I was fairly young at the time but still remember _Tomorrow's World_ (A BBC TV show about science and inventions) talking about HOTOL. To ~6 year old me, raised on watching Thunderbirds, Star Trek and NASA launches, it felt great that we'd be getting our very own Shuttle.
Much much older me loves messing around with scramjets and air-breathing rockets in Kerbal Space Program. Or spending real-world months exploring the Perseus Arm of the Milky Way in Elite: Dangerous. I guess our imagination always outstripped our ability, but to be honest I don't mind so much nowadays. Mostly because I'm partially disabled and would never get on any kind of space or Mars missions to start with.
VTVL (vertical takeoff, vertical landing) rockets have been talked about since sci-fi in the 30s and seriously since the 50s. We only just started getting real ones (SpaceX, Blue Origin), though in the 90s there was a prototype called the DC-X that proved the concept at a smaller scale. You can find DC-X videos on YouTube.
The fact that something was talked about long ago and we don't have it yet doesn't necessarily mean there's something wrong with the idea. Sometimes all it takes is for someone to just do the engineering, which with high-capital stuff means it also takes someone being willing to pay for it.
Of course the other case is things like net-positive fusion where people have been doing the engineering but it's f'ing hard. Still given the progress that has been made on fusion I get the sense we could do it if we spent more and put more parallel effort into it.
I am the same and can remember getting excited about it back in the day. I find it difficult to regain that excitement. This is especially true given the things that companies like SpaceX have achieved, let alone what they are working on.
The air breathing operates upto mach 5.14 and 28km (which is higher and faster than an SR71).
That would be about 5500km/h. The first stage of a falcoln 9 on the recent flight was 6,600kph and 91km high, so not a direct comparison but fairly close.
Re-entry heat shields is still going to be a problem if it goes to orbital velocity of 27kkph for something that's reusable.
How exciting! Never expected this to come out of the vapourware stage, the technology sounded just too improbable. Sure would be nice to have an ambitious EU counterpart to SpaceX.
Maybe I can get away with the observation that this kind of prestigious engineering project has traditionally been a magnet for proud mercantilists.
The Science Museum's book about Concorde contains a breathtaking interview with an engineer who is very keen that technological innovations are not shared with the industries of other countries. Very myopic.
Its interesting to know that they are finally testing. I remember reading about Reaction Engines back in 2012 (I was in college) and them working in this technology. Back then it was in primordial stages.
How does this technology compare with Ramjet technology and X51?
Scramjets minimise compression losses by minimising compression...
Sabre minimisies compression losses by instantly cooling incoming hypersonic air stream with their tricky heat exchanger, thus not doing compression. The turbocompressor after the precooler is pretty much a pump.
Interesting, thanks? You seem knowledgeble on the subject, what's your take on the commercial and technical viability of this tech in general and REL's abilities to execute more specifically in the case the tech is viable.
My common sense says that tech is not viable, but reality shows otherwise. Thus, I can't tell much about it from my common sense. The company must be staffed by much more competent engineers in their domain than I am.
The most tricky parts in my view are the pre-cooler just for the giant mass flow and temperature difference, and the helium/lh2 heat exchanger, but those two seem to been done. O_O
I see what you're saying but innovation in high-speed mass transport is going to take a breakthrough in tech: could be sabre, could be hyperloop, could be superconducting maglev. Despite what your spidey-sense is telling you, maybe this is one of the breakthroughs we need. Having said that I think we should be aiming for low environmental footprint with all our tech from now on given what we know about the damage we're doing. I'd like to see these breakthrough techs compared in terms of environmental costs.
My ideal combo would be superconducting maglev high-speed trains coupled with nuclear power to deliver the electricity.
For mass transit high speed only makes sense for longer distances. Most mass transit is relatively short haul where the acceleration/deceleration times (that still provides a comfortable ride) prevent you from saving any time.
Over the speed of sound is great if you want to fly half way around the world. But from Paris to London it doesn't really save you much. Unless it becomes cheaper than regular air travel.
> For mass transit high speed only makes sense for longer distances. Most mass transit is relatively short haul where the acceleration/deceleration times (that still provides a comfortable ride) prevent you from saving any time.
Probably I just should have said superconducting maglev trains. I guess you're right that they only need to be properly high speed over longer distances. Superconducting maglev would be a win for acceleration/deceleration as well so would benefit short haul.
Realistically speaking, inexpensive superconductors would be a total game changer for many fields, not just mass transport.
