1. Current State
1. Page 4
i. During these four decades, the lack of investment in hypersonic test technologies
and facilities has prevented the testing community from keeping pace with the
testing needs of hypersonic S&T programs and projected system applications.
ii. Reasonably good hypersonic perfect gas aerodynamic wind tunnels exist today, but
none simulate the real-gas and aerothermal effects encountered in flight at Mach
numbers above 8. Aerothermal test capability is currently limited to perfect gas
wind tunnels and nonequilibrium flow shock tunnels capable of gathering heattransfer data.
2. Page 8
i. Current technology involves extensive infrastructure that is not effectively
integrated. This infrastructure typically consists of control systems, test and
checkout equipment, mission planning systems, and flight safety planning and
operations.
3. Page 10
i. Dynamic staging/store separation is done rather routinely using today’s technology.
4. Page 13
i. The large engine test facilities are limited to Mach 3.2, yet turbine engine R&D
programs predict future engine performance to Mach 4 and above.
ii. Although short run times may be useful for evaluating performance at discrete
design points, seconds, minutes, or tens of minutes of run time will be required for
operability and durability testing.
iii. The primary propulsion test capability that exists above Mach 8 currently is
relatively small impulse (shock) tunnels where the test time is of the order of
milliseconds and the test medium is usually not clean air.
5. Page 14
i. Perfect-gas, relatively cold-flow, wind tunnel test capability exists in the U.S. to
about Mach 16.
6. Page 15
i. At present, aero-optic testing is limited to cold-flow (perfect gas) and impulse wind
tunnels.
ii. Developers of missiles favor a full-scale test in highly productive facilities and will
acquiesce to flight duplication enthalpies that can be provided only by very short
run time facilities ( shock/impulse wind tunnels).
iii. High-speed impact testing has been limited to speeds of less than 7km/s by
performance limitations inherent in the two-stage light-gas guns, which are
generally used to accelerate impact models.
iv. Sled track velocity limits are currently Mach 9.4.
7. Page 16
i. Existing ground-test facilities can provide partial simulation. Perfect gas wind
tunnels are used to measure heat-transfer coefficients (up to about Mach 16)
although they do not provide the enthalpy required for the full heating rates.
Impulse tunnels can provide the correct Mach number and enthalpy but for very
short test times.
ii. Ballistic ranges can provide the correct environment but for short test times.
Electric arc heaters can provide high enthalpies but incorrect aerodynamics. All of
the above may have scale shortcomings.
8. Page 18
i. Standardization Decision Support Tools – The development of improved suites of
tools is required to aid in the decision making process. The current tools are mostly
stand-alone and are not necessarily standardized across the ranges. The vision
would be to have an automated suite of tools integrated with flight prediction
models, IIP models, debris dispersion models, and flight simulators.
ii. Currently, insufficient in-house technical expertise and analysis tools are available to
support hypersonic flight-test planning and engineering analysis activities. These
activities include test engineering, test operations, and M&S capabilities over
diverse flight regimes and test environments.
9. Page 19
i. Current data storage media will not support future HS/H system requirements, and
data distribution requirements for future hypersonic missions will exceed the
capability of current distribution networks.
ii. Metric tracking of platforms fling at hypersonic speeds are limited by present
tracking system slew rates and response times, which are too slow to maintain
track.
iii. In general, the current tracking capability relies on fixed-location, ground-based
metric radars with C-band beacons aboard flight vehicles and inertial measurement
unit (IMU) data in the telemetry stream.
iv. …current capability, which involves manual data collection, data relay via voice, and
table-top-tokens display.
v. Presently no other compatible alternatives exist other than using legacy multirange
specific data acquisition and reduction and distribution systems not adhering to
data exchange standard and interfaces.
10. Page 20
i. At present, measurements for pressure, temperature, and heat flux are available.
ii. Plasma-generated attenuation denies the capability to pass data between
hypersonic vehicles operating at Mach 10 and above and mission control facilities.
iii. The Intercontinental Ballistic Missile (ICBM) flight-test community has been
transmitting its telemetry data without encryption for 30 years, so that capability
and technology exists today.
2. Future/Vision State
1. Page 4
i. Some of the desired test facilities must themselves be supported by research to
investigate new approaches for energy addition and materials/cooling techniques to
permit containment of the required high-pressure, high-temperature test gases.
ii. Small electric arc tunnels and vitiated air test mediums exist and can be used to
conduct material testing of relatively small samples. The primary aeropropulsion
hypersonic ground-test facilities available in the U.S. today consist of impulse
facilities providing milliseconds of test time, blowdown vitiated facilities providing
seconds to minutes of test time (but without a clean-air medium), small research
facilities with clean air, and small electric arc tunnels.
2. Page 15
i. A facility with flight enthalpy duplication capabilities and run times of the order of
seconds does not presently exist, but such a facility would provide added transient
testing capability at flight enthalpies. The need for highly productive cold-flow
facilities will continue to exist as before.
