, manned spacecraft. Northrop bought Scaled Composites LLC, maker of White Knight, last year.

Northrop will deliver a report to Homeland Security by March on what would be needed for a complete unmanned, high-altitude system, Pledger said.

Terrorists launched two missiles that narrowly missed an Israeli passenger jet in Kenya in 2002.

Los Angeles-based Northrop had sales of $32 billion last year and is the world's largest warship maker. Northrop fell $1.42 to $64.10 at 4 p.m. in New York Stock Exchange composite trading.

To contact the reporter on this story: Edmond Lococo in Boston at elococo@bloomberg.net.

Last Updated: September 22, 2008 16:11 EDT