Even if supersonic flight becomes cheaper via new fuels or propulsion, that doesn’t reset the baseline. The same advances (materials, engines, fuel handling, manufacturing) will also apply to subsonic aircraft, where the physics are already far more energy-efficient. So if supersonic gets “cheap,” traditional jets will get much cheaper. Airlines will always arbitrage toward the lowest energy-per-seat-km for most routes, and supersonic flight is structurally disadvantaged there (drag, noise, routing constraints).
Historically, faster transport doesn’t replace slower transport wholesale; it creates a premium tier while pushing the mass market down to a lower cost/energy equilibrium. Concorde didn’t kill widebodies, widebodies got cheaper. My intuition: supersonic may of course exist as a niche (time-sensitive, premium), but its biggest impact would be indirect, accelerating efficiency gains that make conventional aviation even more dominant and cheaper.
Here's why. LNG offers 2 main benefits. The first is the higher energy density (53.6 MJ/kg vs 43 MJ/kg, so 25% more [1]). Airplanes are subject to the rocket equation, even if they are not rockets. The rocket equation says that the mass of the fueled vehicle is the mass of the vehicle at the end of the trip times the exponential of delta-v divided by the exhaust velocity. For airplanes, it is not exhaust velocity, but "effective exhaust velocity", because they borrow a lot of reaction mass from the atmosphere (the air used as oxidizer, and more importantly, the bypass air). The effective exhaust velocity is very high for subsonic airplanes, and much lower for high supersonic airplanes. The delta-v for subsonic airplanes is lower than the delta-v for supersonic airplanes because of the lower drag (although not as much lower as one would expect, because they need a higher attack angle). Overall, the benefit from the high energy density LNG is much more pronounced for high supersonic jets.
The second benefit is the use of the cryogenic LNG to cool off the engine. For very high speed engines, this is huge. So huge that the famous (but never materialized) SABRE engine was supposed to use liquid hydrogen, which is stored at much lower temperatures.
The disadvantage of LNG is, surprisingly, not the need for cryogenic storage. It is the lower volumetric energy density. It is 22% lower than that of jet fuel. The rocket equation does not care about volumes, only about mass, but larger volumes means bigger airplanes, so more drag.
So, for subsonic airplanes the advantages of LNG are not all that important, while the bulkier tanks are a pretty big downside. For high supersonic jets, the advantages of LNG are so high that they simply open up possibilities that are not there with jet fuel. The fact that the LNG is cheaper is a nice thing to have, but it's really not that important, since the economics of high supersonic jets are more impacted by the construction cost and very high maintenance cost than by the fuel cost.
[1] https://en.wikipedia.org/wiki/Energy_density#Chemical_reacti...
Wikipedia lists LNG as 53.6 MJ/kg and 22.2 MJ/L and jet fuel as 43MJ/kg and 35MJ/L.
53.6 / 43 = 1.247
22.2 / 35 = 0.634
Energy density by mass is higher than jet fuel. But it is higher by less than jet fuel's energy density by volume is higher than LNG. And LNG requires heavier tanks.
So all in all, if it's not absolutely needed because of the cooling advantages, LNG can store less energy in the fuel tanks.
That's a second order effect from fuel being the primary cost, and thus the primary lever to either make more profit or improve competitivity.
If airlines could triple their profits by doubling their fuel burn they'd happily do that.
The ultra high altitudes of LEO satellites showcase the steelman example, traveling effortlessly through the vanishingly thin atmosphere at hypersonic speeds with extreme efficiency even though the fuel expenditure to get them there was high.
For more reasonable hypersonic travel, at 100k feet, the “wind” force at 3375mph is only as much as you would feel at 400 mph at sea level… so you can exert the force needed to fly at 400mph, but for that same energy you are going 3375mph.
Of course there is a lot of tech needed to take advantage of these efficiencies, but it’s not a matter of faster = less efficient. As for economies, a jet that can fly LA to NY in 70 minutes, with an hour of turn at each end, could make 10 trips a day, potentially cutting the number of aircraft needed to cover a given route or route rotation by a factor of 4.
Obviously this is not currently practical on so many levels, but there is nothing fundamentally stopping us from achieving that level of service, given enough knowledge and technical capability.
If we ever want to achieve that level of understanding and competence, we will have to work on it when it seems impractical. Remember, it was in a single persons lifetime between flying precariously in glorified kites and supersonic flight.
