HIGH SPEED AIR BREATHING PROPULSION 2010 - AIAA Info

HIGH SPEED AIR BREATHING
PROPULSION 2010
Moving faster towards the Future
2010 was the year of the scramjet‐powered X‐51
Waverider, soaring at Mach 5 for over 3 minutes
and setting a new hypersonic flight world record.
DORA MUSIELAK
AIAA HSABP TC Communications
Airbreathing hypersonic propulsion entered a
new era in 2010. The 7.9‐m‐long X‐51A
WaveRider, powered by a Pratt & Whitney
Rocketdyne scramjet engine, made aviation
history on May 26 with the longest ever
scramjet‐powered flight. “This first flight test
brings aviation closer than ever to the reality of
regular, sustained hypersonic flight,” said Curtis
Berger, director of hypersonic programs at Pratt
& Whitney Rocketdyne. “We are very proud to
be part of the team that made this possible.”
The X‐51A program is a collaborative effort
of AFRL, DARPA, Boeing, and Pratt & Whitney
Rocketdyne. During its flight, the WaveRider
was carried beneath an Air Force B‐52 and
dropped from an altitude of 50,000 ft. A rocket
booster propelled the cruiser to a speed greater
than Mach 4.5, creating the supersonic
environment necessary for starting its flight.
Separating from the booster, the SJY61 scramjet
ignited, initially on gaseous ethylene; it then
transitioned to JP‐7 fuel.
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The achievement is significant, because this
is the first hypersonic flight by a hydrocarbon‐
fueled scramjet. “We are ecstatic to have
accomplished many of the X‐51A test points
during its first hypersonic mission,” declared
Charlie Brink, X‐51A program manager with
AFRL. Brink called the leap in engine technology
“equivalent to the post‐WW II jump from
propeller‐driven aircraft to jet engines.”
On that historic day, the X‐51 launched about
10 a.m. from Edwards Air Force Base, carried
aloft under the left wing of an Air Force Flight
Test Center B‐52 Stratofortress. Then, flying at
50,000 ft. over the Pacific Ocean Point Mugu
Naval Air Warfare Center Sea Range, it was
released. Four seconds later, an Army Tactical
Missile solid rocket booster accelerated the X‐
51 to about Mach 4.8 before it and a connecting
interstage were jettisoned.
The launch and separation were normal.
Then the SJY61 scramjet engine ignited, initially
on a mix of ethylene and JP‐7 jet fuel, then
exclusively on JP‐7 jet fuel, the same fuel once
carried by the SR‐71 Blackbird. The hypersonic
demonstrator vehicle reached an altitude of
about 70,000 feet and a peak speed of Mach 5.
The vehicle's fuel‐cooled engine, circulating
270 pounds of fuel serves both to heat the JP‐7
to an optimum combustion temperature and to
help the engine itself endure extremely high
operating temperatures during the long burn.
Without such active cooling, the temperatures
in the scramjet could reach 5,000°F, high
enough to melt virtually any metal on Earth.
Solving the cooling challenge is a major
AFRL/Pratt & Whitney achievement.
The much anticipated hypersonic flight did
not reach its maximum hypersonic speed and it
flew autonomously for only 200 seconds before
losing acceleration—its scramjet is designed for
Mach 6 and burn for 300 seconds. But as stated
by Joe Vogel, Boeing Director of Hypersonics
and X‐51A Program Manager, "This is a new
world record and sets the foundation for
several hypersonic applications, including
access to space, reconnaissance, strike, global
reach and commercial transportation."
The unmanned X‐51A WaveRider, powered by the
P&W Rocketdyne SJY61 scramjet engine, is designed
to ride on its own shockwave.
The X‐51A WaveRider was launched from beneath
the wing of a B‐52.
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We must add that this achievement is also
quite significant, as it is the first hypersonic
flight by a hydrocarbon‐fueled scramjet.
Hydrogen‐fueled scramjets have achieved
much higher speed. In fact, the previous record
was set by NASA's X‐43A, when its hydrogen‐
fueled scramjet engine burned for about 12
seconds in 2004; that experimental hyper‐
vehicle zoomed to Mach 9.8. And as much as
we like the clean burning of hydrogen, for some
applications, such as fighter aircraft and
missiles, hydrocarbon fuels are desired.
