Stratolaunch Air-Launched Hypersonic Testbed

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Stratolaunch Air-Launched Hypersonic Testbed
Stephen Corda1, Curtis M. Longo2, and Zachary C. Krevor3
Stratolaunch Systems Corp., Seattle, WA, 98104, USA
Stratolaunch Systems is exploring the development of aerospace vehicles and technologies
to fulfill several important national needs, including the need for reliable, routine access to
space. This exploration includes the need to significantly advance the nation’s ability to design
and operate hypersonic vehicles. Aligned with these goals, Stratolaunch is in the early
development stages of an unmanned, autonomous, reusable hypersonic testbed, to be air-
launched from the Stratolaunch carrier aircraft, the largest aircraft, by wingspan, ever built.
Powered by a Stratolaunch-developed liquid-propellant rocket engine, the Stratolaunch
hypersonic testbed is capable of accelerating to hypersonic speeds, then gliding to an
autonomous, horizontal landing on a conventional runway. The Stratolaunch hypersonic
testbed offers heretofore unobtainable hypersonic test capabilities, which may provide the
quickest and most efficient path for transitioning hypersonic technology from the research
environment to operational applications. The Stratolaunch carrier aircraft is described,
including its nominal mission parameters and payload-carrying capabilities. Conceptual
design details of a Mach 10-class Stratolaunch hypersonic testbed are discussed, including its
aerodynamics, performance, propulsion system, and sub-systems packaging. Plans for the
development of a smaller, Mach 6-class hypersonic testbed are also briefly described.
I. Nomenclature
d = distance, nmi
H = altitude, ft
M = Mach number
q = dynamic pressure, lb/ft2
t = time, sec
Greek Symbols
α
= angle-of-attack, deg
γ
= flight path angle, deg
Acronyms
ASE = airborne support equipment
CFD = computational fluid dynamics
COTS = commercial-off-the-shelf
GNC = guidance, navigation, and control
MCC = mission control center
MLV = medium launch vehicle
MR = mobile range
NASA = National Aeronautics and Space Administration
PGA = Paul G. Allen
SATCOM = satellite communication
1 Senior Technical Fellow-Hypersonics, Engineering Department, Senior Member.
2 Principal Engineer-Hypersonics, Engineering Department, Senior Member.
3 Vice President of Engineering, Engineering Department, Senior Member.
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22nd AIAA International Space Planes and Hypersonics Systems and Technologies Conference
17-19 September 2018, Orlando, FL 10.2514/6.2018-5257
Copyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
AIAA SPACE Forum

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II. Introduction
TRATOLAUNCH Systems Corporation was formed in 2011 by Microsoft co-founder Paul G. Allen as a privately-
funded aerospace company. Paul Allen has emerged as a pioneer in the aerospace field, pushing the boundaries
of what is possible, with such ventures as SpaceShipOne, achieving the first manned private spaceflight, and the
Stratolaunch carrier aircraft, the first stage of a space transportation system utilizing the largest aircraft, by wingspan,
ever built. Following in this tradition of aerospace trailblazers, Stratolaunch is pursuing a portfolio of aerospace
vehicles, which may be air-launched from the carrier aircraft. The Stratolaunch air-launched portfolio include the
commercial Pegasus XL solid propellant rocket, a medium launch vehicle (MLV), a space launch vehicle, and a
hypersonic aerospace plane and testbed (Fig. 1). The main propulsion for all of these vehicles are Stratolaunch-
developed liquid propellant rocket engines.
Fig. 1 Stratolaunch portfolio of launch vehicle solutions.
The large payload-carrying capability, in both size and weight, of the carrier aircraft, opens up the design space for
potential launch vehicles, including a new hypersonic testbed. With its unique ability to carry very large, heavy-weight
vehicles and its mobile range capability, the Stratolaunch carrier aircraft has the potential to serve as a launch platform
for a new class of hypersonic and space vehicles with few constraints on size, shape, volume, and launch location.
Stratolaunch has recently evaluated several hypersonic vehicle configurations that may be compatible with the
carrier aircraft. In particular, Stratolaunch has focused on the design of an air-launched testbed capable of hypersonic
flight at speeds in excess of Mach 10 with potential operations in the coming years. This hypersonic testbed could
provide risk reduction and technology maturation for hypersonic and space-launch vehicles in areas such as
aerothermodynamics, air-breathing propulsion, guidance, navigation, and control (GNC), instrumentation, high-
temperature materials, design tool validation, and other areas. In addition, there are several areas of interest that are
specific to captive-carry and air-launch operations of hypersonic and space vehicles, such as airborne propellant
management and mobile range considerations.
