In the early years of the 21st century, startup companies tripped over one another to promise supersonic transport (aka SST) to the masses. If hype and hubris were jet fuel, we’d be flying from Los Angeles to London in two hours for $200 by now. Alas, one of the startups has gone bankrupt and another has lost its engine supplier. And, oh yes: a third has entered a self-imposed “quiet period” — an irony for a company claiming to have mitigated the sonic boom that undermined the commercial viability of the last generation of SSTs.

But plus ça change … Sonic booms accompany any vehicle traveling faster than the speed of sound (660 mph at 40,000 feet), which is why the Anglo-French Concorde was never allowed to fly over land in supersonic mode. Instead, the gorgeous, deltawinged aircraft spent 27 years mostly flying between New York or Washington and London or Paris, a jaunt it could cover in three hours compared with about seven for conventional jet airliners.

The Concorde was a nice treat for the wellheeled — a roundtrip ticket averaged $10,000 when $10K was considerably more valuable — and to see the lovely plane in flight or even just taxiing at Charles de Gaulle made my pulse race a bit. But it never penciled out, not even close.

Moreover, no one has explained how the new players will succeed where British, French and U.S. aerospace failed. (A proposed Boeing SST never got off the ground.) Fake it until you make it may work for a social media company, but for an aircraft manufacturer? Let’s not even talk about moving fast and breaking things.

“I’m amazed they can still find investors,” marveled Guillaume de Syon, an aviation historian at Albright College in Pennsylvania. “Let’s be optimistic. Say they pull off the demonstrator aircraft, and by a miracle, in 10 to 15 years, they actually produce a 40- or 50-seater. Even assuming that, where are they going to fly? Show us 100 places you can fly to without breaking every environmental and noise rule out there. Concorde was making expensive lemonade out of expensive lemons, and they succeeded. But it was almost at gunpoint for the glory of Britain and France.”

Supersonic Highwire Act

Supersonic flight dates to 1947 when Chuck Yeager — he of “the right stuff” — first exceeded the speed of sound in an experimental Bell X-1 dropped from the belly of a B-29 bomber. Just seven years later, British aircraft engineers began work on what would become the first supersonic transport, a commercial airliner capable of flying at 1,200 miles per hour. This at a time when the Douglas DC-3 (cruising speed 207 mph) was still in widespread use.

The British had led commercial aviation with the introduction of the de Havilland Comet, the world’s first jet airliner, in 1949, only to see that supremacy erased when structural failures grounded the innovative plane. In Supersonic (Airliner) Non-Sense, R. E. G. Davies described the decision to go forward with an SST as motivated in part by nationalist one-upmanship. Having ceded market leadership to the United States, Britain would leapfrog the 600-mph Boeing 707 with an airplane capable of twice that speed.

“The prevailing mood was to ‘press on, regardless,’ as this was Britain’s chance to lead the way again,” Davies wrote. “Any suggestions that a supersonic airliner might not be economic to operate were summarily dismissed or ignored as the outpourings of doubting Thomases.”

Sud Aviation (later known as Aerospatiale) of France joined with the British Aircraft Corporation to produce the 100-seat Concorde, which made its first flight in 1969. Commercial flights began in 1976. Many airlines placed options to buy in a market projected to reach 350 aircraft. But in the end, only 20 Concordes were ever built, including six non-commercial planes.

Air France and British Airways, the only carriers to fly Concorde for any length of time, never paid for the 14 jets delivered to them. “The $3 billion development costs were picked up by the British and French governments, i.e., by the uninformed taxpayers,” Davies wrote.

Operating costs and maintenance proved far higher than projections, while utilization was just one-fourth that of subsonic airliners. Concorde used as much fuel to cross the Atlantic as a 747 but carried one-fourth the number of passengers. To be profitable, airlines need to keep planes in the air as much as possible, yet the Concorde required 18 hours of maintenance for every hour flown. Both airlines, moreover, felt obliged to keep an extra Concorde on the ground on standby, lest repairs delay a booked flight.

