An MX intercontinental ballistic missile tipped with seven dummy warheads rocketed into the sky and hit its targets 4,100 miles away in the Pacific Ocean, officials said. The launch from Vandenberg Air Force Base, 150 miles northwest of Los Angeles, was the Air Force’s 18th in a series of 20. But officials said they may have gained enough information from the program to make the latest launch the last. The Peacekeeper missile traveled for about 30 minutes before its warheads split away and hit their targets at the Kwajalein Missile Test Range in the Pacific Ocean, said Capt. John Sullivan. The MX is designed to carry as many as 10 nuclear warheads.