> Over the speed of sound is great if you want to fly half way around the world. But from Paris to London it doesn't really save you much. Unless it becomes cheaper than regular air travel.
I kind of feel that in general it'd be better to replace planes with trains, than to replace planes with better or faster planes. Better security-wise. Better for the environment in the long run I believe. I'm totally open to correction though.
> Superconducting maglev would be a win for acceleration/deceleration as well
This limitation isn't at all technological. You just can't accelerate or decelerate much faster than today's high speed trains without causing discomfort to your passengers. And the radius of any turn increases with speed. Otherwise first you just produce noticeable discomfort while turning, and beyond that you risk derailment (no matter the rail type). So you're basically stuck with having really long and very straight stretches of rail where you have to gently accelerate and decelerate. On any short trip this would kill any economy of high top speed.
> I kind of feel that in general it'd be better to replace planes with trains
The advantage of flight is that you are free to take a more or less straight path between the 2 points without caring about what's below. But with any kind of land transportation you need to deal with rivers, mountains, lakes and seas (not to mention oceans), cities and other man made structures, etc. Without a breakthrough in engineering I don't see how you can go from London to Los Angeles in a reasonable time.
> This limitation isn't at all technological. You just can't accelerate or decelerate much faster than today's high speed trains without causing discomfort to your passengers.
Will electric cars change people's comfort with longitudinal acceleration? Imagine people's family SUV does 0-60 at 5 m/s^2 (Tesla Model Y), and sedan around 10 m/s^2 (Model 3 and S). Then subway's ~1 m/s^2, shinkansen's 1.2, or TGV's 0.5, may seem very last century. A generic Honda Civic looks about 3.
We can do it but it won't be comfortable. It would be "roller coaster fun" (similar acceleration). You have 500 people on a train (half of them facing backwards) and want to give them a comfortable ride. Including keeping the coffee in their cups or their stomachs :). Again, it's not a technological challenge, it's a biological one. The human body doesn't evolve faster because we have capable cars.
At 5m/s^2 we're talking ~0.5G, more than what you feel in a plane taking off (normally ~0.4G) and one order of magnitude higher than most high-speed trains accelerating (~0.03-0.05G). This is not a normal or comfortable regime. And at 0.2G lateral acceleration (in curves) you have a good chance of seeing your lunch again. This means at 600Km/h you need 15-20Km turn radius. Add to that the air turbulence at close to and over 500Km/h at sea level which causes a rumble that's nausea inducing for most people (riding in low pressure tubes may help here).
People don't expect to be able to get work done in a passenger car. Train passengers (especially the lucrative business sector) expect their laptops to stay on the table.
Another factor - half of all train passengers are facing backwards.
If you are interested, Kerbal Space Program has mods for ramjets/scramjets, and the air-breathing rockets are part of the base game now. You can build your own Waverider and mess around with all sorts of fun explosions and crashes!
> I remember reading about Reaction Engines back in 2012
I'm not sure but I think I first watched a CGI rendering of Skylon in the early 2000s (back when I was still a student). I've tried to find the video on YouTube to find out its publication date but it appeared more difficult than I expected.
Anyone can find the original video I'm talking about? It's definitely not on the official RE Youtube channel anymore.
I use air breathing engines for small single stage orbital vehicles in KSP. They are much more fun to fly, albeit you have to stay in atmosphere for a longer time due to very low degree of ascent to gain speed :)
If I have to go further, I make it two stage, with the last stage traditional booster stage. Anything bigger than that tends to fail though.
How does this compare to Concorde, and contemporary aircraft, with regards to emissions and noise levels?
Could a hypersonic “plane” operate from ordinary airports near cities, or would it need to be operated from remote, unpopulated areas for environmental reasons?
Energy use is another factor. The EU just nixed rules which could have allowed new generations of supersonic air travel due mostly to this concern.
This seems to be inherent to the physics: air resistance rises with the cube of speed. You could make up for it by flying higher, but then you're expending more energy to get up there.
An engine consuming hydrogen may open a door for renewable production. But we're not at the limit in what the grids can absorb, and may never get there with how battery storage and smart consumer-side tech is advancing.
The same way, modern noise level limits on airplanes were pretty much imposed to prevent soviet made aircraft from flooding the market after USSR collapse
Not just sonic booms though. Those engines were spectacularly loud going over populated areas. It used to come over me in the western edges of London on a regular basis, and the whole earth shook when it did.
