GERLACH, Nev.: A car has broken the sound barrier. Twice. In two runs across Nevada's Black Rock's Desert, the jet-powered British Thrust SSC recorded speeds of more than Mach I on the ground for the first time in history. The confirmation? Two rather undramatic, barely discernible sonic booms, muffled by the desert floor. But the runs of 764.168 mph and 760.135 mph, though new land speed records by a comfortable margins, will not be entered in the books because the two runs must occur within one hour of one another to be official. On the first run, a parachute failed to deploy and the car overshot the course by more than a mile. Turning the car took 61 minutes and the record was ruled invalid. But no matter. Thrust Project Manager Richard Noble plans to exceed the speed of sound by 10 percent (Mach 1.1) before returning to England. Just to be sure.