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8
The Committee on Hypersonic Tech-
nology for Military Applications was
formed in early 1987 by the Air Force
Studies Board of the National Research
Council in response to a request from
the Air Force Systems Command. We
were asked to evaluate potential appli-
cations of hypersonic air-breathing
vehicles to military missions, and to
assess the status of those technologies
critical to the feasibility of such
vehicles. Further, we were asked to
examine the full range of issues relevant
to potential military hypersonic applic-
ations, including the classes of missions
and the types of vehicles that would be
appropriate to them, at least to the
extent that understanding of such issues
is necessary to an evaluation of hyper-
sonic technologies. We determined very
early in our proceedings that a firm
conceptual basis for military air-
breathing hypersonic operations, that is,
a set of mission scenarios, does not yet
exist. Therefore, our discussion of
potential missions will be relatively
brief; the principal emphasis of our
discussion will be the status of the
critical technologies.
In the time frame of the commit-
tee's activities, the National Aerospace
Plane program has dominated hypersonic
research in the USA. With its focus on
technology development for, and prelim-
inary design of, a research vehicle
capable of air-breathing operation to
orbital speeds without staging, the NASP
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION
INTRODUCTION 1
program has highlighted hypersonic
technology requirements and provided
the bulk of the support for hypersonic
years. The
program has led to a review and to some
extent rediscovery of the rather exten-
sive work done on hypersonic propulsion
and configurations in the 1 960s and
early l970s. It has, therefore, also been
the source of much of the committee's
information on the status of hypersonic
technologies. Our assessment of hyper-
sonic capabilities is thus to some extent
in the context of the tentative require-
ments set for the NASP research vehicle.
However, other requirement statements,
perhaps somewhat less demanding of the
critical hypersonic technologies, may
ultimately be of considerable interest to
the Air Force. We have attempted to
maintain this perspective in our deliber-
ations.
research for the last three
The committee was briefed by all
major government and industrial par-
ticipants in hypersonic research and
technology development, including the
relevant units of the Air Force Wright
Aeronautical Laboratories, the NASP
Joint Program Office, and NASA Langley
Research Center. Individual members of
the committee had additional contacts
during this period. Two members of the
committee were members of the NASP
Review Panel of
Board, providing
the Defense Science
the committee as a
whole with an insight into that group's
findings. After the selection of con
~To assure the widest dissemination, a special effort has been made to publish this
report without security restrictions. The committee believes that it has adequately
examined and reported the state of the technology to provide the reader with an
accurate assessment of hypersonic technology development without divulging classified
information.
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INTRODUCTION
tractors for Phase Il. the preliminary
design phase of the NASP Program, we
were briefed by the two propulsion
contractors selected for phase 2B, and
met informally with the other prospec-
tive propulsion contractor who par-
ticipated in Phase 2A. The committee
was then briefed by the three airframe
contractors selected for phase 2, part 2.
To ensure that we and the several
contractors engaged the issues that the
committee believed were important, we
prepared a questionnaire and sent it to
the contractors through the director of
the NASP Joint Program Office (see
Appendix B). In general, the contractors
responded quite adequately to our quer-
ies, and added their own special points.
Inevitably, many judgmental issues
arise in any assessment such as this.
We have tried to ensure that we under-
stand the views of the hypersonic
research and technology community, and
to the extent that we agree, we have
incorporated these judgments in this
report. But the final responsibility for
the findings and recommendations of this
report rests with us, and where our
views differ from others, our experience
and judgment have prevailed.
In addressing our charge, we have
placed the major emphasis on evaluation
of the technologies most critical for
hypersonic flight. We judge these to be,
in order of importance:
.
9
throughout the flight corridor from
takeoff to orbital or near-orbital
velocity.
We have evaluated these technologies
against our perception of the needs for
military hypersonic flight in the broadest
sense.
the supersonic combustion ramjet
(scramjet) engine
the technology of integrating such
engines with the airframe, including
the aerodynamics and control of the
resulting "flying engines"
the structural concepts and high-
temperature low-density materials
required to achieve the desired
weight fractions
guidance and control of such large,
flexible, complex vehicles as result
from the requirement to operate
Also in keeping with its charge, the
committee has examined the technology
needs for the experimental hypersonic
vehicle, the X-30, which is the focal
point for the NASP program. We believe
the design of the X-30 requires suffi-
cient understanding of the critical tech-
nologies to enable the design of a
reusable vehicle (or vehicles) with
reasonable assurance that they will be
able to fully explore the flight cond-
itions of interest for hypersonic flight
vehicles. Tentatively, this envelope
includes the Mach number range from 0
to 25, at associated altitudes such that
the dynamic pressure is in the range
from 500 to 2000 psf. It includes steady
state flight as well as acceleration and
deceleration in the hypersonic regime.
Since the X-30 will be a research
vehicle, we believe that it may reason-
ably incorporate technologies that are
not fully mature; however, given the
high visibility and cost of the program,
they will have to be sufficiently reliable
in an experimental context to assure
that the program can be completed and
realize its experimental objectives.
These requirements are considerably less
demanding than those for an operational
vehicle with the same envelope, in terms
of the required reliability, durability,
and safety of the vehicle. On the other
hand, they are more demanding of oper-
ational flexibility if the vehicle is to be
capable of accessing all parts of the
altitude-Mach number space that may be
of interest for various possible oper-
ational vehicles, any one of which may
have to operate in a more limited envel-
ope. As will be elaborated in the ensu-
ing discussion, the research vehicle may
require special features, particularly in
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10
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION
propulsion and control, that will not be
required in an operational vehicle.
Facilities for testing can be con-
sidered a critical issue for hypersonics.
Indeed, if the NASP program were to
proceed in the classical way, with full
verification of all major components and
systems before flight, a major national
commitment would be required, far
exceeding that presently planned. We
have not addressed this possibility. We
have taken the view that the NASP pro-
gram must depart from the classical
approach by making much more extensive
use of numerical modeling (made possible
by recent advances in computational
fluid dynamics), and by depending more
on flight research. There is no other
option, if the NASP program is to pro-
ceed on the planned schedule.
It is not clear that full validation
testing is possible at the high Mach
number limits of the envelope, but even
if feasibility could be established, 10 or
more years would be required to design,
build, and activate such major facilities.
In connection with the NASP program,
we have therefore asked how existing
facilities can best be used, and what
component testing is feasible on the
time scale of the NASP program.
In the context of long term oper-
ational uses of hypersonic vehicles, the
issue of test facilities must be reexam-
ined. If we are to build such vehicles,
extensive testing capabilities probably
will be needed to ensure their econom-
ical development. This committee has
not addressed this issue in depth.
Representative terms from entire chapter:
hypersonic technology
