Air-breathing rocket engine set for key tests
bbc.co.uk
bbc.co.uk
Mind you - it would be fantastic to see this become a reality.
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.
No man's sky is worth a look if you like the explorer aspect as well.
Universe is vast and varied and it's come a long way since the disaster that was it it's launch.
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.
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.
Of the various designs I've seen via wikipeda, Reaction Engines PR, and on-line forums, it seems that the thermal management proposals are :-
* Bigger lighter air frame will do more thermal soak than other spaceplanes (I mean, what else is there apart from Shuttle and X15?)
* Retain some fuel to be circulated through airframe during decent, and then used for powered landing
* Less intense re-entry profile to avoid sharp heat spike, but at expense of longer thermal load
* Avoid going all the way to orbit, using a small final booster for orbital insertion
If they can harvest enough LOx/air in the final ascent, then they could also do a retro burn I suppose.
Perhaps a mix of all these, plus heat shields. SpaceX are learning how to deal with similar issues right now too.
Buran, X-37 .
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.
How does this technology compare with Ramjet technology and X51?
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.
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
My ideal combo would be superconducting maglev high-speed trains coupled with nuclear power to deliver the electricity.
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.
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.
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.
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.
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).
Just a few other numbers for reference:
Shinkansen: 0.07G
ICE (German HSR): 0.05G
S-Bahn (metro transport): 0.1G
Plane take off: 0.4G
Roller coaster: 0.5G
Another factor - half of all train passengers are facing backwards.
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.
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.
Could a hypersonic “plane” operate from ordinary airports near cities, or would it need to be operated from remote, unpopulated areas for environmental reasons?
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
I grew up near 2 airfields with rather intense traffic, with one hosting the infamous tu95, and military jets regularly engaging afterburner.
I say, the noise of a big city during day is incomparably louder than that...
This being said regular passenger planes are not that noisy compared to military and supersonic ones.
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.
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.
As where I spent childhood, it's a town near Blagoveschensk. As for the question what tu95 was doing so far away from arctic, I have no idea.
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.
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.
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.
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.
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.
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.
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.
I am not convinced that this is not military development.
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.
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.
It seems likely that an SSTO will need as much performance as possible which may only be possible with hydrogen.
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 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.
Or do they just boil of the nitrogen into the atmosphere and need to take a supply of it for the whole trip?
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.
(IIRC the trains often go closer to your real destination as well. Planes get pushed to the less influential suburbs due to noise problems)
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.
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.
https://www.nextbigfuture.com/2017/08/fully-reusable-spacex-...
It's really difficult to beat rockets for launch to orbit. Air breathing may make more sense for cruise missions.
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
Thanks for the correction, HN!
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.
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.
https://en.wikipedia.org/wiki/Environmental_aspects_of_the_e...
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, burning pretty much anything at high temperatures in our atmosphere will result in interesting nitrogen compounds.
I'm sure that the _emissions_ of the H2 engine are cleaner, though.