Concorde’s would-be competitors were even less successful. The Russian Tupolev Tu- 144 began service on the 2,400-mile overland route between Moscow and Alma-Ata in November 1977, but it was withdrawn from passenger flights just seven months later after a pair of crashes. It continued cargo service until 1983.

In the United States, Boeing, supported with federal money, began taking orders for its 2707 SST in 1969, with a design projected to fly 250 to 300 passengers versus the Concorde’s 100 — and at Mach 3 (1,960 mph at 40,000 feet) while the Concorde flew at a pokey Mach 2.15. But Congress halted funding in 1971, and only a non-flying model was ever built.

The U.S. SST effort survived as long as it did owing to “market studies that ranged from mild misconception to ludicrous optimism,” Davies wrote. “Compiled by aircraft manufacturers’ planning departments, prestigious consultants and government agencies at a steady frequency throughout the 1960s, they all had one thing in common. They were textbook essays in misinformation.”

On July 25, 2000, Air France Flight 4590 crashed shortly after take-off with all 109 occupants and four people on the ground killed, the only fatal incident involving the Concorde. Commercial service was suspended until November 2001, and Concorde retired in 2003 after 27 years of commercial operations.

that was then and this is something else

One change since Concorde’s heyday is that the folks/corporations who could afford it now often own their own jets or have access to them through fractional ownership providers like NetJets. The first new SST venture out of the gate — perhaps not surprisingly also the first to fail — was Aerion Supersonic, which launched in 2002 with a proposed supersonic business jet, the Mach 1.4 AS2 (target price $120 million). Though notably slower than the Concorde, the AS2 would have been faster than today’s premier CEO toys, the Gulfstream G600 (Mach 0.9) and the Dassault Falcon 8X (Mach 0.8).

For a time, Aerion looked most likely to succeed, with advance orders from both Net- Jets and FlexJet. But the company churned through partners, including Airbus, Lockheed Martin and Boeing. The AS2 went through multiple redesigns, from two engines to three, from a delta wing à la Concorde to a thin wing and horizontal stabilizer with moderately swept leading edges, purported to reduce drag. Though Aerion initially designed the AS2 for Pratt & Whitney engines, the company shifted to GE Aviation. And when Aerion declared bankruptcy in 2021, it owed GE $32 million.

Also targeting the corporate jet market is Spike Aerospace, with a proposed 12- to 18- seat Mach 1.6 airplane to be priced above $100 million. One novel feature of the Spike S-512 is its windows, or rather lack of them. It will use LCD screens to display the view, entertainment and, presumably, spreadsheets. Spike is claiming to have all but eliminated the sonic boom, with a sonic signature expected to be less than 75 PLdb (perceived loudness level) at ground level, sounding like a soft clap or muted background noise.

How is this achieved? I have no clue. Spike declined to answer my questions, instead providing a polite email demurral from CEO Max Kachoria: “Developing a supersonic aircraft will take years of engineering, testing and certification. We have taken on the slogan ‘It’s good to be quiet’ rather than issuing constant press releases about timing, funding or customers. In that sense, we are operating in a semi-stealth mode where what we are doing is well known but the specifics are reserved for our key stakeholders.”

Blake Sholl, CEO of the audaciously named Boom Supersonic, also declined an interview request. But he has been plenty talkative in the past, trumpeting orders from United, American and Japan Airlines for the 65- to 80-seat Overture. He’s been a bit quiet since Rolls-Royce announced in August that it was dropping out as Boom’s engine partner. Nevertheless, he told the Financial Times that “there’s a need for hundreds, if not thousands of these aeroplanes,” echoing the rosy predictions for Concorde sales five decades ago.

But that same article quoted Kevin Michaels, managing director of AeroDynamic Advisory consultants in Michigan, who said that Overture “is a paper aeroplane right now,” with “so many issues for Boom to overcome. I don’t expect to see it.” Since it was founded in 2014, Boom has raised $600 million from investors, Scholl told the FT, which noted that the company will need billions more to complete the airplane. Rolls-Royce made the engines for Concorde and has powered many military and civilian aircraft, so analysts say its departure is a red flag for Boom.

