
Air-breathing rocket engine set for key tests - sambeau
https://www.bbc.co.uk/news/science-environment-47585433
======
arethuza
I'm 53 - I can remember news stories about HOTOL when I was in high school!

Mind you - it would be fantastic to see this become a reality.

~~~
bloopernova
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.

~~~
noir_lord
Bumbling around out in the fringes is one of the best things about ED I find.

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.

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isostatic
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.

~~~
delibes
The space plane ideas for using a Sabre engine are fairly early stage designs,
since the whole engine isn't even a working prototype yet.

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.

~~~
coolspot
> what else is there apart from Shuttle and X15?

Buran, X-37 .

~~~
avmich
And soon hopefully Dream Chaser.

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MrBuddyCasino
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.

~~~
sveme
EU for another 11 days, unfortunately. But this is not the place for
Brexshitting, so I'm just celebrating this regardless of any politics.

~~~
theoh
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.

------
godelmachine
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?

[https://en.m.wikipedia.org/wiki/Ramjet](https://en.m.wikipedia.org/wiki/Ramjet)

[https://en.m.wikipedia.org/wiki/Boeing_X-51_Waverider](https://en.m.wikipedia.org/wiki/Boeing_X-51_Waverider)

~~~
baybal2
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.

~~~
igravious
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.

~~~
baybal2
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

~~~
igravious
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.

~~~
close04
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.

~~~
igravious
> 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.

~~~
close04
> 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.

~~~
mncharity
> 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.

~~~
close04
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).

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

------
z3phyr
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.

------
Reason077
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?

~~~
dexen
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.

~~~
dotancohen
What type of cargo does an unmanned plane carry that needs to get to the
destination at Mach 5?

I am not convinced that this is not military development.

~~~
pastullo
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.

------
EngineerBetter
Wow. 1,500C to -150C in 1/100th of a second sounds pretty remarkable. Any idea
how that's achieved?

~~~
NeedMoreTea
A helium cooling loop, cooled by a nitrogen boiler. More info and pictures:
[https://www.bbc.co.uk/news/science-
environment-20510112](https://www.bbc.co.uk/news/science-environment-20510112)

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.

~~~
scotty79
What do they ultimately do with the heat?

Or do they just boil of the nitrogen into the atmosphere and need to take a
supply of it for the whole trip?

~~~
baybal2
They will use fuel instead of LN2 in the real thing.

~~~
scotty79
From what I heard liquid hydrogen is quite nasty. It will definitely require
different materials than ln2

------
salimmadjd
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.

~~~
TrevorJ
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.

~~~
Johnny555
_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.

~~~
TrevorJ
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.

~~~
Johnny555
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.

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pfdietz
"Fully reusable Spacex Rockets would be lower cost than Skylon spaceplanes"

[https://www.nextbigfuture.com/2017/08/fully-reusable-
spacex-...](https://www.nextbigfuture.com/2017/08/fully-reusable-spacex-
rockets-would-be-lower-cost-than-skylon-spaceplanes.html)

It's really difficult to beat rockets for launch to orbit. Air breathing may
make more sense for cruise missions.

------
jaimex2
So its a two in one engine? neat idea, hoping it goes well. This sounds a bit
nicer than blasting at high gs for quick travel around the planet.

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bibyte
I wonder if this technology will ever be viable for commercial flights in the
future. What the safety procedures would look like at that speed.

~~~
short_sells_poo
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

~~~
Hendrikto
Geese don’t fly at the height where this speed is reached.

~~~
ethbro
My 90s childhood education based on pirated floppies was apparently deficient
in the flight habits of geese, then: [https://www.myabandonware.com/game/star-
goose-ix](https://www.myabandonware.com/game/star-goose-ix)

Thanks for the correction, HN!

------
russfink
How much operational weight (fuel, power source) is there compared to other
technologies? What about range?

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syntaxing
Is this equivalent to a SC/RAM jet engine?

~~~
baybal2
No, it is very different

------
varjag
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.

~~~
jacobush
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.

~~~
igravious
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.

~~~
varjag
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.

[https://en.wikipedia.org/wiki/Environmental_aspects_of_the_e...](https://en.wikipedia.org/wiki/Environmental_aspects_of_the_electric_car#Environmental_impact_of_manufacturing)

------
growlist
I just hope they've got the IP well locked down. Bound to be lots of envious
eyes on this tech!

------
kristianp
This might be competing with SpaceX BFR taking passengers point to point. I
would bet on the BFR being more likely, proven technology vs new tech.

