
Reaction Engines brings us a step closer to Mach5 commercial air travel - kareemm
http://www.thestar.com/news/the_world_daily/2014/08/uk_project_brings_us_a_step_closer_to_ultra_high_speed_air_travel___along_with_simpler_satellite_deployment.html
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idlewords
We're not going to have Mach 5 commercial air travel for the same reason we
don't have Mach 2 or 3 commercial air travel. The economics just don't work.

That reason is much more boring than the technical obstacles, which are
formidable, fun to try to solve, and kind of beside the point. In that sense,
this problem resembles a lot of software engineering.

But just to keep this comment from being too depressing, here's one technical
gripe: consider that liquid hydrogen is an extremely bulky fuel, even if you
don't include the necessary insulation. Notice how nearly the entire volume of
the satellite launcher in the diagram consists of hydrogen tank. There's not a
lot of room in there for passenger lounges and drink trolleys.

~~~
twic
> The economics just don't work.

Given that you don't know how much this will cost to operate, you can't
possibly know that, right?

At some point, i think i read a claim that an airliner based on this
technology would be able to supply Europe - Australasia trips for about the
same price as a business class ticket on a conventional airliner on that
route. Passengers currently buy a fair few of those tickets; some might choose
to do the trip in two hours instead of twenty-four in exchange for a smaller
seat and the loss of a couple of meals.

~~~
jvm
Is there really a tremendous amount of demand on the Australia / Europe
segment? If London/NYC wasn't viable for the Concorde (probably the most
popular international airline segment), I can't imagine the demand being
higher on routes to Sydney.

If the fixed costs of a flight are high, it will likely be even more expensive
than the Concorde on trans-Atlantic routes.

~~~
timthorn
Concorde reportedly made BA about £750M.

I'm not sure whether that figure takes into account the development costs -
but the reason that it was retired was due to Airbus withdrawing support.

[http://www.concordesst.com/retire/faq_r.html](http://www.concordesst.com/retire/faq_r.html)

~~~
idlewords
The CEO of Airbus said in the Financial Times that "The costs of operating
Concorde, and in particular maintenance and support, have become such that
operations are unrealistic for any operator."

The reason BA booked a profit is because of massive de facto government
subsidies for Concorde, for reasons of national prestige.

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ChuckMcM
The trick is, and it is a trick, to "instantly cool the air". Think about that
for a moment. Generally the way most 'air breathing' engines work is that they
take air, heat it (which expands it (thanks Boyle!)) and toss it backwards
which imparts a forced in the forward direction (thanks Newton!). The
difference in temperature between the inlet and exhaust temperature of a jet
engine is a component of its efficiency. (see
[http://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency](http://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency)
for some math :-)

But basically if you're suddenly cooling air it gets smaller, which creates a
lower pressure, and was used effectively in steam pumps to create the vacuum
needed to lift water out of mines.

So the Reaction Engines concept takes really hot air that is compressed
because it is being pushed out of the way by the air frame, then super cools
it which causes it to become much smaller, and then dumps that into the
engine. Which then heats it up again and pushed out.

If I understand the theory correctly, it takes heat from the air, removes it
and puts it into liquid hydrogen (which then becomes vaporous(sp?) hydrogen)
and then burns that hydrogen with residual oxygen to put the heat back into
the air plus what ever is extra from the hydrogen. What bugs me about it is
that it seems to double count the energy in the air rather than single count
it. But I'm interested in seeing one of their machines in action. If someone
knows whether or not there is a violation of thermodynamics in there I'd like
to understand that.

That said a mach 5 vehicle with a range of 12,000 miles and a payload capacity
of 15 tons has much more interesting uses than carrying passengers I think.
Would make a heck of a cruise missile.

~~~
trhway
>That said a mach 5 vehicle with a range of 12,000 miles and a payload
capacity of 15 tons has much more interesting uses than carrying passengers I
think. Would make a heck of a cruise missile.

yes and no. No - early detected and easily destroyed even by previous
generation of anti-missile systems. This is basically why Valkyrie and the
likes were scrambled 50 years ago. Yes - quick deployment against countries
still not having any meaningful anti-missile defense :)

Also, quick jumps above 60mi (space international border) would probably allow
to legally fly modern day U-2 style missions over some relatively narrow
territories like over Crimea, Cuba, North Korea, etc...

~~~
XorNot
The working hypothesis at the moment is that that type of suborbital
hypersonic aircraft is what's being built by the US at Area 51 these days.
Certainly the focus of public research funding has had that theme to it.

~~~
trhway
well, judging by nobody hearing the sonic booms - somebody living in CA would
definitely hear it when it would be going into Pacific, i think X-15 and
Branson are the closest takes on it (both being almost the same actually, and
military can realistically use such approach today, though no country has
reported such flyovers and considering that it can be easily spotted if
used...).

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parley
In a previous post (a little over a year ago) about the same engine I posted a
link to a video with a Q&A with Elon Musk where he was a bit pessimistic about
the idea.

I'm not a rocket scientist so I wouldn't know the first thing about it, but if
anyone is interested in his (then) opinion it's after 48m55s in the video
here:
[http://www.oxfordmartin.ox.ac.uk/videos/view/211](http://www.oxfordmartin.ox.ac.uk/videos/view/211)

~~~
XorNot
Elon Musk isn't the expert in this area. Practically no one except Reaction
Engine employees and some guys at Area 51 are - in the entire world. It's
certainly not an easy thing to do, but since they actually do seem to have the
heat exchanger figured out then that's kind of a big deal.