The successful flight of the first X‐51A
demonstrated the viability of hypersonic
vehicles. The advanced technologies in this
program is bound to stimulate the development
of hypersonic missiles and other military aircraft
in the near future, platforms able to travel long
distances quickly and close in on their targets so
fast they would be almost impossible to defend
against.
The X‐51A might also revive interest in hybrid
turbo‐scramjet engines, propulsion concepts
integrated into a new hypersonic vehicle that
would not depend on a booster rocket to
operate at the lower flight speeds. For example,
it might be possible to get the scramjet to light
up initially at speeds low enough to be
integrated with a regular afterburning turbojet
or with a detonation engine‐turbine hybrid
rather than booster rockets.
Such approaches would widen the prospects
for a number of applications including military
jets and reusable spaceplanes. For example, a
hypersonic jet fighter could take off from a
runway and accelerate to scramjet ignition
speed using an advanced jet engine, then
switch into scramjet mode and rush forward
into the hypersonic regime. This would
essentially be a modern, hypersonic update of
the incomparable SR‐71 turbo/ramjet spyplane,
the famous Mach‐3.5 Blackbird.
The performance of a turbo‐scramjet could
be further enhanced by the addition of a
detonation combustion augmenter for the
supersonic flight regime. This is because the
efficiency of the jet engines that powers today’s
military vehicles has approached its limit. But
detonation combustion offers the needed
performance improvement, resulting in a more
efficient propulsion system that could extend
vehicle range, cut fuel costs and reduce
emissions. Engineers at GE Global Research, for
example, have designed and built an eight‐
combustor version of a pulse detonation engine
(PDE) and integrated it with a conventional
turbine. This development effort is needed to
understand how to integrate a PDE in a real gas
turbine engine.
Having an efficient detonation engine‐
turbine‐scramjet, by integrating a rocket would
allow a spaceplane to take off from a runway,
gain the necessary speed and altitude still in the
air‐breathing mode, and then make the final
climb and acceleration to Mach‐25 orbital
velocity in the rocket mode. This would result in
a single‐stage to orbit spaceplane, one that
would carry significantly less oxidizer than
conventional two‐stage rockets.
Aerojet also made progress on advancing
scramjet technology in 2010. Under contract
with the U.S. Air Force Research Laboratory
(AFRL), the company completed ground testing
of a scramjet combustor, demonstrating a new
thermal management technique. Called core
burning, it forces the combustion flames away
from engine surfaces, thereby reducing overall
heat load. According to Aerojet’s patent by
Melvin Bulman, with core burning “a pilot for a
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scramjet provides a flame front whose arrival at
the wall of the scramjet combustor is delayed
thereby reducing combustor heat load. By
combining in‐stream injection of fuel with an
interior pilot and a lean (fuel‐poor) outer
annulus, the bulk of combustion is confined to
the scramjet combustor center. One such pilot
is for a two dimensional scramjet effective to
propel a vehicle. This pilot includes a plurality of
spaced apart struts separated by ducts and a
strut pilot contained within each strut. A second
such pilot is for an axisymmetric scramjet
engine has, in sequence and in fluid
communication, an air intake, an open bore
scramjet isolator and a scramjet combustor.”
Aerojet’s engineers expect that core burning
will require less fuel to cool the engine,
enabling scramjets to have more thermal
margin and to fly faster than with conventional
thermal management. During the tests, the
engine operated robustly at simulated Mach 3
to 5 flight conditions and at various simulated
altitudes and fuel injection settings. An Air
Force‐provided video camera recorded views of
the combustion process clearly showing the
flame holding and flame propagation processes
occurring from the combustor center, thereby
proving the core burning concept..
Aerojet’s core burning technology overcomes
the long‐standing challenge of flight speed
limiting thermal loads in the combustor. This
thermal management technique will be crucial
as the Air Force looks to progress from
“laboratory” engine scales to those of
operational sizes for long‐range, time‐critical
missiles and high‐speed military aircraft.
