Skylon spaceplane developers reveal the antifreeze method for the sabre hypersonic engine
July 11, 2015
http://nextbigfuture.com/
Reaction Engines of the UK is developing the hypersonic Synergetic Air-Breathing Rocket Engine (Sabre).
It is designed to power a vehicle from a standing start to Mach 5.5 in
air-breathing mode, and from the edge of the atmosphere to low Earth
orbit in pure rocket mode. A fundamental enabler of the concept is a
complex heat-exchanger system made up of miles of fine tubing that
allows oxygen to be taken straight from the atmosphere for use as fuel.
The system chills incoming air from more than 1,000C to minus 150C in
less than 1/100th of a second before passing the pre-cooled air through a
turbo-compressor and into the rocket combustion chamber, where it is
burned with sub-cooled liquid hydrogen. But until now the means by which
the system does this without clogging up the pre-cooler with ice has
remained a closely guarded company secret.
Reaction Engines uses methanol as an antifreeze. The methanol is used
with the objective of minimizing the amount that is needed.
They use chemical process industry tricks.
* inject the methanol at one of the coldest points
* get the mix of water and methanol to flow forward in the matrix – against the direction of the airflow
* use multiple injection and extraction points in the matrix
* Eventually you end up with a situation where you have extracted all
the water vapor as liquid from the airflow and that leaves you
essentially with dry air below 215 Kelvin. The partial pressure of the
water vapor at this point is so low that you can allow it to pass
through the heat exchanger and it does not freeze
Skylon Spaceplane
3D Printed injector
Precooler
Sabre engine
Engine test rig
Rocket nozzle
Reaction Engines decided to go public with the frost control technology
because of pending patent applications. “The trigger for patenting was
the awareness that to execute this program we are going to have to
involve other companies,” says Mark Thomas, former chief engineer for
technology and future programs at Rolls-Royce, who recently took the
reins as managing director of Reaction Engines. “You can’t keep trade
secrets very long in that situation, so it is better to be protected
formally and legally on the clever stuff.” Thomas adds that Reaction is
close to “having those approved.”
The company is developing the Sabre engine principally for the Skylon
single-stage-to-orbit spaceplane. But the propulsion system and its
pre-cooler technology are attracting wider interest for potential
aircraft and two-stage launch vehicle applications.
The SABRE engine requires a novel design of the rocket engine's thrust
chamber and nozzle to allow operation in both air-breathing and rocket
modes, as well as a smooth transition between the two. The Advanced
Nozzle project is demonstrating the feasibility of this concept and
represents a significant technology development effort towards the SABRE
demonstrator engine.
The test engine, which has been successfully fired 15 times during its
initial commissioning phase in spring 2015, incorporates several new
technologies including a 3D printed, actively cooled propellant injector
system. Aerodynamic data collected from the firings is being used to
validate in-house computational modelling and advance the nozzle design.
The test campaign is being operated by Airborne Engineering Ltd in
Westcott, Buckinghamshire. Operations are planned to continue throughout
2015, including long duration burns and tests investigating the
transition between air- breathing and rocket operation planned for later
in the year.
Dr Helen Webber, Reaction Engines' Project Lead for the Advanced Nozzle
Programme, commented:. "This experimental engine is an important step
into a new era of propulsion and space access We are using it to test
the aerodynamics and performance of the advanced nozzles that the SABRE
engine will use, in addition to new manufacturing technologies such as
our 3D-printed injection system
Reaction Engines' ultra-lightweight air heat exchangers cool hot air
from 1,000 ° C to minus 150 ° C in 1/100th second. With proprietary
frost control technology preventing the formation of ice at sub-zero
temperatures, the SABRE engine's pre-cooler is able transfer the same
amount of heat generated by electricity power stations (450MW) using
equipment that It weighs less than a standard car (less than 1.5 tonne).
Combined with unique thermodynamic cycles, Reaction Engines' technology
enables a new class of aerospace engine called the Synergetic
Air-Breathing Rocket Engine ('SABRE'). This breakthrough in aerospace
propulsion can power aircraft from a runway start up to Mach 5.5 in the
atmosphere (more than twice the speed of a conventional jet engine) and
then subtly transition to a pure rocket mode which allows the engine to
operate outside of the Earth's atmosphere up to orbital velocity (Mach
25, 17,000mph, 7.5km / sec). The viability of the SABRE engine has been
independently validated by the European Space Agency during a review
which was undertaken at the request of the UK Space Agency.
Reaction Engines Ltd has an ongoing privately funded SABRE engine
technology development programme, and in 2013 the UK Government
announced a £ 60m commitment towards the development to aid preparations
for the design, manufacture and testing of the first SABRE demonstrator
engines.
REL's technologies have the potential for wider application across large
industrial markets to improve efficiency and create new capabilities,
with applications in power generation, conventional gas turbines and
desalination.
Skylon plans and projected costs
For Skylon, if no growth occurred and all operators flew equal numbers
of the current approximately 100 satellites per year using 30 in-service
spaceplanes from 3 spaceports, the true launch cost would be about $40
million per flight [$1200/lb to LEO].
