NASA really wants us to be able to travel between New York and Los Angeles in two hours. Supersonic flight — flying faster than the speed of sound — could make it happen, except that it involves an ear-deafening “sonic boom” that’s not allowed by the Federal Aviation Administration (FAA). But as of Monday, NASA has completed a preliminary design review (PDR) for a supersonic plane that will actually be quiet enough for use.

The project is called the Low Boom Flight Demonstration experimental plane (LBFD X-plane), and NASA’s been designing it with the Lockheed Martin Corporation since February 2016. The two partners have been testing a small model of the plane in wind tunnels this year, and now they’ve finished reviewing the initial design (referred to as the QueSST design, for Quiet Supersonic Transport) and approved the construction of a full prototype.

Supersonic flight creates shock waves and expansion waves that usually produce a boom, but the QueSST design separates these waves and guides them into an arrangement that eliminates the boom. While a shock wave normally leads to a sudden pressure change, this design creates a gradual rise in pressure. NASA released a video on Monday that illustrates the process:

supersonic plane
A visual from NASA illustrating how the shock waves from the plane are arranged to eliminate a sonic boom.

Now that the design has been reviewed, NASA will seek contractors to build the full-scale prototype. “Flight testing of an LBFD X-plane could begin as early as 2021,” reads the agency’s press release.

When NASA tests the full prototype, it will assess how the plane’s noise affects real communities; the agency hopes to gather data that will encourage the FAA to change its regulations and allow supersonic flight. “The real data for regulatory change requires really taking measurements on the ground,” says David Richwine, manager for the Quiet Supersonic Technology Project, in NASA’s video, “and then doing surveys of the population to see what the annoyance of those much quieter sonic booms are.”

Supersonic Boom Quiet Plane
An illustration of the planned Low Boom Flight Demonstration aircraft.

The PDR covers the preliminary design’s risks, costs, testing verification methods, construction timeline, and other important aspects. Even though this review is done, NASA still has a few final tests to perform on the plane before the design is completely finalized. The PDR is a huge step, though, and allows the agency to begin soliciting proposals from potential builders of the X-plane.

Once the LBFD X-plane is built and successfully tested, how might it be before commercial airlines begin designing, building, and using supersonic planes?

NASA’s J.D. Harrington told Inverse that we really can’t be sure, because it’s not up to the agency. “NASA’s mission is to provide data to prove a specific technology works effectively,” he said. “It’s up to manufacturers to make the business case and decide whether to implement that technology.”

Check out the video NASA released about the project below.

Photos via YouTube user: NASA Langley Research Center, NASA / Lockheed Martin