Can Supersonic Air Travel Fly Again?

In his view, speed, economy and reduced emissions can be achieved through cleaner fuels and new engines designed expressly for supersonic flight. This approach contrasts with that of the Concorde, which used “converted military engines that were super-inefficient and rip-roaring loud,” Mr. Scholl said. (There are no realistic estimates on how or when such engines will be available.)

These engines — as well as modern materials, building methods and efficiencies introduced since the 1970s supersonic vogue — would let Boom operate for 75 percent less than the Concorde, Mr. Scholl said, although he added that his goal was to be 95 percent less expensive. Even so, he estimated initial fares at about the cost of a business-class ticket. “Still a long way from $100,” he acknowledged.

A handful of companies have proposed private supersonic business jets to whisk international bankers, chief executives and hedge fund managers around the globe in swift, exclusive opulence. But despite the stated intentions of established players such as Gulfstream and credible upstarts like Spike Aerospace, private supersonic jets have yet to streak across the skies.

The chief barrier appears to be economic. It is the norm for aircraft to take longer and cost more to build than projected, and private supersonic jets are no exception.

NASA has government backing and shares much of its research so that any aerospace company can benefit from it, although it does not work with any specific airline or manufacturer. But without government financing, it is tougher for companies like Gulfstream and Boom. There is a cautionary tale in the experience of Aerion Supersonic, a company of aviation veterans that was underwritten by the billionaire Robert Bass, in partnership with Boeing, and that claimed preorders of $11.2 billion. Unable to raise enough cash to keep the doors open, Aerion shut down in May and is now being liquidated in a Florida court.

While supersonic travel would be a boon to international trade, there are too many unknowns to predict its viability as a business, said Bijan Vasigh, who teaches economics at Embry-Riddle Aeronautical University. “Are there 50 people a day who want to fly to London?” he asked. “Do we know how much people are willing to pay?”

He added: “We do our best analysis, but everything in the future could change. The best economist cannot find the answer.”