III. Stratolaunch Carrier Aircraft
The Stratolaunch carrier aircraft (Fig. 2) is the first stage of an air-launch space access system that seeks to make
spaceflight more flexible and routine. The aircraft is the largest all-composite aircraft ever built, with a 385-foot
wingspan that makes it the world’s largest aircraft by wingspan. The aircraft has a distinctive twin-fuselage, twin-
empennage configuration, with a high-mounted wing. The pressurized cockpit is located in the right fuselage, while
payload support equipment is housed in the left fuselage pressurized cabin. Selected dimensions of the carrier aircraft
are given in Fig. 3. Some interesting size comparisons are shown in Fig. 4. With a wingspan greater than the height
of the Saturn V rocket, the first flight of the Wright Brothers Flyer I could have been completed within a distance less
than half the carrier aircraft wingspan. Selected specifications of the carrier aircraft are provided in Table 1.
S
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Fig. 2 Stratolaunch carrier aircraft.
Fig. 3 Carrier aircraft dimensions.
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Fig. 4 Carrier aircraft size comparison.
Table 1 Selected specifications of the Stratolaunch carrier aircraft.
Parameter Specification
Wing span
385 ft
Length
238 ft
Tail height
51 ft
Propulsion
6 × PW4056 engines
Maximum takeoff weight
1,300,000 lb
Payload capacity
545,000 lb
Operational range
1,000 nm
Many of the carrier aircraft systems are “borrowed” or modified from those on the Boeing 747 jumbo aircraft,
including its six Pratt & Whitney PW4056 turbofan jet engines, each producing approximately 56,000 pounds of sea
level thrust. The landing gear, adapted from the Boeing 747, are comprised of two retractable nose gear, one in each
fuselage, and six retractable main gear, three in each fuselage. Aircraft control is accomplished using an irreversible
flight control system that mechanically signals and hydraulically actuates ailerons, elevators, and rudder control
surfaces.
The twin fuselage configuration is designed for the carriage of large vehicles or payloads below the center wing
section, between the fuselages. The maximum gross weight of a vehicle or payload that may be carried on the center
wing pylon is over 500,000 pounds. Commensurate with this large weight-carrying capability, the size of the payload
may be quite large, as shown in Fig. 5. Of course, each payload is unique and will require analyses and testing to
verify that the captive-carry flight of the payload meets both performance and safety requirements. Typical analyses
may be related to aerodynamics, stability and control, flutter, and other areas. The safe release and dynamic separation
of the payload must also be verified prior to flight.
Many payloads require support equipment to maintain the payload and its systems at the proper conditions during
captive-carry flight. This airborne support equipment (ASE) may be carried in the underwing pylon itself and in the
left aircraft fuselage cabin. The pylon volume is unpressurized, while the left fuselage cabin area is pressurized and
temperature controlled. ASE may include equipment for environmental control, electrical and avionics equipment,
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electrical harnesses and fluid routing components, communication and data acquisition equipment, and pressurized
tanks and systems for cooling, purging, and pressurization.
Fig. 5 Approximate payload cross-sectional accommodation zone.
At its maximum gross takeoff weight of 1.3 million pounds, the carrier aircraft has an operational range of
approximately 1,000 nautical miles, providing the launch flexibility to insert multiple payloads into space in various
orbits and inclinations, all launched during a single airborne mission. As shown in Fig. 6, a typical air-launch flight
profile starts with takeoff from a conventional runway, such as at the Mojave Air & Spaceport, Mojave, California,
followed by a climb to a pre-determined launch altitude, Mach number, and geographical location. Once reaching the
release conditions, the carrier aircraft may perform a pull-up maneuver, increasing the flight path angle of the launch
vehicle, prior to release. Typical release conditions are a Mach number of 0.63 at an altitude of 30,000 feet. After
release from the carrier aircraft, the launch vehicle ignites its propulsion system and ascends to orbit. The carrier
aircraft then returns to land at the departure airport.
Fig. 6 Typical carrier aircraft air-launch mission profile.
The carrier aircraft has the ability to perform air-launch operations from almost anywhere on the globe. For
maximum flexibility, these air-launches are not tied to communication and data handling facilities and equipment at
ground-based launch ranges. Therefore, the carrier aircraft has a unique mobile range (MR) and satellite
communication (SATCOM) capability, providing an independent, airborne launch range.
