Those still nostalgic about the Concorde can take heart because a new era of supersonic flight just came a step closer. NASA says that its Quiet Supersonic Transport (QueSST) project has passed its preliminary design review (PDR), opening the way for design and construction of the Low Boom Flight Demonstration (LBFD) X-plane.

Reviving civilian supersonic passenger travel isn't simply a matter of finding someone to put up the money to build a fleet of Concorde Mark IIs. There are many technical problems that need to be solved before airliners capable of traveling faster than the speed of sound can once again take to the skies. The most significant is finding a way to reduce or eliminate the window-cracking sonic booms that confined Concorde solely to oversea flight paths.

In February 2016, NASA gave the green light to the QueSST project, which tasked Lockheed Martin and its subcontractors under a US$20 million contract to take a set of NASA feasibility studies on how to make supersonic aircraft safe to fly over land and turn it into preliminary designs for a manned demonstrator aircraft that would use new fuselage, wing, and engine designs to create a supersonic "heart beat" or soft thump rather than the booms of present supersonic airplanes.

On Friday, senior experts and engineers from Lockheed and NASA concluded that the QueSST design has reached the point where it can fulfill the LBFD X-plane's mission objectives. In addition to being able to fly supersonic without the boom, the single-engine manned plane must be able to fly over populated areas, so the NASA, the FAA, and other regulators can determine if over land flights are practical and to help in updating regulations on supersonic flight that still remain frozen in the 1970s.

So far, the QueSST preliminary design has been subjected to supersonic wind tunnel tests at NASA's Glenn Research Center in Cleveland and is going on to static inlet performance test and a low-speed wind tunnel test at NASA's Langley Research Center in Hampton, Virginia, to help finalize the design. The project team will now begin soliciting proposals to build the LBFD demonstrator with contracts to be awarded in early 2018. Flight tests are scheduled for as early as 2021.

"Managing a project like this is all about moving from one milestone to the next," says David Richwine, manager for the preliminary design effort under NASA's Commercial Supersonic Technology Project. "Our strong partnership with Lockheed Martin helped get us to this point. We're now one step closer to building an actual X-plane."