But the race comes at a crucial moment. Airline revenue was decimated by the coronavirus pandemic, putting pressure on companies to find more revenue sources as they slowly recover. As climate change accelerates, carriers are facing pressure to expand their operations while keeping carbon emissions to a minimum.

Meanwhile, technical challenges remain. Jet engine technology, noise regulations and the shortage of clean and alternative aviation fuel will make it difficult for airlines to get government approvals on aircraft and keep ticket prices low, critics said. Bold corporate claims of bringing back supersonic travel will run headlong into scientific challenges for years to come, they added.

“These manufacturers are trying to reinvent supersonic aircraft,” said Dan Rutherford, director of the aviation program at the International Council on Clean Transportation. “But they can’t reinvent the science — and the science is actually pretty damning.”

Supersonic travel has captured the imagination of aviators for decades. In 1947, U.S. Air Force Capt. Chuck Yeager became the first person to fly at supersonic speeds, inspiring commercial aviation companies to follow suit. In 1962, the British and French governments signed a pact to develop a supersonic jetliner, called the Concorde.

In 1976, the Concorde made its commercial debut with two airlines — British Airways and Air France. Over the next two decades, the plane grew into a symbol of luxury life. Champagne, caviar, lobster and lamb were on the menu. Hollywood celebrities, athletes and business moguls were photographed boarding the plane. The jet would fly at 60,000 feet, getting passengers from New York to London in just around three hours, cutting travel time nearly in half.

Despite the glamour and speed, significant problems plagued the jet. It created a sonic boom that was so loud that airlines were able to fly above the speed of sound only over water. The jet consumed huge amounts of fuel, forcing ticket prices up; a round-trip airfare between New York and London cost $12,000 in the early 1990s.

The jet’s engines also were noisy, drawing anger from residents that lived near airports with Concorde jets. And in 2000, an Air France Concorde flight from Paris to New York burst into flames, crashing into a hotel shortly after takeoff and killing 113 people, creating an image problem that was hard to recover from.

“It was more expensive to run [and] too large to be economically viable,” said Iain Boyd, a professor of aerospace engineering at the University of Colorado in Boulder. “And then they had an unfortunate accident … and I think that was the straw that broke the camel’s back.”

Since the Concorde’s last passenger flight in 2003, there had been little attempt to resuscitate the service, until recently.

Over the past decade, numerous start-ups have cropped up promising a better, more cost-effective supersonic jet for commercial air travel. Earlier this week, Canadian business jet manufacturer Bombardier successfully tested a smaller private jet at supersonic speeds, called the Global 8000. Cost: $78 million per jet.

Blake Scholl, the chief executive of Boom Technology, a Denver-based company founded in 2016, said his company hopes to have a supersonic jet, called the Overture, in the skies by 2029. Later this year, the company will break ground on its production facility in South Carolina.

Scholl added that his company’s supersonic jet, which could seat 65 to 88 passengers and fly at just under twice the speed of sound, will cost airlines $200 million a piece. United Airlines has a firm order for 15 planes, he said, which could increase by up to 35 more. Japan Airlines has said it could purchase up to 20 aircraft, Scholl added.

He said that the company won’t replicate the failures of the Concorde for multiple reasons. Carbon fiber technology has improved since the 1960s, allowing the Overture to be lighter and more fuel efficient than the Concorde. Software is better, allowing his team to build a more aerodynamic plane. And his company plans on using sustainable aviation fuel — which is an alternative fuel derived from plant waste and other organic matter — allowing Boom to be more environmentally conscious.

“All of that put together means that for Overture One, airlines will be profitable,” he said.

Mike Leskinen, president of United Airlines Ventures, said his company’s bet on supersonic travel will fill customer demand for high-speed business travel. It plans to put most of the planes on routes from Newark International Airport to London by the end of the decade, with possible legs to Paris, Amsterdam and Frankfurt.

United would configure the aircraft to seat around 80 or so passengers in business class seats similar to the ones it has on longer domestic flights from Newark to Los Angeles, he said, rather than the lie-flat beds it has on international routes. Ticket prices would cost roughly the same as a current business class fare, and hover around $5,000 and $10,000 for a round-trip itinerary, he said.

“You’ve got this convergence of technology,” he said, “that will allow us to make economic and profitable something that was not economic and profitable with the old technology.”

But some scientists and aerospace engineers are skeptical, pointing out that the claims plane-makers and airlines make sound promising, but are difficult to create.

Boyd, of the University of Colorado, said noise will be the biggest challenge. He notes that sonic booms could be less of an issue due to advances NASA has made on muffling the sound, but planes will still be able to fly at their maximum velocity only over water — making supersonic travel between cities in the United States difficult.

Meeting FAA and international noise regulations also will be difficult, he said. Supersonic aircraft require narrow, aerodynamic engines, experts said, but those are harder to keep quiet enough to meet government sound limits. Public debates on aircraft noise are also fraught with political issues, Boyd added.

“The inconvenience and discomfort of extra noisy aircraft just for a relatively small number of rich people, that doesn’t sound good,” he said. (Boom spokesperson Aubrey Scanlan said she’s “confident” the Overture will meet FAA regulations around noise.)

And Rutherford, of the International Council on Clean Transportation, said fuel costs will make it tough for supersonic air travel to become a viable business. Supersonic aircraft will burn seven to nine times more fuel compared to normal “subsonic” aircraft, he said.

Rutherford added that companies like United and Boom are aware of that, and pledging to use sustainable aviation fuel. But the supply of sustainable fuel is limited and the cost is high — two to five times costlier than fossil jet fuel.

“That is honestly a dealbreaker, I would guess,” he said.