The EON NXT-01.

The EON NXT-01.
Illustration: EON Aerospace

Last week, we delved into the history of supersonic passenger planes — how they were developed, when and where they flew, and ultimately, what killed them. We also enumerated the many challenges facing the future of faster-than-sound passenger travel: noise, fuel consumption, and potentially outrageous per-passenger costs.

Today, we look at the companies promising to bring back supersonic travel. They face immense challenges — like finding engines in a market that doesn’t currently cater to supersonic travel, kickstarting development of renewable aviation fuel, and finding a path to certification with the Federal Aviation Administration, which has never approved a supersonic passenger plane to fly over North America.

With the stakes laid out, it’s time for us to investigate the main players in the supersonic transit (SST) space today — the startups promising to build brand-new passenger planes capable of exceeding the speed of sound. Let’s see just how close they are to bringing air travel back to what was possible when the Concorde plied the skies.

SST Contender #1: EON Aerospace

Image for article titled When Will Supersonic Passenger Planes Come Back?

Illustration: EON Aerospace

EON Aerospace is the personal project of South African tech billionaire Priven Reddy. EON promises to develop a passenger plane capable of speeds as high as Mach 1.9 (1,254 mph), the NXT-01, aiming to take to the skies in 2029. The NXT-01 concept is a low-boom design — which, as we discussed last week, means this aircraft would not generate a sonic boom when traveling faster than the speed of sound, allowing it to fly over populated areas at supersonic speeds without disrupting the population below.

EON — whose website has an expired security certificate — offers no real explanation as to how it will solve any of the problems currently facing supersonic travel. The website states that the NXT-01 will feature the “world’s first ever safe-landing mechanism” and that the company is researching the “first-ever bladeless [engine] technology,” with no specifics on how either of these concepts work. I could not find any design specifications or development milestones, such as scale model wind-tunnel testing, for the NXT-01. The company did not respond to my emailed request for comment, and the contact phone number listed on the company’s site was disconnected. No orders appear to have been placed for the NXT-01.

SST Contender #2: Spike Aerospace

A rendering of the Spike S-512.

A rendering of the Spike S-512.
Image: Spike Aerospace

Next up is Spike Aerospace, a supersonic aviation startup founded in 2012, focuses on the niche of private air travel rather than commercial aviation. Its design is known as the S-512, a 12-to-18-seat low-boom plane that promises private-jet amenities with supersonic speed. The startup is aiming for a 2029 release date.

Spike Aerospace, which also did not respond to my request for comment, has very few specifics on its website. It promises the S-512 will offer “proprietary Quiet Supersonic Flight Technology” that will allow it to cruise at Mach 1.6 (1,056 mph) with a ground-level noise of only 75 decibels. (The Concorde’s sonic boom was 110 decibels, for comparison.) Spike Aerospace blog posts discussing the technology make no effort to explain how it works, beyond “shaping of the wing, fuselage, and tail.” The company apparently flew a small-scale subsonic test craft dubbed the SX-1.2 in late 2017. At that time, representatives said they expected to have a supersonic piloted test craft flying by late 2019, and the completed S-512 flying by 2022. At the time of this writing in late 2022, no piloted test craft appears to have flown, and no supersonic tests have ever been reported.

Another rendering of the Spike S-512.

Another rendering of the Spike S-512.
Illustration: Spike Aerospace

The startup has a similarly vague approach to engines. According to Reuters, in 2019 Spike Aerospace was in talks with both GE and Rolls-Royce to build engines for its SST; since then, both of those companies have publicly pulled out of the supersonic business, and Spike has not announced a replacement engine manufacturer. In a recent blog post titled “Who Will Make the Engines for Supersonic Flight,” Spike Aerospace CEO and founder Max Kachoria admits there is no manufacturer willing to do so at the moment. “Who ultimately supplies the engine will be unveiled in time, as will the successful aircraft company,” he writes.

While details are incredibly vague and the timeline has been moved repeatedly, you can still reserve an S-512 today, if you’re so inclined; it’s only supposed to set you back $100 million.

And let’s be real: Even the renders are lazy.

SST Contender #3: Exosonic

Image for article titled When Will Supersonic Passenger Planes Come Back?

Illustration: Exosonic

Exosonic, a startup launched in 2019 by a propulsion engineer from Lockheed Martin, is taking a slightly different path to supersonic passenger transport by developing a supersonic military drone first. Its supersonic passenger jet concept, however, is promised to be both a low-boom design and capable of Mach 1.9. Exosonic has even partnered with the U.S. Air Force’s Presidential and Executive Airlift Directorate to adapt its supersonic jet for use as a future Air Force One. Unlike most other companies, however, Exosonic has stated that 2029 is the earliest potential date its SST could hit the market, and the company has shied away from publishing release dates (or offering reservations to purchase supersonic aircraft) in its promotional materials.

So when I asked about the Exosonic SST, a company representative gave me quite an honest answer: the supersonic passenger jet is not the company’s near-term focus. Instead, the company is emphasizing its supersonic drone program, which has already received government funding. The UAV currently in the works is intended to be a low-boom design used primarily for combat training. Future generations of U.S. Air Force pilots could use Exosonic drones as stand-ins for high-speed adversary aircraft.

Exosonic supersonic drone

Exosonic supersonic drone
Illustration: Exosonic

Since Exosonic’s supersonic drone concept is roughly the size of a fighter jet, it should be easy for the company to power it using any of a number of fighter-jet engines currently on the market. Additionally, since the drone doesn’t require FAA certification for passenger use, as long as the Exosonic drone’s sonic boom is quiet enough to meet noise requirements for aircraft flying over populated areas, it could even enter domestic flight testing, like the Lockheed Martin/NASA X-59 low-boom jet that will soon perform flight tests over the continental U.S. The Exosonic drone design has already undergone physical wind tunnel testing and begun full-scale development for control-surface testing, and Exosonic plans to begin flight testing in the late 2020s.

