One of the odd aspects of modern air travel is that it’s not really getting any faster. Ever since British Airways retired its money-losing supersonic Concorde in 2003, airlines have generally stuck to top speeds of around 615 miles per hour. That’ll get you from New York to San Francisco in five or six hours, depending on the winds, but you can’t find a plane that will get you there significantly sooner.

We’ve largely learned to tolerate our slow, boring aircraft. But there’s a compelling case that we shouldn’t — that air travel should actually be much, much quicker.

Right now there are a host of energetic startups and NASA engineers working on sleek new supersonic jets that could fly twice as fast as today’s commercial planes, if not faster. These jets would be major upgrades on the noisy, fuel-squandering Concordes of old, and they could be ready within the decade.

When you talk to people working on these super-fast planes, it’s hard not to get swept up in the excitement. Take Blake Scholl, the CEO of Boom, a startup that’s working with Virgin Galactic to put a new supersonic business jet into service by the early 2020s. He envisions a day when anyone could cross the Pacific or Atlantic in just a few short hours. “It changes how you think about the world,” he tells me.

“In aerospace, there are two great passions,” Scholl says. “You either want to build rockets and go colonize Mars — or you want to go really, really fast. People like Elon Musk are focused on the former. We’ve built a team that’s obsessed with the latter.”

So what’s the holdup? For some, it’s mostly politics. In a new paper for the Mercatus Center, titled “Make America Boom Again,” policy analysts Eli Dourado and Samuel Hammond make the case that outdated regulations are hindering innovation in air travel. Since 1973, the Federal Aviation Administration (FAA) has banned civilian aircraft from flying faster than sound over land, to avoid the house-rattling sonic booms that the Concorde used to make. Yet recent technological advances have enabled supersonic designs that don’t create loud booms. So why not replace the FAA’s blanket ban with a simple noise standard, and let supersonic travel flourish?

Yet there are also skeptics who argue that regulations aren’t the only thing holding back our supersonic future. In practice, faster air travel isn’t always worth it, and airlines have excellent reasons for preferring those slow, boring planes — from fuel efficiency to airport noise to concerns about climate change. “I wish them all the best!” says longtime aviation consultant Robert W. Mann Jr. of the push for supersonic flight. “But it’s still not clear that there will be a market for this.”

That is to say, there are two tricky questions to explore here: Can we actually bring back supersonic flight? And even if we can — should we?

The Concorde, revisited: Why early attempts at supersonic flight failed

Anyone who wants to build a supersonic plane today first has to grapple with the tragic failure of the Concorde jet, a joint venture between Britain and France that began carrying passengers in 1976.

The Concorde was a technical marvel, flying at at Mach 2 (twice the speed of sound, or 1,512 mph) to go from New York to London in just 3.5 hours, instead of the usual seven or eight. But it suffered its share of economic woes, and British Airways finally retired the jet in 2003:

The Concorde’s demise is a complicated tale, but it suffered from two mortal flaws. First, it was a horrendous fuel-guzzler and expensive to operate. Under the laws of physics, the air resistance or drag that a given object faces in flight increases rapidly as you approach Mach 1. So a plane flying supersonic requires a lot more energy than one flying below the speed of sound.

The Concorde’s designers tried to reduce drag by giving their plane a sleek body and short, slender delta wings. Even so, the Concorde required staggering amounts of fuel, burning roughly eight times as much oil per passenger mile for a trans-Atlantic trip as a modern-day 777. That made tickets forbiddingly expensive: $10,000 or more for a New York–London round trip. As oil prices rose, British Airways and Air France (which operated the jets) struggled to consistently fill the jets’ 100-125 seats. Bad for profits.

A second problem, meanwhile, is that whenever the Concorde traveled faster than the speed of sound — about 767 miles per hour — it created noisy sonic booms in its wake. To put it simply, the air in front of the Concorde couldn’t get out of its way fast enough, so it bunched up into large shock waves in a cone trailing the plane. Wherever those shock waves reached the ground below, they’d be heard as a loud “BANG, BANG” that could rattle windows, shake structures, and startle people.

Opposition quickly mounted, and in 1973 the FAA banned civilian aircraft from traveling at supersonic speeds over the United States. The Concorde could only exceed Mach 1 over water, limiting its market. British Airways and Air France mainly flew the Concorde out of New York and Washington DC to London and Paris, though there were a number of other international routes over the years.*

After the Concorde went bust, airlines shied away from supersonic flight. The extra speed didn’t seem to justify the hassle. At least, until recently.

