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AS ULTRALIGHT WAVERIDER VEHICLES |
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A CONCEPTUAL STUDY
BY
GORDON J. ROSS
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AS ULTRALIGHT WAVERIDER VEHICLES |
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A CONCEPTUAL STUDY
BY
GORDON J. ROSS
Waverider Should you wish to contact the
society or require general information please contact ASTRA
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Page please
email: NB - Green numbers within brackets
refer to references. Since the early eighties, interest in
the family of vehicles known as Waveriders has grown
dramatically . Research conducted by universities,
government agencies and amateur groups, has clarified areas
of Waverider dynamics which had previously hindered
development of the concept . In particular, the drag
characteristics of the Waverider have now been established ,
and research into the nature of hypersonic flow at Mach 20
is under way . Much of the new knowledge has been
gained through the use of Computational Fluid Dynamics (CFD)
. Using complex flow modelling programmes, it is now
possible to design a Waverider by changing the geometric
shape of the shockwave. (1)
These optimised designs possess a far
greater degree of subtlety than any Waverider which predates
the use of CFD . The sudden realisation of the Waverider's
potential has accelerated the rate of development in the
field of hypersonic research . The first orbital test of a
Waverider payload may be only two or three years away, as
non-civilian Waverider programmes proceed with new vigour.
(2)
Civilian programmes will undoubtedly follow
close behind, but unlike the defence researchers, civilian
investigators have opportunities to design Waveriders for
many applications. One of the applications currently
under study , is Aero-Gravity Assist (AGA). This technique
entails utilising both the gravitational field of a planet,
and its atmosphere, to effect major spatial course changes
during interplanetary space flight. The concept is not a
novel one, but the use of Waveriders for this purpose is
new, and could significantly affect the range and costs of
planetary exploration and development. With their high lift
and low drag, Waveriders would permit large deflection
angles, and in some cases, vector reversals, for vehicles on
interplanetary trajectories. It is partly for this reason that the
Jet Propulsion Laboratory is looking at Waverider as a
possible delivery system for their Solar Probe mission.
(3)
JPL is looking at the megasonic speed range, where
velocities exceed Earth orbital speed, with planetary
encounter speed of around Mach=100. The JPL Solar Probe
mission requires a very high speed, high G manoeuvre in the
atmospheres of both Venus and Mars, redirecting the orbital
velocity of the Earth which the probe shared at launch and
effectively cancelling it so that probe "falls" into a long
elliptical orbit, whose perihelion lies within four solar
radii, where it will measure the near-solar
environment. The design of Waverider vehicles for
such a demanding mission poses many practical problems. The
exact shape of a Mach=100 shockwave has to be determined, as
well as the chemical interaction of gases encountering the
shockwave at that velocity. It is fairly obvious that the
Waverider for Mach=100 will have to be very slender indeed,
and given the size and the mass of the Solar Probe payload
(3)
, this would require a very long vehicle, possibly too long
to be flown in the Space Shuttle. This problem of size could
make the entire vehicle impractical to build and perhaps
impossible to launch. Another problem area is attitude
control. In its circuit, with the planet acting as a turning
point, the spacecraft is in a forced orbit, flying upside
down with aerodynamic lift directed towards the planet. The
lift vector has to be reversed suddenly and with great
precision in order to leave the atmosphere on the desired
exit trajectory. In a previous paper (4)
the author outlined a "conical roll" manoeuvre which
inverted the vehicle while keeping the shockwave attached to
the leading edges, and suggested "subtractive" control
surfaces, described below, to bring about the
manoeuvre. The Solar Probe mission has spawned
several types of Waverider AGA vehicles. Positioning of the
payload in the airframe is critical to the stability of the
configuration . (5)
Although it has been suggested that the Waverider be built
as part of the spacecraft solar heat shield, this would
create the necessity for a detachable tail section. The
problems of length to semispan ratio have led to a complete
reappraisal of the concept of using Waveriders as
interplanetary manoeuvring vehicle. The design of a
multi-role Waverider for planetary exploration has long been
an objective of researchers, and as such, the idea has some
merit. The difficulty up till now has been
the seemingly insoluble problem of reducing the physical
bulk of the Waverider to a packageable size. It is in this
area that the solution has been found, from a rather
unlikely source, which might make AGA and other Waverider
applications a reality sooner than one might
imagine. The shape of optimised Waverider is
not dissimilar to some form of low speed flexwing; in
particular, there is a strong resemblance to early Rogallo
delta wings. Both have delta planforms, both have highly
swept wings, and both possess a double concavity in their
lower surfaces. Townend, drawing on work by Penland,Daskin
and Peldman, considered that the structure of a Waverider
wing might be made partly flexible in order to save
weight.(6) Page
Two
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Website Author: Nick Portwin (portwin@easynet.co.uk)
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Date Last Modified: 31 07 1999