I just don't see any pressing need for supersonic jet travel now that in-flight Wi-Fi, hi-res HMDs for your laptop and the Nintendo Switch all exist. And I think that trying to justify it in terms of "we have to end the stagnation and go back to a regime where plane speeds increase YoY" is silly: either it provides a compelling service for its high cost (there's no getting around that air drag and fuel consumption increases quadratically with speed) or it doesn't, and personally I don't think it will.
The Russian Tu-144 first went supersonic on 5 June 1969, four months before Concorde, and on 26 May 1970 became the world's first commercial transport to exceed Mach 2
> Concorde burned 52% of its fuel just taxiing and taking off
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?
It seems like there's not enough interrogation of how much time supersonic could actually save you. 3 hours of flying from LA to Seattle, 2.5 with climb and approach removed. If you cut it in half, 1h15m saved. On the flip side, how long does it take to get to the airport, park, though security, board, deboard, massive buffer time because flights are expensive and you don't know what might delay you, god forbid you have baggage to check and pick up. Flying at twice the speed might reduce the time to fly by less than 20%. Taking small on-demand supersonic flights from regional airports as suggested is definitely not a solution btw, because it's a pipe dream.
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.
Notably Boom's big pivot a month ago was to start selling their supersonic designed engines to data centers for power.
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...
Equating speed of travel with innovation is lame: a lot of work has been done in recent decades on making airplane engines more efficient, which makes air travel more economical both in terms of cost as well as C02e emissions per passenger (the Jevons paradox implications of that can be taken as read).
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.
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?”
> 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.
What does that end up doing to the cost of a seat in coach?
Regarding the “supersonic is now viable because LNG” argument, but for a different reason than usual.
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.
That is not quite true. The advantages of LNG are much more important for high supersonic jets (Mach 2.5 and higher) than for subsonic jets. There are disadvantages too, and they are quite significant for all jets, but altogether the tradeoff is worth it at high speed long endurance supersonic jets.
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.
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.
You are absolutely right. My 22% was a mistake, the correct number is indeed 36.5% lower volumetric energy density. But that strengthens my argument, doesn't it?
> 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.
If that were true, we’d all be taking trains and boats everywhere. We aren’t.
Surprisingly, at least in theory, and probably in practice with better technology, supersonic travel can be as efficient or even more efficient than subsonic flight. Supersonic travel opens up higher altitudes, higher altitudes means less air resistance.
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.
The technology of air travel may seem counter intuitive when your frame of reference is the Moore's Law.
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.
One big reason supersonic can be economic now is the increase in wealth in Asia since the 80s.
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.
I'm excited for progress in supersonic flight because fast things can be qualitatively different. I first remember hearing this idea from Linus Torvalds, talking about developing Git. He said he works differently, not just faster, when merges are instant and easy.
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.
Not a word on the environmental impact. We need to be flying less, not faster.
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.
I spent a lot of my 20s and early 30s as an environmental activist. I'm now in my mid 40s. One of the biggest things I've learned is that the vast majority of people will never make that trade. We are going to heat up the Earth. And then we are going to deal with the consequences.
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[ 5.0 ms ] story [ 72.0 ms ] threadThere is a proven middle ground, where you can pay the current price or x the price for 2x the speed.
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?
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.
That said, it might still be flying if its recertification flight hadn't happened on 9/11.
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...
So the environmental impact isn't even worth mentioning?
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.
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?”
What does that end up doing to the cost of a seat in coach?
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"?
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.
If that were true, we’d all be taking trains and boats everywhere. We aren’t.
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.
Nice (misleading) buried lede re: Boeing I suppose.
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.
1. https://news.ycombinator.com/item?id=11329286
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.
Spacex and blue origin has already demonstrated heavy payload transport, why can we just move to this than work on supersonic
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.