Separately, I wonder if a lot of the demand is also obviated by in-air wifi.
It's also a pathway to incremental decarbonizing of aviation. LNG releases less CO2 per unit energy than oil, and methane can be produced biologically or synthetically which offers a path to total (net) decarbonization.
https://repository.tudelft.nl/record/uuid:63b89022-ac68-426d...
Which still puts it behind the 787 let alone the generation that comes next.. But you aren't going to succeed at making any new inventory without every possible efficiency improvement to drive sales and retirement of older inventory.
JFK-London in 3 hours vs 6 is pretty tolerable if you’re more comfortable for the 6 hours. SFO to Shanghai in 7 hours vs 14 would be a lot more compelling but Concorde could not do transpacific range.
There's no real way to make that much time on a plane bearable even if you had a lie flat bed: that's just a ton of time in the air.
Australian international travel would be the premier market if you wanted to travel supersonic (also our coastal cities mean most departures could accelerate immediately).
Problem is broad market trends don't care about me personally. There have to be a lot of people like me with both sufficient injuries and sufficient money and there probably are not.
If that were true, we’d all be taking trains and boats everywhere. We aren’t.
By comparison, a boat would take 7-8 days. The disparity in time saved between supersonic and subsonic flight is pretty trivial in comparison to the time saved between a boat and a subsonic plane.
Right now, a cheap 7 hour each way round trip between NYC and London is ~500$.
Halve it to 3.5 hours each way with a supersonic plane, saving a total of 7 hours.
Now, the real question is then, what's one hour of your time worth to you or whoever is paying for your flight?
If improvements to subsonic aircrafts bring down the price to 200$ instead of $500, people would still be willing to pay 200$ + 7 * $HOURLY for a faster flight.
Even with a low-ish estimate of $HOURLY = 50, it would make sense to take the supersonic fight if the price was $500, which it could conceivably be brought down to, and the market has already validated to be willing to pay.
People who could perfecty afford a $2,000 plane ticket still fly with $400 ones (as long as they are within reasonable standards), for example because they have a desired budget for a given trip, and the expensive option would blow it away, so they don't mind the extra time.
Cutting it to 3.5 hours isn't a 50% overall decrease, because those 3.5 will turn into 6.5 of real time.
So the marginal value of faster flight goes down the shorter the trip is, and these supersonic airplanes can't do the super long Pacific flights because physics.
It's a much smaller niche than is often imagined. But it's still a niche, I guess.
Others may disagree, but I'd rather cut an hour from the flight than the entire commute/parking/security/airport waiting. (Assuming conditions on the actual plane were the same.)
My biggest dilemma is whether to sit in the aisle or window. The former you can get up whenever you want but are bumped by passers by and neighbors exiting the row. Versus being the one doing the disturbing.
And if you can afford business class - where supersonic would be priced - then I mean... The meals are restaurant quality and the full recline?! I hardly want to disembark! The biggest discomfort is the dry sinuses.
But in getting to/from the plane you are cattle moving through a logistical labyrinth with countless possibilities for something to go wrong.
Overall when I started traveling I loved all of it, exciting, new. Now I hate this part as a whole, necessary evil of wasted life to get what I actually want where I actually want.
it's the everything-else part of air travel that is fucking awful.
40+ minutes of security theater even with NEXUS and other fast-passes, lost bags, massive PITA airports, delays, and the hoards of dumb fuckin rubes who have no idea how to travel and need to haul their comically huge carry ons that somehow got through sizing + emotional support chihuahua -- a far cry from even the worst subways I've been on.
[1] https://www.whitehouse.gov/presidential-actions/2025/06/lead...
[2] https://www.govtech.com/transportation/bill-authorizing-supe...
I don't believe the economics for that will at all work out the way they are pitching, but it has no relation to how much supersonic makes sense for a domestic short haul.
Rory Sutherland commented that, insteading of spending billions on high speed trains, why not spend a few million on making the experience nicer. Better carriages, more staff, nicer stations.
Why would you pick a 3 hour flight?
2. Concorde rather infamously could barely make the transatlantic trip from New York to London, because supersonic flight is expensive. Boom's currently nonexistent aircraft is planned to have about the same range. Neither could make the flight from LA to Dubai, which is a distance close to double their maximum ranges.