How new technology could make supersonic flight viable again

Over the past decade, a number of aerospace engineers and entrepreneurs have been revisiting the Concorde’s demise. And some of them have walked away thinking that supersonic flight could work today — with just a few important (if difficult) tweaks.

A few years ago, Blake Scholl, a former coder and longtime amateur pilot, was messing around with spreadsheet models and realized that a number of recent advances in aerodynamics and engine technology could, in theory, allow engineers to build a plane that was far more fuel-efficient than the Concorde. “If you could do that, you could have a plane that was competitive with existing business travel,” he says. “I started running these numbers by various experts and realized it wasn’t just science fiction.”

In 2014, Scholl founded Boom, an aviation company based in Denver, Colorado. He has since assembled a team that includes accomplished former NASA, Boeing, and Lockheed Martin engineers to design a working successor to the Concorde.

They’re not alone. Back in 2002, a group of investors led by Robert Bass formed a company called Aerion that aimed to harness innovative new drag-reducing technology to create a much more efficient supersonic business jet. Aerion is pretty far along in this task: In 2014, the company announced a partnership with aerospace giant Airbus to build and certify a supersonic craft within the decade. (Gulfstream, an established jet manufacturer, is also working with NASA on its own designs for supersonic flight.)

The race is on.

So what makes these companies think they can do better than the Concorde’s designers and build a vastly more fuel-efficient plane? In interviews, Boom and Aerion pointed to three broad technical advances that make this all seem feasible:

First, modern-day computer modeling makes exploring new aircraft designs far easier than it was in the 1960s. If the Concorde’s designers wanted to test a new shape to see how it affected drag, they had to build a scale model and put it through large wind tunnels — a clumsy process that could take months. Nowadays, genetic algorithms can explore and tweak new shapes much more quickly and effectively. Newer composite materials, like carbon fiber, allow aircraft designers to pursue shapes and contours that weren’t possible for the Concorde’s designers, who worked with aluminum. (These materials can also better deal with the serious heat that builds up on the leading edge of the plane’s wing at speeds above Mach 2.) Today’s jet engines are far more efficient than they were in the Concorde’s heyday.

“The breakthrough will be in the sum of those parts, not any one invention,” Scholl says. Put those three factors together, and he thinks Boom can build a plane that goes at top speeds of Mach 2.2 while being 30 percent more fuel-efficient than the Concorde. It will still create sonic booms, though quieter than the Concorde’s.

The proof, of course, will be in the testing. Boom unveiled a design for its supersonic XB-1 jet in mid-November. The company will then team up with Virgin Galactic to build and test a prototype at Edwards Air Base in California by the end of 2017. The hope, Scholl says, is to have a working plane in service by “the early 2020s.”

Aerion, meanwhile, is pursuing a different design that harnesses supersonic natural laminar flow, a concept it developed (and tested with NASA) to reduce the turbulent airflow around wings and reduce drag. Aerion will work with Airbus on the engineering and is in the process of selecting suppliers to manufacture the engines. The plan, says spokesperson Jeff Miller, is to get its AS2 plane into service by 2024:

Assuming these planes work, the next challenge will be finding a market. Scholl’s goal is to introduce a plane that will cost just $5,000 to fly round-trip between, say, New York and London. At that price, his market research suggests, there will be enough business travelers willing to pay a premium for speed that he can fill small 45-seat jets. (As part of their deal, Virgin has an option to buy 10 of Boom’s planes.)

Consider the advantages: A flight between San Francisco and Tokyo might take just four hours instead of 11. A flight between New York and London, three instead of eight. “You could leave early in the morning from New York, have afternoon meetings in London, and be back home in time for dinner,” Scholl notes.

Still, it’s far from clear that Boom and Aerion can succeed in luring enough passengers to turn a profit. For one, notes Mann, the aviation consultant, their planes will still be less fuel-efficient than conventional planes, which means they could be more vulnerable to sharp swings in oil prices. Plus, there are market risks. The most profitable Concorde route lay between the great financial centers of New York and London. But what happens if, say, Brexit ends up shrinking the size of London’s banking industry?

“Obviously we’ll have to see,” says Mann. “But those are just examples of the sort of external shocks that could impinge on the practicality of supersonic travel.”

Boom and Aerion remain optimistic. The broader hope is that if supersonic flight gains a foothold with business travelers, costs will eventually come down as technology improves. Scholl’s ultimate goal is to make supersonic flight affordable to everyone. “It’s the same thing that Tesla did,” he says. “They started with the luxury Roadster and are now focused on mass-market cars.”