3. Page 16
i. HS/H aircraft systems that operate within the atmosphere for minutes and hours
will require an entirely new type of testing with associated testing capability. It is
common for new aircraft structures to be subjected to simulated flight loads
reproduced via mechanical means. With the high-speed aircraft, not only will the
flight loads be increased, but also the structure will experience internal loading
produced by thermal stresses. The vehicle’s cooling system must accommodate the
very high aircraft leading-edge temperatures and the propulsion system. These
temperature extremes will defy analytical solution in the complex structures. It will
be necessary to test major full-scale aircraft components in nonflow ground-test
facilities that produce both external and internal loading. Such a facility, which was
being planned in the NASP program prior to program cancellation, is critical for
production of manned long-range hypersonic aircraft.
ii. Consequently, new and upgraded range tracking and instrumentation will be
needed. This section discussed in detail the new capabilities and resources that will
be needed for hypersonic flight testing.
iii. To fulfill the purpose of national space policy and national space transportation
policy, suitable hypersonic corridors for air-launched, generic, combined-cycle, and
hypersonic vehicles need to be identified.
4. Page 17
i. Over-land flight capability is critical for the viability of future HS/H testing and
operations for military access to space and hypersonic vehicles. This requirement
becomes especially critical for reusable systems that require contingency and abort
options for the vehicle in the case of vehicle anomaly, both manned and unmanned.
ii. A proposed solution would still look at developing a land/sea range capability for
hypersonic air vehicles, as well as developing viable recovery system (e.g., chute)
options – a gap that still exists.
iii. A proposed solution would be to continue to analyze and develop an Over-theHorizon Flight Termination System (OTH FTS).
5. Page 18
i. Standardization Decision Support Tools – The development of improved suites of
tools is required to aid in the decision making process. The current tools are mostly
stand-alone and are not necessarily standardized across the ranges. The vision
would be to have an automated suite of tools integrated with flight prediction
models, IIP models, debris dispersion models, and flight simulators.
ii. The next generation of hypersonic vehicles (missiles and aircraft) will require a new
generation of hypersonic flight-test tools and test methodology to support full
spectrum flight-test and mission planning.
6. Page 19
i. Closing this gap will require developing increased data processing capabilities in
mission control rooms and data centers, transitioning from legacy data storage
media to dynamic, interactive data transmission control and display systems, and
reconfiguring data transmission methodologies.
ii. The long-term goal is to interface with other space and air traffic management
systems and to have seamlessly integrated global operability for GPS and IMU
metric tracking. The key step here (for tracking) in the near- and mid-term is to
evolve to using GPS and IMU as part of a space-based range. The use of other
mobile range assets such as high-altitude airships (HAA) and unmanned aerial
vehicles (UAVs) to supplement space-based coverage is also envisioned.
iii. The near-term desire is to automate the collection, transfer, and integration of
surveillance data. The long-term goal is to include integrated, space-based
surveillance and real-time situational awareness within selected regions worldwide.
7. Page 20
i. A proposed solution would need to determine the feasibility of nonintrusive
instruments to measure products of combustion and/or velocity, as well as set up a
feasibility study of more advanced nonintrusive instruments to measure in-stream
products of combustion and/or velocities.
ii. A proposed solution would involve a scientific study to reduce plasma-generated
attenuation for better data reception.
iii. A proposed solution would look at redesigning how data are “encrypted” to meet
security standards. Raw unannotated/nondescriptive data are unclassified. Unless
the parameter name and scale factor to apply to each measurement are known, the
data cannot be comprised.
iv. A real-time imaging tracking instrumentation system capability is required to
acquire and track airborne vehicles that are air/ground launched with the capability
of achieving hypersonic velocities at exoatmospheric altitudes.
3. Gap challenges/issues
1. Page 2
i. The challenges for applying M&S to hypersonic flight conditions encompass
deficiencies in modeling turbulence, flow separation, aerothermochemistry, plasma
interactions, and conjugate heat transfer.
ii. The flight condition simulation capabilities required for the transformational HS/H
systems envisions far exceed current ground test capabilities with respect to:
1. Sufficient run times to achieve necessary thermal equilibrium conditions
2. Sufficiently high enthalpy conditions to properly simulate propulsion and/or
heat-transfer phenomena
3. Flow medium and flow quality to provide sufficiently accurate simulation for
scale-to-flight conditions
4. Test facilities with sufficient scale to simulate a fully integrated
airframe/propulsion system
2. Page 4
i. Some of the desired test facilities must themselves be supported by research to
investigate new approaches for energy addition and materials/cooling techniques to
permit containment of the required high-pressure, high-temperature test gases.
ii. Reasonably good hypersonic perfect gas aerodynamic wind tunnels exist today, but
none simulate the real-gas and aerothermal effects encountered in flight at Mach
numbers above 8. Aerothermal test capability is currently limited to perfect gas
wind tunnels and nonequilibrium flow shock tunnels capable of gathering heattransfer data.
iii. Also, there is not a capability to propulsion mode transition testing at supersonic
and hypersonic Mach numbers.