They expect mission costs to fall to about $10 million per launch for
high product value cargo (e.g. communications satellites) $2-5 million
for low product value cargo (e.g. science satellites) and for costs per
passenger to fall below $100k, for tourists when orbital facilities
exist to accommodate them.
As high volume flights are performed the 15 ton payload to LEO orbit would be $2-10 million per launch which would be $66/lb to $330/lb.
SABRE's heat exchanger, also known as a pre-cooler, is the engine's key
technology. Just before the engine switches to rocket mode at Mach 5,
the incoming air will have to be cooled from 1,832 degrees Fahrenheit
(1,000 degrees Celsius) to minus 238 degrees Fahrenheit (minus 150
degrees C), in one one-hundredth of a second, displacing 400 megawatts
of heat energy using technology that weighs less than 2756 pounds (1,250
kg).
The pre-cooler technology was successfully tested in 2012, and the
achievement was independently confirmed by ESA, on behalf of the UK
government.
Aerospace engineers have dreamed of a spaceship that can launch
like a plane, get to orbit, and land on a runway since the 1960s. A
British company, Reaction Engines Limited, wants to make that dream a
reality. REL’s sleek, winged spaceplane, called the Skylon, looks like
something out of the retro-futuristic visions of old magazine covers. The spacecraft is built to fly like a jet — at first The
uncrewed spacecraft is built to fly like a jet until it gets to an
altitude of about 92,000 feet at five times the speed of sound (3,800
miles per hour). Then rocket propulsion will shoot the Skylon to orbit
along with 15 metric tons of cargo. On return, it’s designed to glide
down to a waiting airport, rather like the Space Shuttle.
According to a recent economic analysis by REL – but with some
backstopping from independent consultancy London Economics – Skylon can
get a pound of mass to orbit for between $686 and $1,230 per pound,
depending on how optimistic the forecast. This is comparable to SpaceX’s
currently advertised rate of about $2,100 per pound for the Falcon 9
and $770 for the upcoming Falcon Heavy.
That would be a huge savings over the Space Shuttle, which was about $10,000,
according to NASA. (One reason NASA’s estimate is so high relative to
SpaceX or Skylon is not just that the Shuttle is expensive, but NASA has
to reveal their total costs. SpaceX is a private company, so estimating
what their actual costs are, as opposed to the price, is more
difficult).
Yet there are still big hurdles. Nobody has made a combined
jet-and-rocket design work before, let alone single stage to orbit.
Designing a propulsion system that can do it has been one of the biggest
obstacles – pure rockets or jet engines are one thing, but combining
them is another. And then there’s building something that flies under
conditions that give the most advanced designs a run for their money.
Compared to the spaceplane, building a Concorde was easy.
Breathing Air
The secret to getting their spaceplane aloft is the Synergetic
Air-Breathing Rocket Engine, or SABRE, a combination jet engine and
rocket. Initially it "breathes" air, functioning the way a jet engine
does: by igniting hydrogen fuel with the oxygen in the atmosphere. Once
the air gets too thin, it simply switches to using an onboard tank of
oxygen. Ordinarily, a jet engine can't operate at Skylon's speeds Ordinarily
a jet engine can’t operate at the speeds at which Skylon flies. The
fastest jet plane ever flown was the SR–71 "Blackbird," which hits three
times the speed of sound. Go much faster than that and the air coming
into the engine compresses and heats up – and the engine cooks. The
solution? Cool the air coming in.
"We are developing the key technologies for the SABRE engine," says
REL’s managing director Mark Thomas. "The most important is the heat
exchanger."
When air comes into the SABRE, it gets cooled down with liquid
helium. The helium has itself been cooled via an exchanger that uses the
liquid hydrogen fuel. Once the helium is done pre-cooling the air, it
gets heated again by the combustion of the hydrogen and oxygen, and that
energy drives the turbines in the engine. The combined mechanism saves
weight and allows the engine to work from a resting start.
The company plans to test the engines this year; the tests will be on
the ground, essentially firing them to see if they work as planned.
Mark Ford, head of propulsion engineering at the European Space
Agency, says there’s no reason the SABRE shouldn’t work."We saw no
technological or engineering showstoppers," Ford says. A 2011 report
from ESA said the idea is feasible.
While engines are the most important part of the craft, other
challenges still give experts pause. Heat is one. The Space Shuttle had
to be covered with tiles because most metals wouldn’t handle the heat
generated by re-entry. "We called it the crockery-covered spacecraft,"
said Ivan Bekey, a former head of the Advanced Concepts Office at NASA
and now a private design consultant. "If you’re flying at 25 times the
speed of sound then for a spaceplane the heat becomes a problem for the
ascent as well." "We called it the crockery-covered spacecraft."REL
says it plans to have two layers of skin on the Skylon, separated by a
small space. The outer layer will be made of ceramics, materials that
have been in development for decades and advanced since the Shuttles
were built, says Richard Varvill, technical director at REL. That will
help insulate the craft as it zooms through the upper atmosphere.
