The airborne laser is a Boeing 747-400 jumbo jet with the world's largest and most powerful laser on board. It's designed to be the center of a solid Theater Ballistic Missile Defense, but many also see it as the first tier in a four-tiered National Missile Defense. Flying at altitudes of 40,000 feet or higher, the ABL would act as a boost phase interceptor. Given the short burn times of today's missiles, the ABL would have less than five minutes to acquire a newly-launched missile, lock onto one spot on the missile's surface, and burn a hole through that spot. On a solid-fuel rocket, the target area would burn rapidly, either pushing the missile into a hard turn or causing the missile to burn itself up. On a liquid-fuel rocket, the target area is likely to be either the fuel tank or the oxidizer tank, and the result would almost certainly be an onboard explosion. The obvious advantage is that the missile never leaves the country that launched it. The main disadvantage is that the expensive, vulnerable airframe has to be within laser range of a missile launch--most likely enemy airspace, requiring fighter escorts.