In 2010 Pratt & Whitney Rocketdyne and
Lockheed Martin also completed preliminary
design of an actively cooled Dual Mode Ramjet
combustor in support of the DARPA funded
Mode Transition (MoTr) Demonstrator
Program. This program seeks to ground test a
turbine‐based combined‐cycle (TBCC) engine
using hydrocarbon fuel. The MoTr program will
demonstrate transition from turbojet to
ramjet/scramjet cycle, the critical experiment
required to enable reusable, air‐breathing,
hypersonic flight. MoTr leverages previous and
on‐going advances in air‐breathing propulsion
technology, including the Falcon Combined‐
cycle Engine Technology (FaCET) and the Air
Force/DARPA High Speed Turbine Engine
Technology Demonstration (HiSTED) program.
The MoTr program will provide valuable risk
reduction for future flight test program
opportunities.
Aerojet’s Supersonic Sea‐Skimming Target
ramjet propulsion system successfully
completed the first flight test of the Coyote
High Diver supersonic target mission. The target
vehicle, developed by Orbital Sciences
Corporation with Aerojet’s solid‐fueled Variable
Flow Ducted Rocket (VFDR) engine, was rail‐
launched from the ground and boosted by a
rocket motor to ramjet‐takeover speed. Under
ramjet power, the system ascended to 35,000 ft
and reached Mach 3.3 cruise speed. At the end
of its 110 nautical‐mile‐long flight, the vehicle
executed a planned 40‐degree unpowered dive
to its objective.
The international community pushed
forward air breathing hypersonics as well.
Leading countries such as Australia, Brazil,
France, Japan, and Russia made significant
contributions to advance several technologies.
The following paragraphs provide highlights of
the progress made by other nations in 2010.
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Brazilian interest on High­speed
Air­breathing Propulsion
The Institute for Advanced Studies (IEAv), a
research center of the Brazilian Command of
Aeronautics, is developing two advanced high‐
speed air‐breathing propulsion technologies.
The IEAv’s Hypersonic Aerospace Vehicle,
named 14‐X (after the 14‐Bis developed by
aviation pioneer Alberto Santos Dumont),
initiated in 2005, is the first Brazilian project
Brazil’s Waverider Hypersonic Vehicle model
installed in the test section of the T3 Hypersonic
Shock Tunnel.
Brazil’s Hypersonic Aerospace Vehicle 14-X.
with the objective to design, develop, construct
and demonstrate a Mach 10 waverider in free
flight with its required scramjet technology.
The Mach 10 waverider Hypersonic Vehicle
model was experimentally investigated in
Brazil’s T3 Hypersonic Shock Tunnel of the Prof.
Henry T. Nagamatsu Laboratory of
Aerothermodynamics and Hypersonics.
Brazil’s IEAv is also developing the
Hypersonic Aerospace Vehicle, named DVPL
(Vehicle Demonstrator of Laser Propulsion).
IEAv Prof. Henry T. Nagamatsu Laboratory of
Aerothermodynamics and Hypersonics.
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Hypersonic Aerospace Vehicle DVPL (left). 2-D laser propulsion model installed in the test section of the T3
Hypersonic Shock Tunnel. Montage of the schlieren frames (left to right) for Mach 10 hypersonic flow and 1 GW
laser power (time between frames 10 μs)
Initiated in 2008 and in collaboration with the
U.S. Air Force Office of Scientific Research’s, the
DVPL is the first Brazil‐USA Laser Propulsion
Experiment with the objective to design,
develop, construct and demonstrate in free
flight laser propulsion technology.
A 2‐D Mach number 10 Laser Propulsion
Vehicle model designed and built by Prof. Leik
N. Myrabo from Rensselaer Polytechnic
Institute (Troy, NY), was experimentally
investigated in the T3 Hypersonic Shock Tunnel
(HST). Additional testing is expected in 2011.
Hypersonics Progress in France
France has a legacy of hypersonic air breathing
propulsion system assessments and technology
development dating back to the 1980s. In 2010,
MBDA and the French National Aerospace
Research Establishment (ONERA) pursued their
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R&T effort related to hypersonic air breathing
propulsion mainly thanks to French State
support but also with limited support from
European Union.
MBDA and ONERA are to receive by the end
of 2010, from French Administration, the
contract covering all the remaining part of their
flight testing program LEA. The goal of the LEA
program is to establish, apply and validate a
methodology for development of hypersonic air
breathing vehicles. The LEA experimental
vehicle should be flight tested in timeframe
2013‐2015 in the Mach number range 4 to 8 by
using existing Russian supersonic bomber, liquid
rocket booster and test range.