“The most cynical case for what Boom is doing is there’s actually a better business case to pretend to have an engine than to actually pay for one,” said Dan Rutherford, aviation program director at the International Council on Clean Transportation. “The more generous term for ‘fake it ’til you make it’ is ‘minimum viable product.’ Boom has said Overture will be that, and then they’ll have a second and a third generation. But that’s a fundamental misunderstanding of how aircraft are made,” he said. “It might work for a scooter.”

Why can’t we have new SSTSs?

The Concorde was built in the era of dial-up telephones and cars with carburetors. Today we drive electric vehicles (or they drive themselves, almost) and carry smartphones that each have more computing power than the sum total available to all the SST engineers back in the day. You might think that making a viable new SST would be, if not exactly child’s play, at least feasible. You might be wrong.

The issues facing EV development were all in the realm of engineering, while the challenges facing would-be SST producers require breakthrough science. The original Tesla Roadster used lithium-ion batteries developed for laptop computers, a carbon-fiber and aluminum body/chassis produced by

Lotus Cars, and a transmission sourced from BorgWarner. While integrating these elements in a brand-new automobile was impressive, it was hardly rocket science.

But that’s where SST development resides. Let’s start with the most obvious issue, the sonic boom, which readers of a certain age may have experienced back when fighter jets were allowed to go supersonic near populated areas. It’s a bit like a thunderclap, so incredibly loud that you feel it as much as hear it. Sonic booms break windows, and contrary to popular thought, they occur not only as the plane initially breaks the sound barrier, but all along its supersonic flight path. Nor does flying higher lower the noise level much, as was thought in the late 1950s.

“My first thought was, ‘Did somebody solve the sonic boom problem and not tell me?’” quipped Janet Bednarek, an aviation historian at the University of Dayton. “Even the Boom plane was only going to fly supersonic over water. It was going to have many of the same limitations as Concorde, and it wasn’t even going to fly as fast as Concorde.”

Braniff Airlines briefly flew the Concorde in the U.S., though only at subsonic speeds, delivering passengers from Dallas to Washington D.C., where an Air France or British Airways crew would take over for the trans- Atlantic flight. Concorde was also available for private charter, for a suitable sum.

“Back in the early ’80s, the person who founded Godfather’s Pizza, Willy Theisen, leased the Concorde to take him, his wife and 98 of their besties to London,” Bednarek recalls. “So the Concorde flew into Omaha. What I remember the most was how incredibly loud it was,” she said. “It takes a tremendous amount of energy to get a plane to go supersonic. I’m guessing they could make them somewhat quieter. But given the public’s sensitivity to noise, I’m wondering where could this thing fly. I’m guessing that’s why Rolls-Royce pulled out.”

According to the ICCT, “It’s harder for supersonic aircraft to meet subsonic noise standards because they require high-thrust, low-bypass-ratio engines that are louder in landing and takeoff.” The aircraft could double the area around airports exposed to substantial noise pollution compared to existing subsonic aircraft of the same size. While the U.S. could, in theory, set a weak domestic noise standard for SSTs to promote the industry, the ban on supersonic operations of civil aircraft over land in most parts of the world would limit the potential market.

The ICCT also estimated that the most likely configuration of a representative SST would exceed current emissions limits for nitrogen oxides and CO2 by 40 percent and 70 percent, respectively. The plane was estimated to burn five to seven times as much fuel per passenger as subsonic aircraft on representative routes. The SST model burned three times as much fuel per business-class passenger relative to recently certificated subsonic aircraft; in the worst case, it burned nine times as much fuel compared to an economy-class passenger on a subsonic flight.