Stratolaunch maintains a mission control center (MCC) for air-launch operations at the Mojave Air & Space Port in
Mojave, California. Using the MR-SATCOM system, carrier aircraft flight operations and air-launches can be
monitored and controlled from the Mojave MCC from almost anywhere in the world. A critical component of this
concept is the mobile range autonomous flight terminal system, which enables launch vehicle abort capability without
the need for a ground-based command.
As of this writing, completion of the carrier aircraft assembly and testing is ongoing in Mojave, California. The first
taxi test of the carrier aircraft at the Mojave Air & Space Port was successfully completed on 17 December 2017.
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IV. Stratolaunch Hypersonics
In the following sections, insight is provided into the Stratolaunch hypersonics initiatives and the potential benefits to
space launch and hypersonic vehicles. Some of these technology areas are discussed as they pertain to potential test
capabilities on a Stratolaunch hypersonic testbed.
Two Stratolaunch hypersonic testbed development projects are highlighted. The Stratolaunch Mach 10-class
hypersonic testbed, the Hyper-Z, is described, including its design requirements and potential missions. Details of the
Hyper-Z propulsion system, sub-systems packaging, and integration with the carrier aircraft are discussed. Selected
results from aerodynamic and performance analyses are also presented. Finally, plans for the development and flight
test of a smaller, Mach 6-class hypersonic testbed, the Hyper-A, are described.
A. Stratolaunch Hypersonic Initiatives
Stratolaunch is investigating a variety of space launch vehicle configurations, all of which must operate in the
hypersonic flight regime. These space launch vehicles share many technologies with vehicles that are designed to
accelerate or cruise at hypersonic speeds within the atmosphere. Some of these technology areas are listed in Table 2,
where the technology applicable to each type of vehicle is noted. As can be seen, there is considerable overlap between
the technologies that may benefit a hypersonic accelerator or cruiser and a space launch vehicle. Through the use of a
reusable hypersonic testbed, Stratolaunch seeks to validate technologies and reduce risk related to the design and
operation of both space launch and hypersonic vehicles.
Table 2 Possible technology areas benefiting from a hypersonic testbed.
Technology Area Technology Detail
Hypersonic
Vehicle
Space Launch
Vehicle
Aerothermodynamics and
flow physics
Boundary layer transition
X
X
Shock and flow structure interactions
X
X
Captive-carry and air-
launch operations
Mobile range
X
X
Autonomous, horizontal landing
X
X
Airborne servicing equipment
X
X
Rocket propulsion
Liquid rocket engine development
X
Cryogenic tank development
X
Cryogenic propellant management
X
Hypersonic air-breathing
propulsion
Air-breathing inlets & flow paths
X
Supersonic combustion
X
Aft-body and nozzle flows
X
Combined cycle flow paths
X
Plasma control
X
Instrumentation
Flight test instrumentation and sensors
X
X
Integrated vehicle health management
X
X
High-temperature
materials
Thermal protection systems
X
X
Transpiration cooled leading edges
X
X
Flight controls and
trajectory
Actuators
X
X
Autonomous control and GNC
X
X
Flight path design and optimization
X
X
Design tools
CFD modeling and validation
X
X
Captive-carry and release modeling
X
X
Technology areas of commonality between the hypersonic and space launch vehicles, which may be investigated
using a hypersonic testbed, include aerothermodynamics and flow physics, high-temperature materials, flight controls
and trajectory, instrumentation, and design tools. Captive-carry and air-launch operations are also common areas
between these two classes of vehicles, but the Stratolaunch focus is on the unique challenges associated with
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horizontally mounting and launching a vehicle from an airplane, such as the carrier aircraft. Stratolaunch makes a
distinction in the propulsion area, as its space launch vehicles are powered using liquid-fueled rocket engines, whereas
hypersonic vehicles may utilize air-breathing propulsion, such as scramjets or combined-cycle systems. Non-air-
breathing rocket engines serve as the main propulsion for the hypersonic testbed, while air-breathing hypersonic
propulsion systems or components, to be tested, may be integrated into the vehicle, typically being mounted on the
fuselage lower surface.
B. Hyper-Z Hypersonic Testbed
Prior to the start of the vehicle design process, top-level design requirements and goals were defined in the areas of
operations, propulsion, performance, and payload, as shown in Table 3. Many of these requirements and goals are
derived from the desire for technical linkage between the hypersonic testbed and other Stratolaunch launch vehicles.