Because Boom and Aerion’s planes would only fly supersonic over water at the start, they could coexist with the FAA’s current ban on overland travel (although both companies could face regulatory hurdles around the noise their planes will make on takeoff and landing; more on that below).

That said, oceanic flights are still a relatively limited market. For supersonic travel to truly conquer the entire world, someone would have to take the next step and develop a plane that doesn’t produce terrifying sonic booms over land.

And that’s where NASA comes in.

The next big challenge: silencing sonic booms to allow overland flights

Ever since the 1970s, NASA has been wrestling with the math around the pressure waves that create aircraft sonic booms, trying to figure out how to reduce them. And, over the past decade, its engineers think they’ve finally cracked the problem.

“We’re at the point where we think we can design a quiet supersonic airplane,” says Peter Coen, the commercial supersonic technology project manager at NASA’s Langley Research Center. His team is currently working with Lockheed Martin on a $20 million project to design a prototype X-plane with much, much softer booms.

The science of what Coen’s team is doing gets a bit complicated (see this report for the gritty details), but here’s a very basic explanation. When a plane like the Concorde travels at supersonic speed, it creates a bunch of invisible shock waves, sharp pressure disturbances emanating from all the objects that stick out of the plane — the nose, the windshield, the wings, the tail. They’re shaped like this:

These shock waves are all different strengths, and they as they travel through the air, they coalesce into just two powerful waves — a strong positive pressure wave at the nose and a strong negative pressure wave at the tail. This “N-wave” configuration is highly stable and doesn’t decay much as it travels toward the ground. When this wave hits people below, our ears register it as two noisy bangs from each of the two sharp swings in pressure.

“So the trick,” Coen says, “is to keep those shock waves from coalescing into a N-shaped signal.” In theory, a plane with a different shape would create shock waves of more uniform strength that coalesce more gradually as they move through the air. If done successfully, people on the ground would experience a gentle rise in pressure when the wave hits rather than two sharp pressure changes.

Recent experiments have been promising. The Concorde created booms that were perceived to be as loud as 135 decibels on the ground — about as loud as the sound a jet engine makes from 100 feet away. But by experimenting with different shapes, NASA has developed aircraft models that, in wind-tunnel tests, create booms as soft as 79 perceived decibels, roughly comparable to a car passing 10 feet away. Eventually, NASA would like to get that down that to 70 decibels.

The goal is to design an actual plane using these concepts. Here is an artist’s conception of what the new X-plane might look like.

NASA will then plan to build a one-third-scale prototype and conduct the first test flight in 2020.* The idea is that they’ll gather data on what sorts of sonic booms the planes actually make, and then the FAA can use that data in deciding whether it makes sense to replace the blanket ban on overland supersonic travel with a noise standard — saying, for example, that supersonic flight is acceptable overland so long as the booms are below a certain threshold. (If that actually happened, Gulfstream says planes with quiet booms might be a possibility by 2025 or 2030 or so.)

But changing those rules will require wading into the murky world of politics — which is never easy.

The US government could still put the kibosh on supersonic flight

In theory, the FAA is open to the idea of revising its blanket ban on supersonic flight over land. In 2011, an FAA official gave a public presentation explaining that research on silencing sonic booms has progressed far enough that it may be time to consider a noise standard.

But the FAA is moving very slowly on revamping the rules — in part because it’s focused on other challenges, like overhauling the nation’s air traffic control system. The agency is also waiting for NASA and other companies to demonstrate their quiet-boom technology before crafting fresh regulations.

In their paper for the Mercatus Center, Dourado and Hammond argue that the FAA’s current approach is precisely backward. It would be much better for the agency to set guidelines ahead of time on what type of overland sonic booms would be acceptable — so that companies can have some certainty and know what to aim for in developing new designs. “Right now, the FAA is saying we’ll accept supersonic when we hear what’s acceptable,” says Hammond. “We’re trying to point out the absurdity in that.”

Even if the boom issue gets sorted out, however, there’s still another hurdle for supersonic planes: takeoff and landing. While all supersonic planes would fly at less-than-supersonic (or “subsonic”) speeds around airports, they’d still make a fair bit of noise on takeoff and landing. And that’s where things get a little tricky.

Over the years, the FAA has developed strict standards for the noise that airplanes can make around airports. Aircraft manufacturers have responded to these rules, in part, by doing things like building high-bypass engines with large-diameter fans that propel air out of the engine more slowly and hence reduce the noise from the exhaust.

