The legendary supersonic Concorde jet used to ferry passengers across the Atlantic in just three and a half hours at twice the speed of sound. Impressive, for sure, but NASA now says it's exploring the possibility of doubling that.

After completing a survey of business cases for the use of supersonic jets able to travel between Mach 2 - 1,535 mph (2,467 kph) - and a blistering Mach 4, or 3,045 mph (4,900 kph), NASA concluded there are around 50 established routes that could benefit from such aircraft. 

As far as the space agency is concerned, that's enough to justify a pair of new contracts issued to Boeing and Northrop Grumman to figure out if it's even possible to build a passenger jet that can fly that fast. 

A vexatious velocity

"We conducted similar concept studies over a decade ago at Mach 1.6-1.8, and those resulting roadmaps helped guide NASA research efforts since," said Lori Ozoroski, NASA Commercial Supersonic Technology project manager. 

Those tests, Ozoroski explained, led to the development of new supersonic test craft like the X-59, which is almost ready to begin ultra-quiet test flights to determine if better designed supersonic aircraft can be less tooth-rattling than the Concorde.

Of course, the X-59 isn't nearly as fast as the Mach 2-4 passenger jets NASA is brainstorming, meaning it'll probably be far quieter. Civilian supersonic flights over land are banned in the US and other countries due to sonic boom issues. NASA isn't exploring any overland routes for its Mach 2-4 project, only flight paths that are over sea are being considered.

That said, air speed records for manned aircraft suggest getting up to Mach 4 in a passenger jet would be an immense technical feat - the Concorde set passenger jet records with its roughly Mach 2 cruising speed, and official air speed records are currently held by the USAF's SR-71 Blackbird which, reaching speeds of 2,193 mph (3,529 kph), only made it to Mach 2.85. 

Beyond the SR-71's speed record we're looking at experimental rocket planes and uncrewed hypersonic scramjets and gliders used as missiles, not passenger craft. 

What, then, are Boeing and Northrop going to be doing? Developing "concept designs and technology roadmaps," NASA said. 

Both teams will be working on airframe, power, propulsion, thermal management and materials able to handle high-supersonic speeds, as well as creating non-proprietary designs for concept vehicles. 

"There are several key technical challenges that will need to be addressed to enable a high-speed vehicle," Mary Jo Long-Davis, NASA's Hypersonic Technology project manager told The Register.

While noise isn't so much of a concern since the project is focusing on ocean routes, takeoff and landing noises are still an issue, Long-Davis said, as are high-altitude emissions. All of that, of course, ignores the simple challenges of getting such an aircraft certified, Long-Davis added.

"The design concepts and technology roadmaps are really important to have in our hands when the companies are finished," Long-Davis said. Regardless of what's possible, however, "it's important to innovate responsibly so we return benefits to travelers and do no harm to the environment," Long-Davis added. 

The space agency didn't provide a timeframe for the project. Long-Davis only added that potential Mach 2-4 aircraft are likely "much further down the line" than newer Mach 1.5-2 aircraft, designs for which could emerge as a result of the X-59 experiments, Ozoroski told us.

However, the completion of the Boeing/Northrop phase of industry engagement doesn't even guarantee the project will continue. Once the contractors report back with their results, "NASA and its industry and academic partners will decide whether to continue the research with their own investments," NASA said. ®

https://www.theregister.com//2023/08/24/never_mind_the_concorde_nasa/