Table 3 Hyper-Z top-level design requirements and goals.
Area Design Requirements and Goals
Operations
• Air-launch from Stratolaunch carrier aircraft
• Reusable
• Autonomous
• Horizontal landing on conventional runways
Propulsion
• Liquid oxygen-liquid hydrogen propellants
• Stratolaunch PGA liquid-propellant rocket engine
• COTS propellant system tanks
Performance
• Capable of accelerating to Mach 10
• Accelerator and boost-glide type trajectories
Payload
• Ability to carry external payloads and components
• Internal volume available for payload equipment
From an operations perspective, the vehicle is designed to be air-launched from the Stratolaunch carrier aircraft, fly
autonomously, and return to land horizontally on conventional runways. The Hyper-Z is a reusable vehicle with the
goal of requiring a minimum of post-flight maintenance or refurbishment prior to its next flight. These post-flight
activities may include replenishment of propellants, minor refurbishment of the thermal protection, and normal
inspections and maintenance of systems.
Main propulsion for the Hyper-Z is provided by the Stratolaunch-developed PGA liquid-propellant rocket engine.
Use of the PGA engine in the hypersonic testbed provides validation and risk reduction for flight operation of this new
engine, prior to integration and flight on future Stratolaunch space vehicles. In addition, commercial-of-the-shelf
(COTS) propellant system tanks are used in the hypersonic testbed, rather than requiring the development of unique
tanks, perhaps with complex geometries. Early experience and risk reduction will be gained in the operation of the
associated cryogenic propellant systems, especially for captive-carry and air-launch flight operations.
Performance goals include the capability to accelerate to Mach 10 within the sensible atmosphere. This necessarily
implies flight at high dynamic pressures and high heating rates. Although not stated as an explicit goal, the dynamic
pressure range of interest for hypersonics-related technologies is likely between 1,000 and 2,000 psf [1]. The vehicle
is capable of flying a level acceleration-type profile, reaching a maximum Mach number, maximum temperature
condition, and a boost-glide profile, soaring to an exo-atmospheric, sub-orbital, maximum altitude and performing a
gliding re-entry back into the atmosphere.
In terms of payload-carrying capability, the testbed design is capable of integrating and carrying components,
systems, and other equipment related to hypersonics and space launch vehicle development. As will be discussed in a
later section, the Hyper-Z is configured to mount large, external payloads to its undersurface. The vehicle is also sized
to accommodate the internal carriage of payload-related equipment and systems.
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Figure 7 compares the planned flight envelope of the Hyper-Z with that of space launch vehicles and hypersonic
air-breathing vehicles. As can be seen, the Hyper-Z has the potential to access the flight conditions necessary to
advance the technologies relevant to both of these types of aerospace vehicles.
Fig. 7 Hyper-Z flight envelope compared with hypersonic regions of interest.
1. Vehicle Description
The Hyper-Z is a hypersonic aerospace plane and testbed with a length of 83.4 feet, wingspan of 32.4 feet, and a
nominal launch weight of approximately 65,000 pounds (Fig. 8). The vehicle has a highly swept, thin delta wing and
twin, wingtip-mounted vertical tails. The upper fuselage incorporates the shape of a Sears-Haack-type body, the
theoretically minimum drag, supersonic shape for a given length and volume, while the lower fuselage surface is
essentially flat. A three-view drawing of the Hyper-Z is shown in Fig. 9 and selected specifications are given in Table
3.
Fig. 8 Stratolaunch Hyper-Z hypersonic aerospace plane and testbed.
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Fig. 9 Three-view drawing of the Hyper-Z hypersonic testbed.
Table 4 Selected specifications of the Hyper-Z hypersonic testbed.
Parameter Specification
Length
83 ft 5 in
Wing span
32 ft 5 in
Height
11 ft 4 in
Launch weight
~65,000 lb
Propulsion
1×Stratolaunch PGA rocket engine
Propellants
liquid oxygen + liquid hydrogen
Max Mach in level acceleration
Mach 10+ (at 90,000 feet)
Boost-glide apogee / range
~500,000 ft / ~800 nmi
The main propulsion for the Hyper-Z is the Stratolaunch-developed PGA rocket engine, a throttleable, hydrogen-
oxygen, fuel-rich, staged combustion, liquid rocket engine. The engine is being 100% designed “in-house” by
Stratolaunch and takes advantage of extensive additive manufacturing in its design.