There are flights between St Petersburg and Moscow. About 10 daily. It's about 1 hour. Together with everything you described, it's more like 4 hours. A high-speed train is also 4 hours. So the only people who choose to fly are those who have a connection or those who couldn't get a train ticket because those are always in high demand.
and later in the article:
> Remember, Concorde burned 52% of its fuel just taxiing down the runway.
Setting aside that these are completely different claims, the author does not cite this claim at all and it fails my personal gut check. Where is this information coming from?
Source: Air France Flight 4590 Accident Report states that the plane had 95 t of fuel on board when the aircraft started out and used 800 kilos of fuel during taxiing (page 17) and 200 kilos after taxiing before takeoff (page 159). https://www.faa.gov/sites/faa.gov/files/2022-11/Concorde_Acc...
(Since there's a bunch of discussion about how to reduce taxiing consumption, I'll point out that one tonne of aviation fuel is about $700, so there's not much money to be saved by creating battery-powered tugs or whatnot.)
As far as takeoff, "at the start of cruise 20% of the total fuel burnoff will have been consumed while only 9% of the total distance will have been covered." From "Operation Experience on Concorde", a paper by the Design Director. While 20% is a lot, it is much less than 52%. https://www.icas.org/icas_archive/ICAS1976/Page%20563.pdf
Probably the biggest win in aviation emissions would be converting all the ground support vehicles to electric. They’re currently classified as off-road vehicles, so don’t have to adhere to the same emission standards and normal cars and trucks. Additionally, they already spend a lot of time parked at the gate, which makes charging convenient and means that workers are never “waiting” for the vehicle to charge.
Checking various links on taxiing burn yields about 2 tonnes which is a lot more realistic and reasonable (a previous HN comment indicates the 767 burns about a tonne taxiing: https://news.ycombinator.com/item?id=24283386 concorde burning twice that sounds fair)
The OP might have gotten confused reading articles like https://simpleflying.com/concorde-fuel-consumption/ stating concorde burned half its tank from the gate to cruise (mach 2 at FL600)
This seems incredibly inefficient. Is there a future for hybrid aircraft, which would feature both traditional turbofans and large batteries for energy storage?
Batteries would eliminate the need for an APU and power the aircraft during taxi, allowing the engines to be started just before actual takeoff, and shut down immediately after landing.
Either the batteries could power wheel motors directly during taxi, or the aircraft could mix turbofans with e-fans (which could also allow energy recovery during descent and help power the aircraft during cruise, reducing fuel consumption further).
> .. my recent trip from Abu Dhabi to LA. 24 hours door-to-door. We have the technology to reduce that to under 10.
The direct flight (by Emirates) takes 16h15 mins, so that leaves 7h45 mins not in flight. If we want to bring that down to 10 hours just by making the flight supersonic then that would require a flight time of 2h15, corresponding to a (ridiculous) speed well over Mach 4.
(I must admit I was more curious about Astro Mechanica's engine tech before they also threw in the intention to operate Uber for business jets...)
Obviously the real problem with this idea is environmental: emissions would be substantial and nobody wants an extremely noisy rocket port near their city.
Takeoff and climb / accel to Mach 1.7 was done with re-heat (afterburners), which did use a lot of fuel. After that, normal power (no re-heat) was used to get to Mach 2.0 and cruising (supercruise).
They did burn a crazy amount of fuel on getting up to supersonic speeds though.
(I was curious if there was any opportunity for some sort of system to power take-off from the ground, be it catapults like on air craft carriers or just power-transmission for electric planes, and the numbers I found were that while a surprising amount of fuel was used by the time the plane lifted off, it was more like 5% than 50%.)
The whole post comes off a bit as someone who doesn't really understand the passenger air travel industry very well, and isn't particularly interested in changing that.
But in practice, what happened with semiconductors is the exception, not the rule.
We are still often making wild predictions about the future of technology based on some kind of exponential take-off, it may turn out to be a lot more constrained by physics and energy density.
Supersonic commercial air transport is one such technology, possible and proven, yet not viable.
Mars colonies or interstellar travel could be in a similar bucket.
I really don't believe this. Even the Boom website says that most of these are "options" to purchase, but I'm guessing the "firm" orders are basically just non-binding letters of intent that effectively say "Sure, if you build it with these specs, we'll buy some at price X. Unless we change our mind."
And I'm further guessing that the terms include dates that Boom has zero chance of hitting. The author estimates that these won't be in commercial service before 2033, but I think that's still optimistic. My understanding (could be wrong, not an expert) is that new regular airliners take many billions and 10+ years to design, build, and certify, and that's without the complications of supersonic and brand new engine designs.