I remember spending a lot of time at Heathrow in the BA departure lounge waiting for flights to Edinburgh - normally you couldn't hear very much (if anything) from outside. Then the whole place would shake and you'd hear an impressive roar from outside and you'd know a Concorde had taken off.
Concorde was only louder than the rest on takeoff and initial climb out - because the reheat was on. Reheat is stupidly loud. Reheat was needed as it was optimised for super cruise (sustained supersonic) - something even fighters aren't, which made it very inefficient at takeoff speeds.
On approach and cruise it wasn't that much different from other jets of the era.
Modern engines could be far quieter and not need reheat for takeoff.
Several years ago a Eurofighter was scrambed to intercept what they thought was a hijacked plane; I didn't realise this at the time but the sonic boom shook my flat and the windows, not that I minded in that case, but I wouldn't want to make a habit of it.
Which set me to thinking, how much energy must be sapped away by the sonic bow shock, to make such a loud sound across such a wide area must be be exteremly inefficient.
Also I've been interested in Max-Q, the fact that a rocket has to limit its speed to reduce aerodynamic stresses on its structure, not something I've thought much about before.
A "regular jet" has turbofan engines where the center section of the jet, the part that actually compresses air and burns fuel, is used to spin a big fan which supplies a good chunk of the thrust. The fan is relatively quiet compared to the actual fuel burning section of engine because it is exhausting gas at much lower pressure, think popping a balloon vs popping a tire. For a variety of reasons that you can google high bypass turbofan engines are not used on supersonic aircraft. This means all that thrust is coming from the actual engine itself.
Per unit of thrust an aircraft that doesn't use turbofans is just going to be louder.
So Concorde is just going to be louder than a "regular jet" but nothing special compared to any other jet making the same amount of thrust from similar engines. For acoustic purposes you can think of the Concorde as basically being two heavy fighter aircraft.
Edit: Running the numbers based on Wikipedia specs for thrust with afterburners the Concorde is making about the same amount of thrust as four F18s. So throttle on the firewall Concorde should make about as much noise as the Blue Angels. That said, lighting the burners over a populated area would be a great way to wind up looking for a new job.
Yes, a lot louder. I lived well outside London, and I'd say Concorde flying over Reading (by which point it was _high_) was louder than the memorable time a C-5 decided to take off from Greenham Common right over my house.
I used to live near central London (NW6) and would be driven mad by Heathrow aircraft, because many late-night Asia-bound departures would overfly my house. It often seemed roof-shakingly loud, and was incredibly annoying when I was trying to get to sleep. (Although there was supposed to be an 11PM curfew, they would often depart late, sometimes after midnight.)
Right now I live in far west London (UB3), only a mile or so from Heathrow's northern runway. On the 6th floor. It's blissfully quiet. I can see the aircraft but not hear them. Turns out that aircraft coming in to land, even relatively close at low altitudes, are much less noisy than departing aircraft directly overhead.
I slowly learned to hate the Blue Angels because the city of Seattle let them buzz downtown during their practice sessions every year, with after burners. If the burners went on anywhere over downtown you had to pause your conversation. Indoors.
Every fucking year. Including the years after 9/11, when the sounds of a military jet in a densely populated area took on more sinister undertones. Oh shit, are we fucked? No, it,'s just SeaFair.
First year: Oh cool, Blue Angels! After five years? Fuck you, Blue Angels.
Do you mind me asking which city that is? I'm curious because after living in multiple big cities I found that sometimes one city was much louder than living next to the huge airport of another city.
This being said regular passenger planes are not that noisy compared to military and supersonic ones.
I live in London and in my experience, the vast majority of problematic urban noise comes from two sources: overflying aircraft (mostly from to LHR and LCY airports), and modified or poorly maintained motorcycles.
Aircraft are improving with each generation but are still extremely noisy when they're directly overflying you, even many miles from the airport.
While there are certainly other sources of urban noise, like heavy goods vehicles and construction, these are strictly regulated and enforced with regards to operating times, etc in the UK - while noise from aircraft and private vehicles is not.
Sirens (fire, ambulance, police) can also be very loud, but I'll give them a pass because they are actually serving a useful purpose and saving lives. In the future when vehicles are quieter due to electrification, I think we'll be able to reduce the volume of emergency sirens too.
Those weird scallops on the back of all recent vintage Boeing planes are for noise reduction.