Boom’s press materials say the company will achieve net-zero carbon emissions by powering its manufacturing site with renewables and flying its aircraft on 100 percent sustainable aviation fuel. While SAF is real, it is very scarce and expensive and will remain so for some time to come. If all goes well, SAF could meet 5 percent of global jet fuel demand by 2030, according to BloombergNEF, at a $1.50 per gallon premium over renewable diesel. But that’s a best-case scenario. And anyway, would it make sense for carriers intent on reducing emissions to use their cleanest and most expensive fuel in their thirstiest aircraft?

“Given existing noise restrictions and the incremental SAF costs, is there a market? No,” opined Rutherford. “I’m skeptical about how real those orders are,” he said, noting that both United and JAL’s orders came through their venture capital groups and the American order was conveniently timed for the Farnborough Airshow. “What’s the probability that this plane will be built? I can’t say zero, because of the Pentagon. The one way I see this going forward is the military takes an interest and just puts up the money.”

Let Uncle pay for it

Actually, the military already has. In July at the Farnborough Airshow trade exhibition in the UK, Boom announced a three-year strategic partnership with the United States Air Force valued at up to $60 million. The deal came through the Air Force’s innovation arm, AFWERX, and its AFVentures division. Known as the Strategic Funding Increase, the contract awarded to Boom coincided with an announcement that the company would collaborate with Northrop Grumman on a “supersonic special-mission aircraft,” based on the Overture transport.

Boom unveiled the XB-1, a one-thirdscale demonstration plane, in the summer of 2020, and said it would begin flight-testing the following year. The Boom website displayed photos of former astronauts and other NASA veterans hired as test pilots. In May 2022, the plane was reportedly 80 percent through pre-flight testing and due to fly by the end of the year. But as of December 2022, it had yet to leave the ground.

NASA has its own new supersonic, the X-59, built at Lockheed Martin’s Skunk Works in Palmdale, California. A part of the Quesst program, the X-59 is intended to demonstrate technology that reduces the loudness of a sonic boom to a gentle thump for people on the ground. The idea is to fly the X-59 over select U.S. communities to gather data for regulators on human responses to the sound generated. But it hasn’t flown yet either.

Concorde was still in regular service when development began on a next-generation aircraft that would have been far faster. As Davies wrote, “the lunatic fringe of the aircraft indust r end s Second Quarter 2023 11 try, the hungry industrial consulting firms, and the publicity-seeking airlines began in the 1980s to promote the Hypersonic Transport, or HST, with every meretricious argument they could lay their hands on to mesmerize the eagerly gullible media.” Nicknamed “The Orient Express,” the HST promised a three-hour flight time from New York to Tokyo.

NASA officials described a joint NASA/industry high speed research program as “a $2 billion down payment,” while Boeing and Douglas, dutifully followed by Aerospatiale, confidently projected a market for 500 to 1,000 aircraft by 2020. Davies railed against these assumptions in a letter to the editor of Aviation Week, which to his surprise led the section in January 1995. He referred to Boeing’s “realms of fantasy” and to the billions of dollars “to be extracted from taxpayers’ pockets.”

Davies’ letter drew little comment, and he died in 2011 after a 60-year career in aviation, including positions at British European Airways, Bristol Aircraft, de Havilland and Douglas, and 30 years as the Curator of Air Transport at the Smithsonian Institution. He never saw a successor to the Concorde take flight, but neither has anyone else.

If You Could, Should You?

Much has changed since the new SST companies received their seed funding. Flightshaming became a thing after Greta Thunberg’s speech at the 2019 UN Climate Action Summit. Covid-19 showed that many business meetings could be

And we seem to have reached the end of an era of ultra-low interest rates that allowed people to raise capital to fund really stupid ideas.

Even if there is a viable market for 50 or 100 supersonic jets — a big if — the cultural moment for them may have passed. “There’s a kind of that euphoria that comes with free money, and it’s not there anymore,” said Bednarek of the University of Dayton. “People who would have taken advantage of this are beginning to realize it’s not good business politics to be associated with a loud, fuel-guzzling, glamorous airplane,” she said. “It’s just not a good look.”