Burying the lead is the whole commercial air travel angle though. What they're
building is a fully reusable, cheap to operate SSTO to low earth orbit.

~~~
bjelkeman-again
ESA did a review of Skylon and the Sabre engine and said "...the SKYLON
vehicle can be realised given today's current technology and successful engine
development."

[http://www.reactionengines.co.uk/space_skylon.html](http://www.reactionengines.co.uk/space_skylon.html)

Of course, there needs to be a successful engine development project. Which
needs another billion or two to complete according to the CEO/MD of Reaction
Engine. (He was a bit more specific than that when I heard him say it, but it
is in the ballpark.)

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trhway
the thermodynamic economics of ram/scram jets at the Mach5+ speeds is almost
killed compare to the rocket engines by the fact that oxygen is only 20% of
the incoming air, while the whole incoming air needs to be processed through
the engine, ie. compressed/(may be cooled interstage)/heated/expelled. Various
unavoidable losses on this 80% (nitrogen) of the incoming air eat deeply into
end-result efficiency of such engine when compared to a rocket engine.

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ufmace
Sounds a little odd. I'm not really an expert on this area or anything, but it
sounds plausible that if they are able to cool the incoming air stream to that
temperature, then they might be able to make the speeds they're claiming. But
I have to wonder, not only how they made a heat exchanger capable of cooling
the incoming air that fast, but what are they doing with those megawatts of
heat that they're taking out of the air? They claimed air temperatures coming
out of the heat exchanger of -150, so where are they getting a cooling fluid
colder than that to do exchange with?

~~~
idlewords
The incredibly huge tank of liquid hydrogen not pictured in the diagram. The
same one that makes the idea completely unfeasible for commercial transport.

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findjashua
I'm assuming this can't be used for flying over land due to sonic boom?

~~~
masklinn
Depends which land and — most likely — depends who builds it.

It's not like the US forbid overland supersonic flight for their military
planes (and overland commercial supersonic flight was only banned as the US's
sole SST program was cancelled)

~~~
hollerith
During 54 years of living in 5 different metropolitan areas of the U.S., I've
never heard a sonic boom. (I know what one sounds like because they were
frequent during a vacation I took in West Germany a long time ago.)

The Blue Angels, for example, are not authorized to exceed the speed of sound:
[http://www.blueangels.navy.mil/show/faq.aspx](http://www.blueangels.navy.mil/show/faq.aspx)

~~~
rsync
I lived near colorado springs in the early 80s, as a child, and I can remember
on two occasions being (figuratively) knocked out of bed by a sonic boom.

Presumably from the Air Force Academy. Only happened those two times the
entire time we lived there - presumably someone got in trouble for it...

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sp332
So they can cool the engine, but what about the heat on the rest of the plane?

~~~
NamTaf
That's not the problem. The problem is that hot inlet air means that once you
burn your fuel, the air post combustion stage is then too hot and melts
things.

~~~
idlewords
It's a huge problem, unless you don't mind a flying oven. In the SR-71, the
crew had to wear special cooling suits (presumably these will be available in
first class).

~~~
NamTaf
What I mean is that from a material standpoint, the engine turbine temperature
tends to be the design limiting factor.

Yes, there's going to be hot spots on leading edges due to stagnation for
example, but you're not burning fuel there to intentionally jack the
temperature up.

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lubesGordi
the video is 2 years old

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soperj
I've read about this before, and I do think it sounds pretty neat, but a small
part of me hopes it doesn't work for putting satellites into space, only
because the technology doesn't help us land on other planets.

~~~
acchow
I disagree. Familiarity with microgravity and the vacuum of space in orbit
will make developments in interstellar travel that much cheaper.

~~~
idlewords
I think we're pretty familiar with vacuum at this point. The obstacle to
practical interstellar travel is 99.99999% propulsion, which you don't learn a
lot about by endlessly falling in a circle.

~~~
XorNot
And the obstacle to propulsion is the inability to lift large payloads cheaply
enough into orbit to start with.

The problem is we can't build big things in LEO. At the moment its that our
entire LEO-access infrastructure is woefully underdeveloped.

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TeMPOraL
Nitpick about the title[0], but it's a kind of thing that really irks me. It's
"Reaction Engines", not "Reaction engines". It's a _proper name_ of a private
limited company, not a class of engines.

[0] - at the time of writing this, the title was: "Reaction engines bring us a
step closer to Mach5 commercial air travel".

~~~
alexvr
Based on the grammar following "Reaction engines," it's clear that the OP
simply thought the new engine was actually called a "reaction engine"

(I'm sure the author would not write "Google bring us closer to autonomous
cars")

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MaysonL
The Star is a British paper: UK usage would be Reaction Engines bring, and yes
the author _would_ write "Google bring...".

