Aerospace engineer David Graham and his three colleagues had a deadline, and a little brown tortoise was putting it in jeopardy. In a few hours, as the sun rose over the Mojave Desert on an August morning last year, two Northrop Grumman F-5E fighter jets would come racing over the horizon. Flying 30,000 feet above Harper Dry Lake and traveling at 920 mph, the airplanes would be trailing long sonic booms–the distinctive aural signatures of supersonic flight that ordinarily make high-speed passages over land impossible.

The engineers, all members of a Northrop Grumman led research team working to make those signatures significantly less distinctive, expected the two booms would be different from one another–a difference too slight to hear, even with your ear cocked to find out whether a 30-year-old theory aimed at mitigating supersonic shock waves worked in the real, turbulent and bubbly atmosphere, but one big enough to be detected by the instruments in the back of their SUV.

But this SUV, crammed with gear that had to be set out across the lake bed, wasn’t going anywhere until the desert tortoise moved its reptile rear out of the way. The Bureau of Land Management’s instructions were strict: Startling the endangered animal could threaten its life. The predawn hours are the male desert tortoise’s time to roam in search of water, food and female company. That is arduous work, as every tortoise knows, and sometimes a guy just needs a rest. It was 15 long minutes before the beast waddled on its way.

Finally on the lake bed, NASA investigator Ed Haering supervised the placement of the portable instrument packages he’d designed, each containing an ultrasensitive Brüel & Kjaer 4193 microphone, in an array about 2.5 miles wide. Away to the north, Northrop test pilot Roy Martin lined up his F-5E, which Graham had disfigured until Welko Gasich’s elegant 1956 design was barely recognizable. Martin pushed the stick forward and the pelican-nosed F-5E began to pick up speed in a shallow dive, accelerating through the sound barrier.

More here.