A Navy heat-seeking missile is getting its first real-world use in an attempt to demolish a crippled US spy satellite before the orbiting craft falls back to Earth. The targeting of the satellite - which could come Wednesday night - is not the mission for which this piece of the Pentagon's missile defense network was intended, however. The attempted shootdown, already approved by President George W. Bush out of concern about toxic fuel on board the satellite, is seen by some as blurring the lines between defending against a weapon like a long-range missile and targeting satellites in orbit. The three-stage Navy missile, designated the SM-3, has chalked up a high rate of success in a series of tests since 2002, in each case targeting a short- or medium-range ballistic missile, never a satellite. A program to adapt the missile for this anti-satellite mission was completed in a matter of weeks; Navy officials say the changes will be reversed once this satellite is down.