The Boom stories have been circulating on HN for a decade now [1], and they originally were claiming two years to have a manned prototype, which was obviously untrue. I guess they are like the Tesla of the sky in that regard.
I struggle to imagine this is a very efficient design, that something designed for going mach 1.something breathing significant air is ideally suited for being at sea level not moving running a generator. Just feels like the stupid timeline having it laughs at us all again. https://boomsupersonic.com/press-release/boom-supersonic-to-...
Update: also, I was surprised in the first place because I thought the big challenge for boom was they were trying & failing to get engines. They eventually got Kratos to sign up but I thought it'd mostly be a Kratos engine... https://ir.kratosdefense.com/news-releases/news-release-deta...
Those who could easily afford supersonic can already afford other luxuries; the only one it gives is time; but if time is of the essence you can save it elsewhere by chartering your own jet.
Honestly, this seems like the place to start with supersonic technology. The very wealthy are price-insensitive and would be ok paying 3-4x as much to get somewhere 2x faster. A good place to prove the technology, infrastructure, and market opportunity before cost-optimizing to try to get interest from mass-market travellers.
I travel each year to see family abroad, a minimum 2-leg trip totaling at least 27 hours. I can't sleep on planes so I arrive exhausted and am useless and cranky for the first 2 days after this trip. I would happily pay 2x the fare to cut that trip in half.
The idea that such progress could ever falter is anathema to such a cohort (which, in their defense, have lived their whole lives in the most technologically anomalous period of the entirety of human history), making them susceptible to scams like Boom.
Instead, I'd implore people to consider that true progress is the ability to do more with less, and not merely the ability to do more with more.
Being able to do more with less is equivalent to being able to do much more with only little more.
Just look at the whole circus around the hyperloop instead of just building high speed trains.
You are not the only consumer of air travel. Supersonic is not for you, it is for elites willing to spend 4x the ticket price for half the flight time. Concorde tickets were $6000 for D.C. to London in the mid 1990s, so about $12,500 today, and that was for an economy-style seat. It was very popular among a certain segment.
East Coast US to Europe in 3-4 hours versus 7-8, West Coast US to Asia in 5-6 hours versus 10-12.... makes it more like a domestic flight.
Of course the disadvantage, is no more air service for non-business class customers (that being most of us).
Meaning a big price increase for us normal passengers?
And yes, I know flying only makes roughly 5% of world emissions. It also turns out that these are some of the most avoidable emissions. We should be cutting them first.
And if you point that out, you get downvoted to invisibility on Hacker News and elsewhere.
Because the technologies we had were good enough. It turned out that very few people needed to cross an ocean in three hours instead of six hours. On my way to this conference, I flew from Switzerland to San Francisco. It took eleven hours and cost me around a thousand dollars. It was a long flight and kind of uncomfortable and boring. But I crossed the planet in half a day!
Being able to get anywhere in the world in a day is really good enough. We complain about air travel but consider that for a couple of thousand dollars, you can go anywhere, overnight.
The people designing the planes of tomorrow got so caught up in the technology that they forgot to ask the very important question, “what are we building this for?”
Transpacific flights from California have no sonic boom population issues for 90% of the flight, and there’s already a large market of people spending $10k on business travel.
Reducing travel time from 12hrs to 4hrs would be a product with a lot more demand than 7hrs to 3hrs to Europe.
Since hearing that, I see the effect in other areas of life, and transportation is one. I travel differently when the flight is 3 hours as opposed to 7 or more. Shorter trips, less luggage, less advance planning, less exhaustion, etc.
At first it will be available only at a premium, but that's how innovation usually goes. When the market finds something people love, capital seeks opportunities to lower the cost and increase the quantity. The real price of travel by aviation has declined dramatically over the last 50 years, for example.
I've got friends and family all over the world... I would for sure go visit more often if it wasn't so darn long just to get there and back.
In an interview with CNBC Mr. Scholl talked about this pivot [2].
1. https://boomsupersonic.com/press-release/boom-supersonic-to-... 2. https://www.youtube.com/watch?v=ELl2uUAfGBw
What is this? I can't find easily the meaning of "bits to atoms." Is this meaning that US is going away from digital "exports"?
Never heard before either so you're not alone.
EDIT: the reference to America is, again I assume, the trend to bring manufacturing back to the US from mainly China.
What does that end up doing to the cost of a seat in coach?
