Son-of-Concorde may not be daydream for much longer with NASA awarding a US$247.5 million contract to Lockheed Martin to design, build, and test a prototype supersonic aircraft capable of generating no more noise than a car door closing while flying faster than the speed of sound over populated areas. The cost-plus-incentive-fee contract is aimed at producing the Low-Boom Flight Demonstration X-plane that NASA hopes will prove it's possible for regular supersonic passenger services to operate over land and will help to write new environmental regulations.

Ever since the last of the Anglo-French Concorde fleet was grounded in 2003, the aerospace industry has been working on ways to reintroduce supersonic technology to commercial aviation. Among the many hurdles that engineers face in making a new generation of supersonic liners is the infamous sonic boom.

Caused by the build up of a shockwave in front of an aircraft as it flies faster than the speed of sound, a sonic boom can exceed 200 decibels, causing all sorts of disruption to civilian life, livestock, and even cracking the odd window. It's for this reason that supersonic passenger flights in the past have been restricted to international flights over open water.

The contract awarded to Lockheed that runs through December 31, 2021 is to take care of the engineering side of the equation by creating and testing a new X-plane that can cruise at 55,000 ft (16,700 m) at a speed of 940 mph (1,513 km/h, Mach 1.2), yet generates only 75 Perceived Level decibels (PLdB) – a sonic thump instead of a boom.

Meanwhile, NASA will take care of the other side of the equation. It wasn't just the sonic boom that crippled the Concorde, but the environmental regulations passed in the 1970s to control it. These regulations relied on old science and were often written with prejudice against supersonics, so the agency wants to revisit them on the US and international levels.

As part of this NASA will, after taking delivery of the prototype, conduct its own flight tests to both confirm Lockheed's findings and to fly it over select US cities to gauge public opinion.

The video below introduces the concept of the sonic "thump."