This article is part of our series on the Future of Transportation, which is exploring innovations and challenges that affect how we move about the world.
Despite the promise of two-hour flights from New York to Los Angeles, the supersonic airline industry never really got off the ground. That is largely because of physics: specifically, the sonic boom, the thunderclap noise made when an aircraft breaks the sound barrier (and continues as the aircraft flies beyond the barrier), which essentially doomed supersonic aviation as a viable business.
In 1960s-era tests, booms reportedly broke windows, cracked plaster and knocked knickknacks from shelves; in 1973, the Federal Aviation Administration forbade civilian supersonic aircraft from flying over land. Planes could go supersonic only over the ocean — most famously, the Concorde, the sleek British-French passenger plane that flew a handful of routes in less than half the average time. But potentially lucrative overland routes were off limits, restricting supersonic travel’s business prospects.
NASA and aviation entrepreneurs, however, are working to change that, with new aircraft designed to turn the boom into a “sonic thump” that is no louder than a car door that is being slammed 20 feet away. That may induce the F.A.A. to lift the ban, which could allow for two-hour coast-to-coast supersonic flights.
“The main reason NASA is working on this is to enable regulation for supersonic flight,” said Craig Nickol, NASA’s low-boom flight demonstration project manager. “The main objective is to open up new markets.”
The supersonic age dawned on Oct. 14, 1947, when Chuck Yeager broke the sound barrier while piloting the rocket-powered Bell X-1 over the Mojave Desert. In the following decades, the barrier was also broken by a succession of military jets, once by a passenger airliner (during a test flight of a Douglas DC-8 in 1961) and, ultimately, by regular commercial service from the Soviet Tupolev Tu-144 and the Concorde, both long defunct.
The far more successful Concorde mostly traveled trans-Atlantic routes at about $6,000 to $7,000 per ticket for a three-and-a-half-hour flight in a cramped, noisy cabin, which was nonetheless considered glamorous. The Champagne-and-caviar flights were discontinued in 2003 after 27 years of intermittent profitability and one crash that killed 113 people. What the Concorde’s chief pilot called “the airliner of the future” was consigned to the past.
But the possibility of a supersonic renaissance was arriving even as the Concorde was on its way out. The slide rules and log tables used to design it had been pushed aside by supercomputers, which enabled engineers to test and tweak virtual aircraft designs comparatively cheaply and quickly.
That is exactly what Darpa, the research and development wing of the U.S. Defense Department, and NASA did in 2003 with the Shaped Sonic Boom Experiment, which confirmed that computer-designed modifications to a Northrop F-5E jet would hush the sonic boom in the way the software forecasted. “We flew it and measured it, and our model predicted the boom very well.,” Mr. Nickol said. “It was the first time we could prove that we could shape the sonic boom in a way we could predict.” That demonstration set the course for research to follow.
Taming the boom is complicated. Air has substance, which an aircraft slices through, much as a boat moves through water. A plane pushes air aside as it flies, creating ripples of air pressure. As an aircraft approaches the speed of sound, pressure builds up on surfaces like the nose and tail, creating waves of high pressure in front and low pressure behind. At the speed of sound, waves pile up and combine to reach the ground as an abrupt change in pressure that is heard as that thunderclap sound.
“It’s the change in the pressure that makes the sound,” Alexandra Loubeau, a NASA acoustics engineer, said. And that boom happens not just when a plane first breaks through the sound barrier; it also trails the jet continuously, like a boat’s wake.
NASA research led to the X-59 QueSST (for Quiet Supersonic Technology), a needle-beaked aircraft with lift and control surfaces spread over the 100-foot fuselage, of which 33 feet are nose.
The shock waves of a sonic boom cannot be avoided completely, but by minimizing the surfaces where pressure builds up — like the air intake and control surfaces — and spreading them over the length of a fuselage, shock waves can be reduced, shaped and aimed. “You can modify the aircraft to alter what the wave looks like when it hits the ground,” Mr. Nickol said. “What we are doing is trying to spread those waves out and make them weaker.”
NASA is not alone in trying to re-establish supersonic travel. Blake Scholl, chief executive of the Denver-based company Boom Supersonic, has declared an audacious goal of delivering passengers anywhere in the world within four hours for $100. He said Boom would begin with international transoceanic supersonic service, so that it would not have to worry about noise or wait for regulation changes, although domestic routes would mean more passengers, giving the business “a huge boost, a factor of two- or three-times in opportunity,” he said.
Mr. Scholl added that he thought that just making faster aircraft would not create a sustainable supersonic business; planes must also be faster, cheaper and eco-friendly. The effort “has to be 100 percent carbon-neutral,” he said.
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.”
Adam Pilarski, an aviation economist and consultant, agreed that the numbers were uncertain, but still expects to see supersonic aircraft produced, although not by a major aircraft manufacturer. “It will make all of their other planes obsolete,” he said.
Instead, he looks to a maverick outfit on the order of Elon Musk’s venture with Tesla or Space-X. “When Musk started going to space, who believed him? Nobody!” Mr. Pilarski said. “The C.P.A.-type thinks, ‘How much people will pay?’ Who cares?”
Although Mr. Pilarski predicts eventual success for a supersonic airline, he is reluctant to place any bets. “Will Blake Scholl make it?” he asked. “I don’t know, he is a nice boy. But would I put my money on it, and grandchildren’s education fund on it? No.”