I couldn't find a quote or number on how many decibels it reduces the engines, except a note that:
| The acoustic liners and chevrons are such effective noise suppressors that several hundred pounds of sound insulation may be eliminated from the fuselage.
I'm just guessing but Shenzhen might be an outlier when it comes to "regular" noise pollution in a city. Most cities would be comparatively quiet and hypersonic flights over them would be quite disturbing.
This would still use hydrogen, and liquid oxygen which are more difficult to handle than jet fuel. Having such fuels in close proximity to people could be pretty risky.
Also, it is not known what the take off or landing speed would be like. A hypersonic vehicle needs wings that are very swept back and would not generate a lot of lift at low altitude. That means higher speeds, longer runways, and more risk.
It is worth noting that H2 is not fundamental to the design. Just as the American space industry is transitioning from H2 to LCH4, so too could these 'rockets' use methane. Though methane has half the energy density per kg than hydrogen, it has seven times the energy density per unit of volume. That is a lot of tank structure than can be saved, not to mention a much nicer ballistic coefficient.
I'm really hoping that now that we have two methane-powered rocket engines coming online in the near term (Raptor and BE4), that the designers of Sabre and other hypersonic technologies might look at methane a bit more seriously.
This engine is meant for Skylon spaceplane, an unmanned cargo vehicle. As for noise, there are no reasons to have it overflight any populated areas. I presume there would be less noise abatement technologies employed due to need for efficiency.
As for emissions, close to none. The engines are supposed to burn hydrogen, and other emissions (brake pads wear, in-orbit maneuvering via cold thrusters) are minuscule.
This engine is meant to bring stuff (and people) to low earth orbit. Don't think of it as a plane, but as a space shuttle which will be fully reusable with no additional boosters.
It flies at up to mach 5 and then switches to rocket mode, thus using it's own oxydizer instead of using the one in the atmosphere.
The Concorde was also limited by where it could fly. There's a limited set of routes you can take before it becomes even less economical by flying a path over water or unpopulated areas. You'd never be able to fly London to New Delhi in super/hypersonic mode I guess.
The Rolls engines designed for HOTOL were meant to do the same, by a different method. They were going to use the hydrogen fuel to operate the intake heat exchangers. The engine then burnt hot hydrogen. Any excess was used as reheat injected into the exhaust.
There was a movie showing their heat exchanger test going around. It is a gas to gas (helium.) And you can pump helium at very high flow rates. Speed of sound in helium is 1000m/s after all.
This is very cool. But, there are two ways to make your trips shorter:
1 - make them feel shorter by providing some luxury, comfort, ability to sleep watching movies, or remaining predictive, etc.
2 - go faster and reduce the travel time.
There is a cost/benefits points where 1 vs 2 will not make economic sense, even for very wealthy.
This is why I think, this kind of technology will mostly work and see demands in military applications and not so much for jet-setting around the world.
Even with current airplanes, for most trips the hassle is all the stuff that involves getting on the plane in the first place. Once you are in your seat, you can either relax or by relatively productive with your laptop+in-flight wifi.
On a 20h+ flight to Australia, I guarantee you, you will want it any possible minute shorter.
Not even mentioning how shorter travel time could help with Jet-Lag.
I can see many reasons why we may want to push both in the 1 and 2 categories!
Right, I agree. But I suspect these types of flights make up a fraction of the total number of business related flights in a year. I can't prove that though, would be interesting to see some figures on that.
Once you are in your seat, you can either relax or by relatively productive with your laptop+in-flight wifi.
I think that's only true if you fly first-class (domestic) or business class (or maybe premium economy) international.
In standard Economy I can't open my 15" laptop screen all the way, and when I try to use my keyboard, my elbows poke the person in the seat(s) next to me. So being productive while flying is not an option.
The economics don't support giving people adequate space, so reducing the time in flight is a big win for everyone.
Upgrading to a 'sane' amount of legroom cost me 40 bucks on my last flight as I recall. Even if time in the seat is 100% wasted time, all the ancillary stuff like getting to and from the airport, security, rental car, bag check, etc, etc is a significant % of the overall time expenditure for all but the longest flights.
It varies widely among airlines, the last time I booked United for SFO->SEA (a 2 hour flight), they wanted $89 for "economy plus" and ~4 inches more legroom. And even with the extra legroom, the seats are still quite narrow and I have a hard time using a 15" laptop and still keeping my elbows within my armrests.