ONERA‐MBDA LEA vehicle
The first test series have been achieved in
the new METHYLE test facility providing
capability to simulate up to Mach 7.5 flight
conditions for large scale direct connected pipe
test with test duration up to 1000s. In parallel,
the upgrade of the ONERA S4Ma wind tunnel
has been pursued to provide a large scale Mach
6 free jet test capability which will be used for
LEA program in spring 2011.
Design activities were performed in the
frame of the European LAPCAT2 studies related
to high speed transport system. MBDA and
ONERA contributed to the design challenge of a
Mach 8 system.
Hypersonics Advances in Japan
JAXA (Japan Aerospace Exploration Agency)
conducted RBCC model combustion
experiments at Mach 11 conditions in the High
Enthalpy Shock Tunnel (HIEST), following sea‐
level static, Mach 4 and Mach 6 tests. The
rocket engine in the RBCC produces most of the
thrust, while the supersonic combustion engine
assists in production of thrust. A detonation
tube was used in the test to supply large
amount of combustion gas as rocket exhaust in
a short period.
Inside JAXA’s M11 experimental RBCC model. It has
two rocket nozzles, connecting to a detonation tube
by a pipe below.
JAXA’s horizontal firing test of pre‐cooled turbojet
engine
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JAXA’s vertical firing test of pre‐cooled turbojet
engine
Researchers at JAXA also plan a Mach 2 flight
experiment of the hypersonic pre‐cooled
turbojet engine model using a stratospheric
balloon. Ground firing tests were already
conducted with both horizontal and vertical
attitude to evaluate the effect of gravity force in
a free‐fall flight. The starting characteristics of
the air‐intake were also obtained in a
supersonic engine test facility.
Russia Hypersonics Success
Successful tests of a large‐scale scramjet model‐
demonstrator integrated with an airframe
simulator of an experimental hypersonic flying
vehicle (HFV) were run for the first time at the
Central Institute of Aviation Motors, Russia, in
April, 2010. The tests were conducted within
the framework of the Federal Research Program
(FRP) “National Technological Base” (NTB).
The demonstrator tests followed successful
complex thermo‐gasdynamic studies of small
scale integrated models of HFV “propulsion +
airframe” and their components, as well as
launching tests of a powerful high‐altitude
hypersonic rig of 1.2 m nozzle diameter at the
end of March, 2010 during its technical
upgrading within the framework of FRP “NTB”.
The exhauster machines of altitude‐compressor
station provide for vacuum in the rig working
section. A generator of high‐enthalpy air flow
made within a state contract with the Rosnauka
produces the required total working gas
parameters appropriate to flight hypersonic
speeds. The rig allows studying the working
process in integrated experimental “engine +
HFV” objects with simulation of hypersonic
flight conditions.
Russia’s HFV Model
Tested rig model was displayed in the International
Aerospace Salon MAKS‐2009
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Scramjets/Rocket­powered
Space Launchers
Engineers at NASA KSC proposed a scramjet‐
powered vehicle that can be rail‐launched all
the way to orbit
In the proposed 10‐year plan, a wedge‐
shaped vehicle powered by a scramjet engine is
launched horizontally along an electrified track,
or gas powered sled, carrying a pod or
spacecraft destined for low Earth orbit (LEO).
The scramjet would fly the vehicle to Mach 10
to reach the upper edge of the atmosphere
where a small rocket would fire off and propel
the vehicle into orbit. The hypersonic craft
would come back and land on a runway by the
launch site.
The so called Advanced Space Launch
System, comprised of railgun, scramjet, and
rocket, was recently unveiled by Stan Starr,
branch chief of the Applied Physics Laboratory
at Kennedy in Florida. He indicated that the
system counts on the availability of a number of
existing technologies. His team is already
working on a rail launcher using gas propulsion,
and they are applying for funding under several
areas, including NASA’s technology innovation,
to develop and further mature the needed
technologies. If successful, this new launch
approach can revolutionize access to space.
There are some technical challenges to
overcome first. According to the NASA team, to
launch on an electrified track, for instance, the
track would have to withstand at least 10 times
the speeds commonly seen on tracks used for
roller coasters. Roller coasters typically run
about 60 mph (100 km/h).