2. Captive-Carry and Air-Launch
The Hyper-Z is designed to be carried aloft by the Stratolaunch carrier aircraft, mounted on a pylon beneath the center
wing section (Fig. 10). Nominal airborne release conditions of an air-launched vehicle from the carrier aircraft are a
Mach number of approximately 0.6 and an altitude of 30 to 35 thousand feet. Depending on the launch vehicle, the
carrier aircraft may have the capability to execute a pull-up maneuver, providing the vehicle with a release flight path
angle of up to 30 degrees.
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Fig. 10 Hyper-Z testbed mounted to carrier aircraft center wing pylon.
The carrier aircraft center wing pylon is shown in Fig. 11. The Hyper-Z is attached to the pylon at several pylon
attach hook points. As shown in the figure, the pylon has substantial volume available for stowage of airborne support
equipment (ASE) for the vehicle. This ASE may include electrical power sources, data acquisition and health
monitoring equipment, fluid systems for propellant system management and purging, and other equipment. Typically,
a forward fairing between the pylon and the vehicle may be installed to reduce aerodynamic drag during captive-carry
flight.
Fig. 11 Carrier aircraft center wing pylon for captive-carry of Hyper-Z.
3. Testbed Payloads
The Hyper-Z vehicle configuration is optimized for hypersonic flight and designed for flexibility in integrating payload
components and geometries that may be of interest to hypersonic and space launch vehicles. For example, the vehicle
undersurface is designed for the integration of large fixtures and components, such as hypersonic flow paths, thin
wing-like surfaces, axisymmetric bodies, or other geometries, as notionally shown in Fig. 12. The Hyper-Z vehicle is
sized with ample volume to accommodate equipment and systems necessary for the flight testing of these technologies.
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Fig. 12 Notional hypersonic payloads.
In addition to the integration of large, complex hypersonic systems on the Hyper-Z, Stratolaunch seeks to develop
a capability where smaller, simpler components and experiments may be carried on the vehicle. This capability may
take the form of multiple “hyper-spots” mounted in various areas of the vehicle, including the flat lower surface,
fuselage or wing upper surfaces, vertical fins, and other areas, as shown in Fig. 13. In this concept, the “hyper-spot”
is a standardized cylindrical container, with the research electronics, systems, etc. placed inside the volume. The
integration of different experiments is simplified by standardizing the interfaces between the experiment and the
vehicle, such as power, instrumentation, fluid systems, etc. A goal of this concept is to make the hypersonic flight
environment accessible to universities, small business, and other smaller concerns.
Fig. 13 Notional “hyper-spot” concept.
4. Vehicle Sub-Systems Packaging
Preliminary engineering work has been performed with the packaging of various vehicle sub-systems and the
calculation of the vehicle mass properties. An example of the packaging of the rocket engine, propellant tanks, and
landing gear is shown in Fig. 14. As mentioned in the previous section, there is significant volume available in the
nose section of the vehicle for the installation of payload equipment and components (shown as the yellow-colored
volumes in Fig. 14). The landing gear arrangement is comprised of a nose landing gear and two main landing gear.
Unlike other retractable landing gear aircraft, the Hyper-Z landing gear need only have an extension function, as the
landing gear are retracted at takeoff and during captive-carry flight on the carrier aircraft.
As shown in Fig. 14, the single PGA rocket engine is mounted to a thrust structure at the aft end of the fuselage.
The main propellant tanks of the current Hyper-Z configuration include a large, cylindrical liquid hydrogen tank in
the center of the fuselage (red-colored cylinder in Fig. 14) and two smaller, cylindrical liquid oxygen tanks on either
side of the hydrogen tank (green-colored cylinders in Fig. 14). Two small, spherical helium tanks, supplying gas for
spin-starting of the rocket engine turbopumps, are located above the rocket engine power pack and one helium tank,
used to pressurize the main propellant tanks, is located forward of the hydrogen tank (helium tanks shown as blue-
colored spheres in Fig. 14).
Details of the Hyper-Z propellant feed system design are in work, as well as the development and validation of the
design tools used to predict the system performance. An example of the propellant feed system design, showing
components and plumbing in the hypersonic testbed vehicle and the carrier aircraft pylon, is shown in Fig. 15.
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Fig. 14 Example of Hyper-Z propulsion and sub-system integration.
Fig. 15 Preliminary propellant feed system design.
Fig. 16 Notional structural layout.
