It's taken nearly three years. But the Homeland Security Department is finally ready to start testing out missile countermeasures on commercial planes.

Back in November 2002, an Israeli 757 was attacked with two shoulder-fired MANPADS (man-portable air defense systems) over Kenya. Luckily, the missiles didn't connect. But many analysts think it's only a matter of time before an American jetliner is hit; MANPADS have killed hundreds of airline passengers since the 70's. And unless some kind of countermeasure is put in place, the planes will continue to be "almost like sitting ducks. Those aircraft are very slow... Everyone can [attack them]," an Israeli defense researcher told CNN.

Military planes are already equipped with "Directional InfraRed Counter-Measures," or DIRCMs, which use laser beams to confuse the missiles' guidance systems. But just slapping the military systems on commercial planes would cost a ton -- $11 billion, maybe, to install DIRCM on all 6,800 U.S. commercial jets, plus another $40 billion in maintenance over 10 years, according to a Rand study.

Northrop Grumman and BAE Systems have been working on cheaper, easier-to-maintain versions of the countermeasure. And Northrop says it should be ready to begin "operational testing and evaluation... aboard an MD-11 airliner later this month and a Boeing 747 later this year."

A company spokesperson says that the system "will cost airlines $0.003 to operate per available seat mile or about 70 cents per passenger on a 2,000-mi. trip. This is about the cost of a bag of peanuts," Aviation Week notes. "However, there is a weight penalty with the system. The Northrop Grumman installation weighs 500 lb., including 350 lb. for the pod, about the weight of two passengers and bags."

It's still a significant cost for already-troubled airline companies. But given the countless thousands of MANPADS floating around on the international market -- selling for as little as $5,000, according to Rand -- a bag of peanuts and two extra passengers seems like a price worth paying.