For re-entry, Skylon won’t come down in the same way as the Shuttle.
Varvill says instead of plunging into the atmosphere, Skylon will take a
gentler approach. "It has a more efficient aerodynamic shape," he says,
"with sharper leading edges on the wing. The overall heating is a lot
less than the Shuttle, though local hot spots on Skylon need local
cooling systems." The heating shouldn’t get to more than a few hundred
degrees centigrade, as opposed to the 1,200 degrees (or about 2,300
Fahrenheit) that the Shuttle would experience.
The last issue is where Skylon would land. The Space Shuttle landed
on long runways, but it could theoretically have used commercial
airports. Nineteen east coast airports were tapped for use if the
Shuttle had to abort, among them Bangor, Miami, and Atlantic City.
Skylon needs one 3.1 miles long (about five kilometers). Public runways
that long aren’t common: there are two in China, two in Russia, and one
under construction in Afghanistan. Another runway exists in France at a
military base. In the US, runways that long are all on military bases,
and the paved ones are all at Edwards Air Force Base.
Dyna Soar, artist's rendering, on an Atlas II (NASA/USAF)
(Dashed) Dreams of Flight
The aerospace landscape is littered with the corpses of failed and
unfunded projects. Spaceplane attempts go all the way back to the
two-stage X–20 Dyna Soar in the late 1950s. The program got cancelled in
1963. It was clear that rockets were simpler and cheaper to design and
build; the Dyna Soar wasn’t going to be ready to launch an astronaut
until the mid–1960s at best, while the Gemini program had already done
it. The Air Force also didn’t have a clear need to be putting people in
space. Aerospace is littered with the corpses of failed and unfunded projectsIn
the 1980s, the X–30, otherwise known as the National Aero-Space Plane,
was designed under the auspices of the Defense Advanced Research
Projects Agency – then-president Ronald Reagan mentioned it in the State
of the Union Address as a possibility for hypersonic transport. The
X–30 was a horizontal-launch design, which would reach a speed of about
18,500 miles an hour and achieve orbit. But after billions of dollars
over nearly a decade, the program was cancelled in 1993, never having
flown anything. In the 1990s there was the X–33 VentureStar, which would
have launched vertically. That too was cancelled.
Only the Space Shuttle (and the USSR’s Buran on a test flight) have
made it to orbit, and they both needed multiple stages and launched
vertically, because vertical launches minimize the amount of atmosphere a
spacecraft has to get through. The Shuttle was retired in 2011.
Other space agencies, such as the Indian Space Research Organization
(ISRO), are looking at spaceplanes. That said, the Shuttle’s
vertical-launch design is favored, though ISRO plans to push for a
single-stage-to-orbit design in 2025. The next tests are slated for this
year.
Ford, though, says the X–30 suffered from having to install separate
engines for each stage of flight. "Some of the engines aren’t running at
one time or another, and it’s effectively dead mass." The Skylon is
different in that respect, as it combines the engines into a single
unit.
Even so, SpaceX and Blue Origin are both working on reusable rockets
to get orbit, and as conventional, vertical-launch vehicles, they don’t
run into the problems that a spaceplane does. Blue Origin has soft-landed a rocket and SpaceX has also.
Artist's rendering of Skylon (REL)
Supply and Demand
REL will also have to raise a lot more money. Development costs
could, by the company’s own estimates, easily hit the $12 billion mark.
The company has raised a total of about $156 million from a combination
of private and government funding – there’s a long way to go. Skylon itself would be pricey to buildDemand for
launches might be another issue. The problem with Skylon is the sheer
number of flights you’d need to make it profitable, according to an analysis
by Ashley Dove-Jay, an engineer at Oxford Space Systems. There’s only
so many satellite communications companies, after all. And currently
there’s no reason for travelers to go into orbit. (Virgin Galactic plans
to pioneer the space tourism business and those trips will only be
sub-orbital). In the meantime, SpaceX could provide cheaper access to
space and bigger payloads per dollar. A similar problem plagued the
Space Shuttle – every launch was far more expensive than the uncrewed
rockets available, with estimates of per-flight costs at up to $1.2 billion. NASA underestimated the turnaround time for launches, and after the Challenger disaster, the Shuttle stopped taking commercial payloads
altogether. That limited the market for Shuttle launches to the ISS,
military, and science missions that required humans, a small piece of
the launch market.
Skylon itself would also be pricey to build. A single Skylon’s price
tag would approach that of a stealth bomber, and that isn’t something
that many airlines are likely to pay.
Yet with all these challenges REL is confident. It thinks it can play
a long game and that the technology will get developed. "We’ve made a
lot of technical inroads," Varvill says. "And we’re competing with
expendable rockets, a machine that is only used once."
"Reusability is the next big cost reduction," says Ford. And if the
engines work it might spark the demand for access to space. He also
likes it from a technical standpoint. "From an engineering perspective
it’s an obvious solution to a problem," he says. Rockets, in that sense,
are wasteful and inefficient. "I mean, what if someone said, ‘We’ll fly
you to London, and only you and the seats will get there?"
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