3. Page 7/8
i. Ideally, hypersonic systems would be developed with the same testing rationale as
today’s supersonic systems. However, the higher the system performance Mach
number, the larger the gap in the ability to test the system using today’s facilities.
For the higher Mach numbers, it will likely be technically impossible to design and
build ground-test facilities that will concurrently provide both adequate simulation
of flight conditions and extended run times.
4. Page 8
i. The research flights, though successful in providing scramjet operation at
hypersonic speeds, have shown deficiencies in areas such as micro-instrumentation
development and the difficulty in calibrating various instrumentation components
to the vehicle’s operating speed.
ii. Improved monitoring capability is needed. Sensors are a critical component not
only for assessing health and status, but also for understanding a vehicle’s
performance characteristics. Several drawbacks exist in today’s sensor systems.
First, they are generally intrusive. Second, they are less reliable than the hardware
that is being monitored. Third, most need manual calibration. Fourth, they are
unable to detect when the output is degraded or has failed. Finally, they cannot
detect off-nominal reading caused by the effects of failures in other parts of the
system.
iii. Gaps between current capabilities and required capabilities were the basis for
determining a HS/H T&E capability requirement roadmap.
5. Page 13
i. The large engine test facilities are limited to Mach 3.2, yet turbine engine R&D
programs predict future engine performance to Mach 4 and above.
ii. Although short run times may be useful for evaluating performance at discrete
design points, seconds, minutes, or tens of minutes of run time will be required for
operability and durability testing.
iii. This type of vitiated air test capability is limited to about Mach 8 simulated flight
total temperature.
iv. The effects and limitations of combustion-vitiated testing, development of clean air
test facilities below Mach 8, definition of needed facility runs times, and
definition/development of test capabilities above Mach 8 are all test facility
technology gaps that must be addressed.
6. Page 14
i. Development of a programmed accelerating and decelerating hypersonic propulsion
system is considered to be a challenge for both the engine designer and the test
facility designer. Conceptual approaches to multimode propulsion systems need to
be defined to assist test facility designers.
ii. …improvements in inlet airframe integration and nozzle after-body test capabilities
are needed, especially for large-scale (aircraft size) testing where geometric fidelity
is needed and can only be achieved at reasonably large scale.
iii. Thus, there is a need for real-gas flight simulation test capability, and/or analytical
procedures are needed to correct data taken from perfect gas and nonreal-gas wind
tunnels to predict flight results.
7. Page 15
i. Hypersonic wind tunnel productivity is an issue, especially above Mach 10. For
production development testing, thousands of data points are typically needed to
support aircraft design. Existing blow-down wind tunnels provide seconds to
minutes of test time. Impulse tunnels operate for milliseconds, and only a limited
number of these facilities exist. One set of data points per run is generally available
in these cases. Productivity must be a major consideration when selecting a
solution.
ii. As with the case of aerodynamic testing, test time is an issue and a gap for any
testing above Mach 10.
iii. Test article thrown weight, velocity, and fidelity are inadequate for the projected
weapon systems. Sled tracks are limited in velocity, while gas guns are limited in
weight and scale.
8. Page 16
i. …there is a gap in providing the correct flow chemistry, which may be addressed
with M&S. There is also a gap in providing sufficient scale for testing. If gaps are
filled for air-breathing propulsion, the aerothermal gaps will also be closed.
ii. For advanced hypersonic vehicle demonstrators, some shortfalls exist in our range
infrastructure to adequately validate their applicable technologies.
9. Page 17
i. There is a gap in the ability to cost-effectively recover expendable hypersonic
vehicles for data analysis of flight vehicle and propulsion system materials for
vehicles launched over the water.
ii. A proposed solution would still look at developing a land/sea range capability for
hypersonic air vehicles, as well as developing viable recovery system (e.g., chute)
options – a gap that still exists.
10. Page 21
i. A flight-test gap exists in the capability to air-launch the heavier hypersonic missile
systems, support technology demonstrations, and provide flight-test support for
hypersonic and Access-to-Space vehicles.
ii. A major cost-reduction gap lies in advanced ground support systems for hypersonic
vehicles.
iii. There is currently a gap in the capabilities for testing hardware in the loop, including
needs to have communication links to the launch and landing sites, control room,
and range for checkout and validation of communication links prior to launch.
4. Recommendations
1. Page 10
i. A “new” look at the aeroflow-field physics processing methods – or even the
rudimentary programming language to make the models more readily processable –
might be a good pursuit in the near term.
5. Other
1. Page 3
i. One of the major reasons for the demise of the ambitious NASP program, as stated
by the Scientific Advisory Board in a postmortem analysis, was a lack of ground-test
facilities to develop the needed system capabilities.
2. Page 4
i. …lack of adequate ground-testing capability has severely handicapped hypersonic
programs in the past and will continue to do so until the needed test resources are
made available.