Exosonic still has plans to develop its passenger airliner, eventually, but the company wants to build on lessons learned with the supersonic drone. An Exosonic spokesperson told me that experience from drone development, support, and maintenance will all be applicable to a future airliner. As for what could power the Exosonic SST, the company spokesperson stated it will use a low- to medium-bypass turbine, but it is “not currently focused on… airliner propulsion solutions,” given the amount of work going into the drone. As a result, it’ll likely be a while before the President — or anyone else — will be flying on an Exosonic passenger jet.

SST Contender #4: Boom Supersonic

The Boom Supersonic Overture

The Boom Supersonic Overture
Illustration: Boom Supersonic

Boom Supersonic launched in 2014 after its tech-industry founder saw the Concorde in a museum and decided to build a supersonic jet of his own. Ever since Aerion collapsed, Boom is the de facto front-runner in the SST startup realm. The company recently finalized its design for a Mach-1.7 capable passenger jet, the Overture, promising “fares comparable to today’s business class.” Boom has become the focus of lots of media attention in the SST sphere; both American Airlines and United Airlines have put down deposits on dozens of Overtures, which are promised to be in revenue service by 2029.

Boom is quite a bit different from the other companies attempting to build an SST. Unlike the Eon NXT-01, the Spike S-512, or the Aerion AS2, the Overture is not intended to be a low-boom design. While this would almost certainly limit it to transoceanic flights, it also makes for a much less complicated airplane to engineer and build. Indeed, the Overture’s current design — a tailless delta wing with four medium-bypass jet engines — was unveiled after extensive wind-tunnel testing and a reported 26 million hours of software simulations, making the concept seem a little more grounded in reality than some other contenders. Even more exciting, Boom has a supersonic single-seat test craft currently in the works, known as the XB-1.

The Boom XB-1 test plane.

The Boom XB-1 test plane.
Photo: Boom Supersonic

Unfortunately, Boom still faces an uphill battle. The XB-1 has been heavily delayed: it was initially supposed to fly in 2017, then 2019, then 2020, then 2021, then this year. When I asked the company when it plans to have the XB-1 airborne, a representative said the first flight will be next spring.

Despite Boom’s advanced position, the company doesn’t currently have an engine supplier for the Overture. In 2020, Rolls-Royce signed on to build an exclusive engine for the supersonic airliner, but suddenly withdrew from the agreement this summer. No other manufacturer has offered to provide Boom with a powerplant. When I asked the company directly about its propulsion plans, a spokesperson noted that a Pratt & Whitney executive had previously praised Boom’s business. The company representative added that Boom “remain[s] on track for our engine announcement before the end of the year,” but stopped short of mentioning any specific companies that might be in talks with Boom.

The specific details Boom has publicized have raised further questions about how, exactly, the company plans to dodge the unprofitable fate of the Concorde. The Overture’s conventional high-boom design means it can never be used in supersonic flight routes over the U.S. or most of Europe. Furthermore, the Overture has an anticipated range of 4,250 nautical miles; as SimpleFlying points out, this likely eliminates it from transpacific routes. (Boom Supersonic’s own website brags about how quickly a supersonic plane could fly from Los Angeles to Sydney, a route that would require adding 2,000 miles of range to the Overture.)

Unfortunately, even on the transatlantic routes the Overture could complete, the current design only seats a maximum of 88 passengers. Right now, the smallest planes plying the Atlantic routes (the Boeing 737 and Airbus A320) have nearly double that capacity.

While the Overture is intended to fly on 100-percent sustainable aviation fuel (SAF) for “net zero emissions,” that still doesn’t change the fact that, with a maximum of 88 passengers aboard, it will be burning vastly more fuel per seat than a comparable subsonic aircraft. When I asked a Boom representative how the Overture could be profitable, the rep claimed that “Overture will cost 75 percent less for airlines to operate than Concorde.” Boom has used that claim before, but has never provided an explanation of how it arrived at that number.

Image for article titled When Will Supersonic Passenger Planes Come Back?

Illustration: Boom Supersonic

Still, let’s take it at face value. Towards the end of that plane’s service life, British Airway’s fleet of seven Concordes cost the airline roughly a billion pounds per year to operate, an inflation-adjusted $2.2 billion. That’s $308 million per plane, per year, for aircraft that spent an average of 900 hours per year in the air. (The average subsonic commercial airliner flies 3,500 hours per year.) A Boeing 747, ancient as it is, costs less than $10 million per year to fly for 450 hours a year; even at double the cost, the thirsty 747 would be an order of magnitude cheaper to operate. British Airways also reported spending 57 hours on Concorde maintenance for every hour of flying, despite the extremely low flight-hours the Concordes racked up.

All of this meant the Concorde’s break-even cost per passenger was five times that of the antiquated 747. Even if the Overture is 75 percent more efficient than the Concorde, that still suggests it will be more expensive to operate per customer than even the least efficient quad-engine subsonic jets in the air today. Compared with modern fuel-efficient twin-engine jets like the 787 Dreamliner, the economic case for the Overture is difficult to envision.

The Return of the Concorde?

To say supersonic travel is an uphill battle is an understatement. An SST must battle physics, economics, and governments just to make it out of development. Eventually, those factors grounded the only two supersonic jets that successfully entered passenger service half a century ago.

Those two SST didn’t last very long faced with the fickle reality of commercial air travel. Can any of the recent crop of hopefuls succeed where past examples failed? That remains to be seen. Let’s hope they can at least find some engines.