NASA says the futuristic-looking X-59 quiet supersonic research aircraft is closing in on its first flight, with engineers conducting final checks of safety systems as the program moves from ground testing toward the all-important flight-test phase. At supersonic speeds, the X-59 is designed to replace the ear-splitting sonic “boom” heard on the ground with a muted “thump,” NASA said. Safety has been a central theme as the program nears first flight, NASA stressed. The aircraft carries a Flight Test Instrumentation System that logs 60 data streams and more than 20,000 onboard parameters. The X-59 is central to NASA’s Quesst mission, a multi-year effort to gather noise data that will be shared with regulators worldwide.