In partnership with NASA, the Lockheed Martin Skunk Works team is solving one of the most persistent challenges of supersonic flight – the sonic boom. NASA awarded Lockheed Martin Skunk Works a contract in February 2016 for the preliminary design of the supersonic X-plane, designed to reduce a sonic boom to a gentle thump.In 2018, Lockheed Martin Skunk Works was selected for the design, build and flight test of the Low-Boom Flight Demonstrator (LBFD). The LBFD aircraft will collect community response data on the acceptability of the quiet sonic boom generated by our design, helping NASA establish an acceptable commercial supersonic noise standard to overturn current regulations banning supersonic travel over land. 
This would open the door to an entirely new global market for aircraft manufacturers, enabling passengers to travel anywhere in the world in half the time it takes today.
The X-plane is designed to cruise at 55,000 feet at a speed of about 940 mph and create a sound about as loud as a car door closing, 75 Perceived Level decibel (PLdB), instead of a sonic boom.
Source: Press Release