A Trident 2 missile flips out of control after being launched from a nuclear submarine off Florida Tuesday. On Wednesday the Navy began investigating why the missile self-destructed just seconds after launch in the program's first sea test. Rocky Raab, spokesman for Morton Thiokol in Utah, said the first two rocket stages of the missile were produced in a joint venture between Thiokol and Hercules. Carrying a load of dummy warheads, the three-stage $26.5 million missile was fired from the USS Tennessee. The first stage of the 126,000-pound solid-fuel missile ignited as planned. But almost instantly, the big missile began cartwheeling through the sky, exploding four seconds later. It was the fourth failure of a Trident 2 test flight in 20 launches dating back to January 1987, a 25 percent failure rate. (Additional story, A3.)