That said, it might still be flying if its recertification flight hadn't happened on 9/11.
Jet fuel cost about $1/gallon when Concorde retired. Five years later, it would hit $3/gallon. I have to imagine that would have ended it if nothing else had by that point.
Nice (misleading) buried lede re: Boeing I suppose.
I'd love to be able to afford business or beyond but I honestly don't even want to try it because I know I won't want to go back.
So the environmental impact isn't even worth mentioning?
I think more and more people are having this experience. It's just not cheap enough yet, and hasn't penetrated the used market far enough yet. But I think it's just a matter of time.
That said the US used to have the space shuttle and that has gone the same way.
There is a proven middle ground, where you can pay the current price or x the price for 2x the speed.
> Blake’s pitch to airlines is enticing: “You’re already flying this route with a 300-seat plane where 80+ people in business class generate most of your profit. Give those passengers a supersonic plane, cut the flight time in half, and charge the same price.”
And now most of the profit for the 300-seater is gone. What does this do to flight pricing for those who were flying economy?
Some airlines "take" the marginal economy seat loss on larger planes because those are the ones they can fill with business class seats and make an even larger profit.
Even then it's a complex math on whether economy is hurting those flights' profit margins since those people buy things in-flight such as Wi-Fi and extra bags. Base fare is not the only way airlines make money.
What really kills this though is the value proposition for the business class passengers. I think I'd rather pay extra to sit in a comfortable seat for 16 hours, where wifi is now a standard feature, than cram into a smaller (likely noisier) seat for 8 hours. The cases where that 8 hours matters - especially when you can work from the seat if you have to - are fleetingly few. In the 70s, you couldn't do much in an airplane seat so it was wasted time. This is no longer the case and is steadily getting better.
I swear boom spends more on puff pieces than any other aerospace company. They continuously make claims they will do things by certain dates that are unrealistic.
They claim they will be delivering airplanes to United that would be in service in 2029:
https://boomsupersonic.com/united https://www.cnbc.com/2021/06/03/united-will-buy-15-ultrafast...
However new aircraft take 5-9 years to certify and they have not yet even built one! Not to mention new engines take a similar amount of time and they are supposedly building their own brand new engine, which is a substantially harder task.
Now they are claiming the first "test" flight will be in 3 years despite the fact that they still don't have a plane or an engine built. I hope someone over their let United know they are going to be a little late. Their website hasn't amended to article to say they were wrong.
I wonder if we can look to history to see how long it takes between when they say they will fly something and when it actually flies? Oh right, we can!
https://en.wikipedia.org/wiki/Boom_XB-1
"The original design was unveiled at Centennial Airport in Dove Valley, near Denver, Colorado, on November 15, 2016,[6] and it was initially intended to make its first subsonic flight in late 2017"
"The XB-1 performed its first flight test on March 22, 2024, flown by test pilot Bill Shoemaker from Mojave Air and Space Port.[1]"
They were only 7 years off but we all make mistakes.
Astro Mechanica
- LNG isn't used because weight needed for fuel tanks that will keep it cold enough to stay liquid cancels out any benefits. For anyone interested in a famous failure of a similar idea: https://en.wikipedia.org/wiki/Lockheed_CL-400_Suntan - I don't know what analysis they are doing that makes them think reducing the number of passengers and going to supersonic is possible while maintaining current ticket prices... but it's not. - Engine and plane makers are not allowed to run airlines. Anyone unfamiliar with the field can look up United Aircraft. - Their engine does sound like it's trying to do some cool things. I kinda suspect it's just a fun way to pass the time on the governments dime given all the other unrealistic stuff they are talking about though.
Hermeus
These folks are legit. Don't know if they will be successful but outsourcing the jet engine and focusing their work on the ramjet and the integration of the two makes alot of sense.
I wonder what's going on there?
> Translation: Building airplane engines is hard
There are many hints previous to that, but that gave it away for me. If I want LLM output I’ll request it from the model myself, thanks.
What is this even supposed to mean?
To me this comes across as "I'm not sure if you'll be impressed by a supersonic jet that can surpress sonic booms, so I shoehorned AI into the description to jazz it up." It makes me wonder why the author doesn't think the former is impressive enough on its own.
Spacex and blue origin has already demonstrated heavy payload transport, why can we just move to this than work on supersonic
Sorry can't help but chuckle at this....
there's thing we lost we i.e skills, grit, creativity we might never recover from