Electrified rail assist to Mach 1.5 (NASA image courtesy of S. Starr, KSC)
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Proposed NASA eLauncher Configuration (Ref. S. Starr, NASA KSC)
NASA is also investigating other methods of
powering a track‐launched vehicle. Engineers
with NASA’s Marshall Space Flight Center in
Huntsville, AL, have already tested a prototype
track‐based system that uses magnetic
levitation to accelerate vehicles to launch
speeds.
There are several studies underway to
examine new launch architectures. The USAF,
for example, is looking for architectures to
eventually replace the existing EELV’s (Delta IV
and Atlas V) which involve vertical rocket launch
of a hypersonic stage. DARPA is studying
scenarios that involve runway take off. All of
these studies are based on the belief that
practical scramjet propulsion is going to provide
a design alternative in the 20‐year time frame
so that reusable air breathing launch stages can
be built and used routinely. The question seems
to be, “what launch architecture optimizes the
contribution by air breathing?” We know that
the final stage into orbit has to be a rocket. We
also know that the higher the initial velocity,
the lower the mass of the air breathing
propulsion system. For example an integrated
vehicle taking off from a runway will require
large low speed turbines in addition to high
speed turbines, ram and scramjet engines (a lot
of engines). According to Stars, if we can launch
a vehicle from a rail with an initial velocity of
Mach 0.5 we can decrease the size of the low
speed turbines, but they are still required
(although we do save propellant, wing mass,
landing gear mass and other benefits). If we
launch at Mach 1.5 we can launch with high
speed turbines plus RAM/SCRAM. We also incur
high dynamic pressures (increased structural
mass) and environmental effects from sonic
boom.
So Starr’s basic concept is to launch at a
higher velocity than previous studies
considered, thereby significantly simplifying the
propulsion system and reducing weight. Of
course those benefits must be weighed against
a more complex total system (track) and the
associated costs.
As for the scramjets, KSC engineers will draw
from the experience gained through recent
scramjet flight demonstration testing, including
NASA’s X‐43A and the U.S. Air Force’s X‐51,
both of which have shown that scramjets can
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achieve the required speeds for the proposed
rail launcher.
Starr and his NASA KSC engineering team
proposed a 10‐year plan that would begin with
launching a drone similar to those used in the
ongoing Air Force tests. More‐advanced models
would then follow, with the goal of developing
a vehicle that can launch a small satellite into
orbit.
The proposed Advanced Space Launch
System is not meant to replace NASA’s space
shuttle fleet, which is schedule to retire next
year, or any other manned spacecraft program,
Starr said. But if this system is proven successful
for unmanned launches, Starr believes that it
could eventually be adapted to carry
astronauts.
Finally we must add that not only do we
need to advance hypersonic air breathing
propulsion for hypersonic missiles, military
superfast vehicles, and reusable Earth‐to‐space
launchers, now we must work to develop
vehicles that can move at hypersonic speeds in
extraterrestrial planetary atmospheres.
In fact, NASA expects more research in this
area and amended its announcement,
“Research Opportunities in Aeronautics 2010,”
to include new topics in support of the agency’s
Hypersonics Project.
With the amendment, the Hypersonics
Project of the Fundamental Aeronautics
Program calls for proposals about enabling
technologies and development of a new pool of
expertise in two primary areas of interest.
These include air‐breathing access to space and
entry, descent and landing of high‐mass
vehicles in planetary atmospheres.
Looking Ahead
The complex requirements of faster vehicles
will continue to demand advancements in
hypersonic propulsion. The spectacular flight of
the X‐51A waverider brought scramjet
technology a major step closer to practical
reality, getting farther into the future.
Acknowledgements
The author is grateful to the following
people for providing information for this
article:
• Nancy Colaguori, Pratt & Whitney
Rocketdyne
• Tim O’Brien, Aerojet
• Stan Starr, NASA KSC
• Paulo Gilberto de Paula Toro, IEAV,
Brazil
• Takeshi Kanda, JAXA, Japan
• Francois Falempin, MBDA, France
• V. Vinogrodov, CIAM, Russia
More information about the activities of the
AIAA High Speed Air Breathing Propulsion
Technical Committee (HSABP TC) at
https://info.aiaa.org/tac/PEG/HSABPTC/default.
aspx
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