The trade-off with these high-bypass engines is that they’re not as fuel-efficient at takeoff and the large fans create more drag while the plane’s in the air. That’s not a huge deal for normal aircraft, but it could be ruinous for supersonic jets. If the FAA requires supersonic jets to adhere to the newest, strictest noise standards coming into effect by 2018 (known as Stage 5 standards), those jets will take a major fuel efficiency hit. By contrast, if the FAA merely asked supersonic aircraft to adhere to the standards that were in place back in 2006 (known as Stage 3 standards), Scholl estimates, that would reduce supersonic ticket costs by some 15 percent.

Dourado and Hammond argue that the FAA should allow looser airport noise standards for supersonic jets in the very beginning, at least, to allow the technology to get to market. Engineers can then work on making them quieter. The companies making the supersonic planes agree. “The physics of supersonic flight are quite different. Saying you need to meet the standards of subsonic flight could put a damper on development.” says Aerion’s Miller. “We’re hoping to reach a compromise with the FAA on this, since we’re talking about a new industry that could be beneficial.”

This could prove a contentious subject, however. The politics around airport noise can be extremely dicey (in separate research, Dourado and Raymond Russell have found that most airport noise complaints to the FAA come from just a small handful of people). A strict airport noise rule wouldn’t kill supersonic flight — Aerion plans to certify the AS2 even if the rules don’t change — but it could increase prices and dampen the market, particularly in the early days.

The deeper question: Do we really want supersonic flight?

The noise issue raises a bigger philosophical question around supersonic flight: How much do we really value speed, anyway? After all, the structure of our current aviation industry is the result of a series of compromises around competing values. And over the past 30 years, airlines have shown that there are a lot of other things we value more than simply going really, really fast.

Back in the 1970s, Mann explains, the industry realized that if it wanted to keep growing, it needed to be a good neighbor. That meant replacing their existing fleet of loud and dirty airplanes with much quieter models — even if it meant some trade-offs in terms of performance. Similarly, ever since the oil shocks of that decade, the industry has made a point of valuing fuel efficiency over raw speed.

“The optimal cruise speed has basically declined over the years,” Mann says. “Above about Mach 0.8, you pay so much for that speed in terms of fuel.” Today, a flight from New York to Denver or from DC to Miami actually takes longer than it did in the 1970s — because airlines have realized that the fuel savings are worth the delay.

Going forward, there’s another important value to weigh on the scale: climate change. Aviation is already the fastest-growing source of greenhouse gas emissions in the world, and the world’s airlines just agreed to a sweeping deal under the International Civil Aviation Organization to offset the growth of their emissions starting in 2020. Conventional aircraft manufacturers have worked hard to reduce fuel burn by 45 percent since 1968, and companies like Boeing and Airbus are now pushing to cut fuel use even further, through the use of lighter materials and novel engine designs. Still, this remains one of the toughest sectors to decarbonize.

And new supersonic jets that burn fuel at higher rates than conventional planes seem to go in precisely the opposite direction — even if they do save travelers time. True, a few supersonic business jets flying around wouldn’t have a major impact on emissions. But if cheap supersonic flight became ubiquitous, the global warming impact could be staggering (particularly if the planes fly at higher altitudes, due to the contrail effect). With the world already struggling to avoid dangerously large temperature increases, a new fuel-inefficient plane seems like a luxury the planet can ill afford.

When I asked NASA’s Coen about the climate consequences of a world filled with supersonic jets, he agreed that it was a real concern. But he also pointed out that there might be ways to square these different values. Future caps on aviation emissions could, for instance, spur supersonic jets to adopt low-carbon biofuels. (Or there’s another way this could all go: As Mann pointed out, it’s possible that stricter carbon caps could simply make supersonic flight unviable.)

It’s still too early to say how these issues will play out, but it’s a good reminder that our slow, boring planes have quite a few things going for them.

Even so, at the end of the day, the prospect of faster flight will remain forever tantalizing. The reduction in travel times has been one of the great technological breakthroughs of the past 200 years. This isn’t merely convenient; in some ways, it’s been the very marker of progress. Humans have long been obsessed with breaking new barriers, with going faster and faster. Even if on a purely romantic level, it would be a shame if we’re currently stuck going about as fast as we’ll ever go.

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* Correction: I originally wrote that NASA and Lockheed Martin are working together to build a prototype of a quiet supersonic plane. That’s not quite accurate. Lockheed Martin has a contract to design a plane. But NASA hasn’t yet selected a company to actually build the prototype.

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