Hypersonic
Vehicle
O2 Topping Tank
Vehicle LOX Tank
H2 Topping Tank
Vehicle LH2 Tank
Pylon
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An initial, notional structural layout of the Hyper-Z is shown in Fig. 16, including the thrust-bearing mounting
structure for the rocket engine. This layout represents an initial structural approach based on conventional, semi-
monocoque aircraft construction. Refinement and optimization of the vehicle structure will be performed during the
design cycle, using results from various analyses, including loads, aero-thermal, and structural dynamics analyses, to
name a few.
5. Aerodynamics and Performance
In the design iteration process to define the vehicle outer mold line, aerodynamic figures of merit include minimum
high-speed drag so as to maximize the final Mach number, high lift-to-drag ratio for increased range, and sufficient
lift in low-speed, higher angle-of-attack flight to obtain acceptable approach and landing speeds. The vehicle
aerodynamics must also result in acceptable longitudinal and lateral-directional stability and control characteristics.
Fig. 17 CFD-derived Mach number contours around Hyper-Z (M=6, H=85,000 ft, α=4°).
Fig. 18 CFD-derived surface pressure coefficient on Hyper-Z (M=6, H=85,000 ft, α=4°).
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During the design process, the vehicle aerodynamics are predicted using computational fluid dynamics (CFD) and
wind tunnel test data. CFD predictions are obtained primarily using three-dimensional, full Navier-Stokes numerical
analyses, using the SolidWorks Flow Simulation [2] and the NASA FUN3D software packages [3]. Example results
from the FUN3D CFD analyses of the Hyper-Z are shown in Figs. 17 and 18. Mach number contours in the flow field
around the vehicle, flying at Mach 6, an altitude of 85,000 feet, and angle-of-attack of 4 degrees, are shown in Fig.
17. The CFD-derived pressure coefficient over the vehicle surface are shown in Fig. 18 at the same flight conditions.
In addition to extensive CFD analyses, wind tunnel tests are being conducted to obtain the Hyper-Z vehicle
aerodynamic characteristics. A low-speed wind tunnel test of the Hyper-Z configuration was recently performed in
the US Naval Academy subsonic closed-circuit wind tunnel in Annapolis, Maryland. Figure 19 shows the Hyper-Z
model mounted in the 42-inch by 60-inch wind tunnel test section. Nominal test conditions were a velocity and unit
Reynolds number of approximately 200 mph and 2 million per foot, respectively. This wind tunnel test provided
aerodynamic and stability data for the Hyper-Z configuration in the gliding, terminal approach and landing phase of
flight. Data from the wind tunnel test is currently being compared with CFD predictions.
Fig. 19 Model of Hyper-Z in US Naval Academy subsonic closed-circuit wind tunnel.
A high-speed wind tunnel test series is planned for the Fall of 2018, commencing with a parametric configuration
test in the NASA Marshall tri-sonic Aerodynamic Research Facility, Huntsville, Alabama. Aerodynamic and stability
data for Mach numbers ranging from approximately 0.3 to 5.0 will be obtained in this test. Additional wind tunnel
tests, including higher Mach number tests, are planned for 2019.
After the aerodynamic database is defined as a function of Mach number, altitude, angle-of-attack, and angle-of-
sideslip, performance predictions are obtained using various trajectory simulations. The Hyper-Z is capable of flying
a wide range of flight profiles to accommodate different vehicle and mission applications. Two example flight profiles
are the maximum Mach number, maximum temperature profile and the maximum altitude, boost-glide profile, shown
in Figs. 20 and 21, respectively.
The maximum Mach number, maximum temperature profile, shown in Fig. 20, begins with vehicle release at 30,000
feet and Mach 0.63, approximately 116 nautical miles off the coast of Southern California. After ignition of the rocket
engine, the vehicle climbs to an altitude of 90,000 feet, where it levels off and continues its acceleration. At engine
cut-off, the vehicle reaches a maximum Mach number of 11.0. This maximum Mach number condition corresponds
to the maximum temperature during the flight profile, which may be of interest for testing hypersonic materials. After
propellant exhaustion, the vehicle decelerates and glides to an autonomous, horizontal landing on the runway at the
Mojave Air & Space Port. For this maximum Mach number flight profile, the vehicle has flown a total distance of
approximately 240 nautical miles with a flight time of approximately 5 minutes.
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Fig. 20 Hyper-Z maximum Mach number, maximum temperature flight profile.
