

Skylon: A British dream of space - ColinWright
http://www.bbc.co.uk/news/science-environment-17851603

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mkn
I've always been skeptical of these liquid-air cycles, but this scheme strikes
me as especially problematic in that an ejector ramjet would be mechanically
simpler and have the same top speed. For the curious, an ejector-ramjet (or
ram-rocket or air-augmented rocket or any of a number of other names) is just
a ramjet with a small rocket motor behind the center body of the diffuser. The
exhaust plume entrains the inlet air, boosting the combustion chamber pressure
by cooling the rocket exhaust plume. (It also acts as a fairly, err, robust
flameholder.) If you're wed to LH2 as a coolant, just bleed it in along the
walls of the rocket combustion chamber, and it will mix with the main mass
flow and combust. Et voila! The cooling system is the fuel injection system
for the ramjet mode.

Now you just spend all the compressor and heat-exchanger machinery weight that
you saved by not going with the Skylon engine by having dedicated thrusters
elsewhere on the vehicle for the pure rocket mode.

As someone somewhere else said, Skylon strikes me as a characteristically
British solution to the problem, just due to it's sheer over-reliance on
plumbing.

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jessriedel
>Every space launch for the past 60 years has involved blasting off vertically
and jettisoning separate stages once the fuel they carry is exhausted.

This isn't quite correct, right? There has been at least one LEO launch
systems which utilized a horizontal take-off. The Pedasus rocket from Orbital:

> The Pegasus rocket is a winged space launch vehicle capable of carrying
> small, unmanned payloads (443 kilograms (980 lb)) into low Earth orbit. It
> is air-launched, as part of an expendable launch system developed by Orbital
> Sciences Corporation (Orbital). The Pegasus is carried aloft below a carrier
> aircraft and launched at approximately 40,000 ft (12,000 m). It flies as a
> rocket-powered aircraft before leaving the atmosphere.

<http://en.wikipedia.org/wiki/Pegasus_(rocket)>

The author probably meant the Skylon is special because it would be the first
single-body craft to takeoff like a plane and get to LEO.

~~~
arethuza
Also two flights by the X-15 to space:

<http://en.wikipedia.org/wiki/North_American_X-15>

~~~
stcredzero
The X-15 is only suborbital, however.

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iwwr
The trick is using a conventional jet engine (as opposed to a (sc)ramjet), but
cooled with the cryogenic rocket fuel. In effect, this is using the fuel as a
heat sink, then expelling the fuel in the jet or rocket exhaust.

~~~
tocomment
No, it sounds like they're using liquid helium to cool it. But your idea
sounds like it's worth trying.

~~~
dasmoth
The helium is just a recirculating coolant.

In the test rig, it's being cooled by boil-off of LN2. In a flight
configuration, using cryogenic propellants as a heat dump seems logical.

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tocomment
How do they prevent icing when they cool the air?

~~~
russss
Well, this is their secret sauce, which they claim will make the SABRE engine
work where other scramjets have failed.

The tests they're currently running are of the pre-coolers, which have a
proprietary design to prevent icing. If it works, they will have overcome the
biggest hurdle to building a hybrid scramjet/rocket engine.

~~~
tocomment
Hmm so no one knows. What are known strategies for combatting icing? Maybe
ultrasound? Microwaves? Chemicals?

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tocomment
I'm also confused when they switch to rocket mode do they have a way to
"close" the jet engine intakes?

~~~
nicholassmith
"Beyond Mach 5.5, the air would still be unusably hot despite the cooling, so
the air inlet closes and the engine relies solely on on-board liquid oxygen
and hydrogen fuel as in a normal rocket." that's straight from the wiki page.

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gee_totes
Related, another British dream of space:
<http://en.wikipedia.org/wiki/Ministry_of_Space>

~~~
rbanffy
Don't forget <http://en.wikipedia.org/wiki/Thunderbirds_%28TV_series%29>

The 21st century used to be way cooler than it is now.

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rbanffy
I don't think the Skylon will ever be practical, but it's easy to imagine a
multi-reusable-stage launch system combining air-breathing jet engines and
wings to take you to 60,000 ft, a second one with Sabre-derived designs and
tiny wings to add a couple Mach and getting to the upper stratosphere and a
third one that can get to orbit.

The SpaceX folks should talk to these guys.

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berntb
What I never understand when reading about Skylon, is why the project try to
do single stage to orbit _directly_? A reusable first stage would in itself be
valuable and neither cost so much to develop, nor be risky by walking the edge
of weight gain etc. ssto could be version 2.

(I'm not that knowledgeable on the subject, flame me if your day has been bad,
just add information. :-) )

Edit: Symmetry, SpaceX is itself trying for reusable stages. As far as I can
tell, it should be the sweet spot?

~~~
cpleppert
Single Stage to Orbit (or any type of reusable launch system) invariably adds
complexity and weight, which in turn eats up any gains by being able to reuse
stages. It just isn't worth it to add complexity unless you go whole hog and
make the entire thing SSO.

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sek
Why are they complaining so much? If it works DARPA, SpaceX, VirginGalactic,
ESA and NASA will pay more than you can ever spend. When they didn't get the
attention of these guys so far, there is probably a mayor catch.

Edit:

What i mean is this part:

> To succeed, it needs to capture a healthy slice of the market for satellite
> launches. That's the biggest potential earner. But to do that, it must prove
> viable.

The story from the garage and share of satellite launches, that doesn't sound
like a plan. That sounds like someone who want's to be like NASA, there was
nothing in the article about reducing costs and LEO or anything business
related.

> He intervenes. "Not 'could'," he says. "It's not 'Skylon could make space
> travel easier'. It's 'Skylon will make space travel easier'."

Skylon, makes space travel easier. Now on Kickstarter.

~~~
cpleppert
Because their financial projections are bunk and are ridiculously understated.
Every piece of technology on the vehicle is custom made. Even if you accept
all their projections you still have to assume that they develop it in time
and that it works as intended. Any weight overruns will literally make the
vehicle unusable.

~~~
sek
If they have a revolutionary technology and they can really show that these
billions will provide the most competitive way of Space travel. There are a
dozen companies and well funded government agencies who have the money and
could provide most of the infrastructure they need.

Why is nobody interested? If there are big reservations, why do they start
with satellite launches? Why not start by making more powerful engines than
Rolls Royce, and sell these to all the candidates who are interested.

I have a concept for a better Operating System, i need a big chunk of OS
sales. I need Billions to have something comparable to Microsoft. Btw it's a
British operating system, the government should give me the money.

~~~
russss
They _are_ starting with engines. The rest of their ideas are simply concepts
at this stage. It's a small company.

The problem is that plenty of people have tried and failed to produce a
successful air-breathing rocket engine. Nobody wants to invest any money in
Reaction Engines until they can prove that the core concept that the company
is built on works. And proving this costs a certain amount of cash. Some of
this is being financed by the ESA, in very much the same way that NASA is
financing new commercial spaceflight efforts.

In the next year or two we're either going to see them succeed and garner lots
of investment, or fail and fade into obscurity.

