See what’s fueling the return of supersonic passenger flights


In January, more than 100 people gathered at an airplane hangar in California to watch NASA unveil its X-59 demonstrator jet — a futuristic aircraft designed to travel faster than the speed of sound that has helped revive excitement for supersonic travel.

There hasn’t been a commercial supersonic passenger jet since the Concorde stopped flying in 2003. Since then, supersonic jets — which travel faster than the speed of sound — have been used primarily by the military. But the space agency’s unveiling of the X-59, designed and built in partnership with Lockheed Martin, comes as a growing number of private companies are vying to bring back supersonic travel for the commercial market.

NASA’s single seat X-59 aircraft is supposed to produce a barely audible “sonic thump” to people on the ground. (Video: NASA)

Boom, Exosonic and Spike are among the companies promising modern supersonic travel that will be quieter, greener and more affordable than in the past. And at least one company — Hermeus — is exploring hypersonic flights, which would whisk passengers from New York to London in 90 minutes. But there are questions about whether these companies can make good on their claims given the economics of air travel and growing concerns about the impact of commercial aviation on the environment.

Here are five things to know about the effort to revive supersonic travel.

1. The sonic ‘boom’ could become a ‘soft thump’

NASA’s goal in developing the X-59 is to reduce the sonic boom — the thunder clap that resonates far and wide when an aircraft crosses the sound barrier. NASA scientists hope the demonstrator jet can prove that travel at supersonic speeds is possible without such earsplitting noise.

One key to quieting the boom comes from the plane’s design. The engine is mounted on top. The plane has a long, narrow nose and sculpted wing to help ensure the shock waves it creates as it speeds through the air are similar in strength and evenly spaced along the aircraft to create a gradual increase in pressure instead of the rapid jump that creates the loud bang, said Peter Coen, mission integration manager for the Quesst mission.

The sonic boom is around 105 PLdB, or perceived level of decibels, similar to that of the sound of a balloon popping next to you. In comparison, NASA says the X-59’s will sound closer to a car door slamming 20 feet away.

PLdB is one of the scales, in decibels, that is used to understand human response to sounds. (Video: The Washington Post)

Turning the boom into a “soft thump,” as NASA hopes, could also improve the economics for commercial supersonic flights. It could mean an end to the U.S. ban on supersonic travel over land, which was enacted over noise concerns. That in turn could make commercial supersonic travel financially viable because airlines would be able to fly supersonic planes to more destinations.

Designing and building the X-59 took roughly five years. Testing is underway, and other phases of the project are expected to take another four. The total projected cost is $839 million, according to NASA.

2. There’s a flurry of interest from private companies

Nearly a half a dozen companies are competing to be the first to offer supersonic travel to the public — a curious interest at a time when much investment and innovation in transportation is focused on developing cleaner, more climate-friendly options that consume less fuel or alternative propulsion technologies such as batteries or hydrogen.

Denver-based Boom Supersonic is eyeing 2029 for the debut of its supersonic passenger jet, called Overture. The aircraft is expected to seat 64 to 80 passengers, according to Blake Scholl, the company’s chief executive. It will travel at Mach 1.7, or 1.7 times the speed of sound — more than twice as fast as a regular passenger airplane.

Exosonic is one of the companies striving to bring back quieter, greener and more affordable supersonic travel. (Video: Exosonic)

One company, Aerion — which had backing from major players in the industry including Boeing and Lockheed Martin to build a supersonic business jet — has already bowed out of the race. It shut down in 2021, unable to secure the funding to continue it work.

Industry analysts say venture capital and the mind-set that commercial supersonic sounds like a good idea has largely fueled the revival.

“It’s that Silicon Valley mentality that you put money down on 20 things for one that does well,” said Richard Aboulafia, managing director at AeroDynamic Advisory. “Again, it sounds like a good idea. There’s a good market for air transport and people want to fly fast. We had Concorde in the past so it sounds right — so let’s put some money there.”

Bruce McClelland, a senior contributing analyst at aerospace and defense industry analysis firm the Teal Group, added, “A lot of projects attract money whether they’re completely viable or not.”

3. It promises sustainability

Companies say their new generation of supersonic jets will have a smaller carbon footprint, mostly because they will be fueled by sustainable aviation fuel. This is fuel is made from agricultural products including soybeans and animal fat.

But critics say that pledge ignores some significant realities. For instance, there isn’t enough sustainable aviation fuel for planes that exist today. The sustainable aviation fuel that does exist is more expensive — by some estimates two to four times the cost of fossil fuel.

And no matter the fuel, the reality is supersonic jets will always use more of it. According to a 2022 study by International Council on Clean Transportation, supersonic jets could use seven to nine times as much fuel as regular commercial aircraft while carrying fewer passengers. But NASA’s Coen contends that supersonic travel at least initially will be a very small part of overall CO2 emissions and a very small part of commercial aviation.

Even so, with airlines pledging to reach net-zero carbon emissions by 2050, some say it’s hard to understand how supersonic jets fit into that framework.

4. It could be affordable for more people

The Concorde ended service because only a small slice of the flying public could ever afford a ticket, among other reasons, including a 2000 crash that killed 113 people and grounded Concorde’s supersonic planes for a year. But today’s entrepreneurs say supersonic travel can be affordable — though maybe not at first.

They point to Tesla and the burgeoning space tourism sector as an example of new modes of transportation that have and could eventually become accessible to a growing segment of the population.

Analysts have their doubts, though, given how difficult it is for commercial airlines to stay afloat. Supersonic jets will carry fewer passengers and consume greater quantities of fuel. If that fuel is sustainable aviation fuel, those costs increase even more.

“Essentially, the faster you fly, the more fuel you are burning per mile,” said Iain Boyd, director of the Center for National Security Initiatives at the University of Colorado at Boulder. “Supersonic is always going to be more expensive.”

5. It could get even faster

Hermeus, based in Atlanta is just one of the companies exploring the possibility of a an even faster, hypersonic commercial passenger jet. While supersonic aircraft travel faster than the speed of sound, hypersonic aircraft travel at speeds five times faster or more.

Translated: that would make a flight between New York and London — a 90-minute trip — about the same as flying from New York to D.C. on today’s commercial aircraft.

The company’s Halcyon jet would travel at Mach 5 — or five times the speed of sound. A.J. Piplica, the company’s chief executive, said the company is laying the groundwork for Halcyon by building hypersonic drones that could be used for defense and national security purposes.

Hermeus’s Halycon promises to cut flight times between New York and London to a 90-minute trip. (Video: Hermeus)

But the company is open about the technological challenges it faces developing such a fast aircraft. Today, there’s a less than 50 percent chance of getting Halcyon in the air, Piplica says — but he expects the odds to improve over time.

Even then, Hermeus — and all the start-ups — will have to convince the public to buy in and will have to grapple with growing concern about the impact of air travel on the environment. It could be a tall order.


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