The maximum altitude, boost-glide profile, shown in Fig. 21, starts with release from the carrier aircraft at the same
flight conditions as the maximum Mach number profile, but at an offshore distance of approximately 670 nautical
miles. After rocket engine ignition, the vehicle climbs and accelerates. Engine cut-off is 94 seconds after release with
the vehicle reaching Mach 10.0 at an altitude of 132,000 feet and a flight path angle of 24 degrees. Continuing its
unpowered, coasting ascent, the vehicle apogee is at 477,000 feet and Mach 10.6, approximately 4.3 minutes after
release. After apogee, the vehicle enters a gliding descent, landing at the Mojave Air & Space Port, approximately
11.7 minutes after release, covering a total distance of approximately 790 nautical miles.
Fig. 21 Hyper-Z maximum altitude flight profile.
These two flight profiles represent examples of the types of trajectories and flight conditions that may be obtained
with the Hyper-Z. Other profiles may be tailored to obtain specific flight conditions, e.g. Mach number, altitude,
dynamic pressure, temperature, or other parameters, which may be of interest to particular applications or
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technologies. With its throttleable rocket engine, the vehicle is also capable of maneuvering hypersonic flight, which
may be of interest in simulating a hypersonic target or other types of hypersonic missions.
C. Hyper-A Hypersonic Testbed
As a first step in developing the Hyper-Z hypersonic testbed, Stratolaunch is designing a sub-scale version of the
Hyper-Z, a Mach 6-class hypersonic testbed vehicle, the Hyper-A. As shown in Fig. 22, the Hyper-A has the same
outer mold lines as the Hyper-Z. It also retains many of the design features of the Hyper-Z, including air-launch,
liquid-fueled rocket propulsion, autonomous control, reusability, and horizontal landing. The vehicle has a length of
approximately 28 feet, wingspan of approximately 11 feet, and a launch weight of approximately 6,000 pounds. Table
5 provides selected specifications of the Stratolaunch Hyper-A and compares these with specifications of two other
air-launched hypersonic vehicles, the NASA X-43A and the North American X-15. The sizes of these vehicles are
compared in Figure 23. Note that the Hyper-A is approximately half the size of the North American X-15 and
approximately twice the size of the NASA X-43A. The relative sizes of the carrier aircraft, Hyper-Z, and Hyper-A are
shown in Fig. 24.
Fig. 22 Stratolaunch Hyper-A hypersonic testbed.
Table 5 Selected specifications of the Hyper-Z hypersonic testbed and other hypersonic vehicles.
Parameter
Stratolaunch
Hyper-A
NASA
X-43A
North American
X-15
Length
28 ft 2 in
12 ft 4 in
50 ft 9 in
Wing span
11 ft 4 in
5 ft
22 ft 4 in
Height 3 ft 10 in 2 ft 2 in 13 ft 6 in
Launch weight
6,000 lb
3,000
34,000
Propulsion liquid rocket engine
solid rocket
+ scramjet
liquid rocket engine
Max Mach number
6+
9.6
6.7
Similar to the Hyper-Z, the Hyper-A is also powered by a liquid propellant rocket engine. The propellant tanks are
cylindrical, commercial-off-the-shelf hardware. With a propellant fraction of 60 to 70 percent, design studies indicate
that the Hyper-A may be capable of Mach 6+ flight at dynamic pressures of 1,000 lb/ft2 or greater. In addition, early
design studies and performance analyses indicate that the vehicle may be capable of unassisted takeoff from a
conventional runway, while retaining a supersonic flight envelope.
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Fig. 23 Stratolaunch Hyper-A size comparison.
Fig. 24 Stratolaunch carrier aircraft, Hyper-Z, and Hyper-A hypersonic testbeds.
The smaller Hyper-A hypersonic testbed may be capable of validating many technical areas that are common with
the Hyper-Z, including those related to aerodynamics, stability and control, thermal protection, autonomous flight,
horizontal landing, liquid rocket propulsion, and others. In addition, experience in many operational areas may be
obtained, included those related to payload ground handling, captive-carry flight with cryogenics, airborne support
equipment operations, payload release from the carrier aircraft, and others. It is envisioned that the smaller Hyper-A
hypersonic testbed vehicle may be an economical and efficient way to get to hypersonic flight operations as soon as
possible.