I think I paid $29 for the upgrade on Alaska Airlines (though you need to do your research, since depending on the plane (Alaska, former virgin, Horizon), you may not get more legroom, just a seat closer to the front and maybe a free cocktail.
You could buy two seats, or pay extra for the ones with more legroom. I think the GP's point, say, is that you could do both (two seats with extra legroom) at ~3x the cost, so if you're trying to make flights faster you need to compete with that. Indeed, the fact that airplanes are configured the ways they are suggest most flyers aren't willing to pay much at _all_ for more comfort...so it would be surprising if they'd pay a lot more to go faster.
I'd imagine the cockpit would need to be fully shielded? Just as a fun exercise, let's calculate the kinetic energy of a 3kg goose impacting the airplane at 5000 kmh:
The formula is (m*v^2)/2.
Plugging in the figures, we get 2.9 MJ, or the equivalent of a little more than half a kg of TNT. Not bad :D
It doesn't reach 5000kmh until 26km altitude[0], but the highest geese have been reported is 9km altitude[1], so I would assume it would only be in danger of encountering geese at speeds lower than 5000kmh. (Still likely to be at pretty fast speeds though.)
IMHO it will be more challenging than just building an orbital class rocket. You have most of the challenges of space flight in terms of exotic fuels etc. But you spend the entire flight in a hypersonic airflow, where any problem could escalate instantly. At least in orbit you have time to fix things.
And the vehicle needs to work at completely different altitudes and velocities. This could be very challenging in terms of structures, landing gear, braking etc. Particularly if the mass of the vehicle is constrained. Many component will need to be lighter and have orders of magntitude better performance than a traditional airliner.
As a hydrogen engine it is also carbon neutral. That makes it more environment friendly than both the existing jet engines and Musk's methane rocket hopper.
Yeah though hydrogen is produced by burning fossil fuels currently. I hope the tech to get hydrogen from the air and water using solar keeps improving and getting cheaper to the point that it becomes the main source of hydrogen. As hydrogen used as a fuel source and as a way to store renewable energy has a huge potential to bring down the world's carbon production.
I'm skeptical about hydrogen's use as a form of energy storage but a carbon neutral source of hydrogen for chemical processes, especially the generation of fertilizer, would be a huge deal.
“Doesn’t emit CO2 when in operation” and “carbon neutral” are two completely different things.
If Musk produces his methane using electricity from the solar cells he sells, and this thing flies on hydrogen made by burning oil to drive a generator that uses hydrolysis to split water into hydrogen and oxygen, Musk’s rocket hopper can well be closer to carbon neutral.
Also, “environment friendly“ is yet something different. Using bare steel and reusing rockets, as Musk does, will help there, but this design also seems to be reusable.
> Also, “environment friendly“ is yet something different. Using bare steel and reusing rockets, as Musk does, will help there, but this design also seems to be reusable.
...also, burning pretty much anything at high temperatures in our atmosphere will result in interesting nitrogen compounds.
That comment has very little substance. Where do you get the hydrogen? Where do you get the jet fuel? The answer determines if it's environment friendly.
Yes. So-called `green tech' and its boosters have greenwashed a bunch of tech which is far from actually green and clean when you look at the details. I'm unsure whether these people are ignorant or mendacious. Charitably I'm going with the first option with a touch of the ol' ideological blinkers thrown in for good measure.
Examples:
(a – transport) electric vehicles, hydrogen-powered vehicles – In the first case, how are batteries made? where do the elements come from, what are the environmental costs? what are the human costs? what are the industrial processes? In the second case, to echo your question, great but where does the the hydrogen come from? And what about disposal and recycling?
(b – energy production) wind turbines, solar pv panels – Same set of questions: how are they made? What are the social and environmental costs? What's their lifetime? How are they disposed of or recycled?
This is a shame because actually greener tech (like nuclear in the case of energy production, and cycling and mass public transport in the case of transport) is overlooked or sidelined to the detriment of the whole planet. Unsurprisingly this childish ignorance will end up hurting us all. This stuff needs to be taught in schools.
You understand that you can google either of those and get thorough, comprehensive breakdowns of environmental costs? Because that's exactly the kind of questions that being asked by people like you for last couple decades. Not that they ever read the answers.
Reducing carbon emissions is a good thing but the emissions from a typical launch are on the same order of magnitude as flying a jumbo jet across the Pacific and rocket flights are much less frequent than that. The biggest environmental concern is the damage to the ozone layer that solid boosters cause.
Mind you - it would be fantastic to see this become a reality.