The Lockheed Martin X-59 Quesst, sometimes styled QueSST, is an American experimental supersonic aircraft under development by Lockheed Martin for NASA's Low-Boom Flight Demonstrator project, evaluating the possibility of supersonic flight without the drawback of loud sonic booms. Preliminary design started in February 2016, with the X-59 originally planned to begin flight testing in 2021.
After repeated delays, it began flight testing in late October 2025.