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Figures 25 and 26 show the Hyper-A maximum Mach number flight profiles for an air-launch and a ground,
horizontal takeoff, respectively. The air-launch profile (Fig. 25) is initiated with the carrier aircraft located 63 nautical
miles off the coast of Southern California and 187 nautical miles from the Mojave Air & Space Port. The Hyper-A is
released from the carrier aircraft at an altitude of 30,000 feet, Mach 0.63, and zero flight path angle. After rocket
engine ignition, the vehicle climbs to a level-off altitude of 90,000 feet, reaching Mach 2.6, 107 seconds after release.
Rocket engine cut-off occurs approximately 3.3 minutes after release with the vehicle achieving a maximum Mach
number of 7.7. The vehicle performs a gliding descent to a horizontal landing at the Mojave Air & Space Port,
approximately 6.7 minutes after release from the carrier aircraft.
The ground takeoff flight profile (Fig. 26) begins with a horizontal takeoff from the Mojave Air & Space Port at an
elevation of 2,800 feet. The vehicle initiates a constant Mach 0.8 climb at a flight path angle of 40 degrees. Level-off
is at an altitude of 80,000 feet, approximately 2.3 minutes after takeoff. The vehicle continues to accelerate under full
power, reaching a maximum Mach number of 6.0 at engine cut-off, approximately 3.3 minutes after takeoff. A
climbing turn is initiated for return to the Space Port with the vehicle reaching an apogee of 125,00 feet in the turn.
After completion of the turn, the vehicle is pointed to the Space Port for its final, gliding descent from 75,000 feet,
Mach 2.2 to landing.
Fig. 25 Hyper-A air-launched maximum Mach number flight profile.
Fig. 26 Hyper-A ground takeoff flight profile.
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V. Conclusion
Stratolaunch Systems is pursuing a portfolio of aerospace launch vehicles, which may be air-launched from the
Stratolaunch carrier aircraft. These include reusable space vehicles, capable of reaching low earth orbit, and sub-
orbital, hypersonic vehicles, capable of high Mach number flight within the sensible atmosphere.
Stratolaunch Systems is in the early development stages of a reusable hypersonic testbed, the Hyper-Z, which has
the potential to advance technologies for both hypersonic vehicles and space launch vehicles. The Hyper-Z is a large,
Mach 10-class, reusable, unmanned, autonomously-controlled, rocket-powered hypersonic testbed. The main
propulsion is provided using a Stratolaunch-developed liquid-propellant rocket engine. The vehicle is air-launched
from the Stratolaunch carrier aircraft and lands horizontally on a conventional runway. The Hyper-Z has an external
geometry and significant internal volume conducive to hypersonic flight testing of materials, systems, components,
and other hypersonic technologies of interest. It is capable of flying a wide range of flight profiles, including maximum
Mach number/maximum temperature profiles, boost-glide-type exo-atmospheric trajectories, and maneuvering
hypersonic flight profiles. Various aspects of the Hyper-Z development program have been highlighted in this paper,
including top-level requirements, captive-carry integration, sub-systems packaging, aerodynamics, and performance.
As a first step towards hypersonic flight, Stratolaunch is developing a sub-scale version of the Mach 10-class Hyper-
Z, the Hyper-A Mach 6-class hypersonic testbed. The Hyper-A has the same outer mold line as the Hyper-Z and is
similarly-powered by a liquid propellant rocket engine. This air-launched, horizontal-landing hypersonic vehicle
retains many of the design features and operational aspects of the Hyper-Z. The early flight of the Hyper-A provides
significant risk reduction and operational experience for the development of the Hyper-Z.
Acknowledgements
The authors are grateful for the contributions of the following people in the preparation of this paper; B. Smith, Z.
Swetky, and D. Kaiser with Stratolaunch Systems, D. Miklosovic with the US Naval Academy, D. Gerber, J. Meeker,
J. Steward, and K. Steilow with the National Institute for Aviation Research, G. Burt with Loads and Dynamics Group,
J. Cook with GuideTech, and J. Bowles and L. Huynh with the NASA Ames Research Center.
References
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AFRL-RQ-WP-TM-2013-0260, Wright-Patterson Air Force Base, OH, Nov. 2013.
[2] Dassault Systems SolidWorks Corp., SolidWorks Flow Simulation, Software Package, 2017, Velizy-Villacoublay, France.
[3] Biedron, R.T., Carlson, J., Derlaga, J.M., Gnoffo, P.A., Hammond, D.P., Jones, W.T., Kleb, B., Lee-Rausch, E.M., Nielsen,
E.J., Park, M.A., Rumsey, C.L., Thomas, J.L., and Wood, W.A., “FUN3D Manual: 13.3,” NASA-TM-2018-219808, 2018.
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