Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reissue Patent
1999-05-20
2001-08-14
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S003210, C244S003220
Reissue Patent
active
RE037331
ABSTRACT:
1. FIELD OF THE INVENTION
The invention relates in general to the field of maneuver control of a vehicle traveling through a fluid environment (e.g., air, water, plasma) and more particularly to a maneuver strategy implementing dual-control devices to improve vehicle maneuverability. Specifically, the invention describes a dual-control autopilot that allocates control commands to two control mechanisms (positioned forward and aft of a vehicle's center of gravity) in such a manner as to provide increased dynamic capability.
2. BACKGROUND OF THE INVENTION
An application which exhibits an immediate need for the improved maneuverability provided by this invention is an interceptor missile. Enemy offensive missiles pose an escalated challenge for interceptor missiles.
Modem
Modern
threat configurations are designed to realize reduced radar signatures, make use of expanded countermeasures, travel at extremely high velocities over unpredictable or difficult to predict trajectories, and employ large magnitude lateral evasive maneuvers. In order to accomplish body-to-body impact, the interceptor missile must achieve large transverse acceleration levels in a very short period of time to move the vehicle perpendicular to its flight path to ensure collision.
As shown in
FIG. 1
, a missile system can be described as an elongated body
100
that travels through a fluid medium. The missile
100
has a forward section and an aft section divided by a point of center of gravity
105
. Forward of the center of gravity
105
is a forward control device such as thrusters
110
. The aft section has an aft control device such as fins
115
. It will be apparent to one of ordinary skill in the field that other alternative control devices are possible. For instance, the forward control device could be implemented as canards rather than a thrusters. Similarly, the aft control device could be implemented via thrust-vector controls techniques.
FIG. 1
shows the vehicle configuration, sign convention, and notation used in this discussion for a body fixed coordinate system allowing motion in the x-z plane. Table 1 describes the notation introduced in FIG.
1
.
TABLE 1
Notation
Symbol
Description
x
longitudinal body fixed (righ-hand) Cartesian
coordinate
y
transverse body fixed (right-hand) Cartesian
coordinate
z
Universe body fixed (right-hand) Cartesian
coordinate
N
z
transverse acceleration load factor along body
axis z
q
missile pitch rate about body axis y
U
0
longitudinal velocity along body axis x
w
transverse velocity along body axis z
&dgr;
&bgr;a
aft fin deflection angle
&dgr;
thr
magnitude of applied thrust force
A missile moves in a transverse direction in response to an applied control force according to the laws of physics. Below the altitude of approximately 20 kilometers, a missile's primary source of transverse acceleration is the aerodynamic force resulting from the missile body being at an angle with its velocity vector (angle of attack). Flight control devices (e.g., forward thrusters
110
and/or aft fins
115
) obtain this angle of attack by applying to rotate the missile's front end in the direction of the intended maneuver.
A functional block diagram of a conventional missile control system is shown in FIG.
2
. Block
200
represents the physical vehicle (i.e., the missile) and incorporates all vehicle subsystems including, for example, control actuation, propulsion and inertial measurement systems as well as aerodynamic configuration. The vehicle's measured dynamic response is shown as feedback signal
205
. This signal encodes, for example, a measurement of the missile's
100
rotational and translational rates and accelerations. The missile guidance logic shown in block
210
provides a commanded dynamic response signal
215
which encodes a desired maneuver along a kinematic trajectory. The difference between the desired and measured responses produce the error signal
220
in a conventional feedback architecture. The autopilot controller
225
uses the error signal to generate a control signal
230
. This control signal encodes commands to actuate the vehicle's control devices. For example, the control signal
230
could be degrees of deflection of a fin or canard, or degrees of deflection of a rocket motor nozzle, or percentage of maximum thrust of an attitude control motor, etc.
2.1 Forward Control Device Systems
One type of conventional missile control system employs a forward control device only. An example of this type of missile system is the FLAGE missile designed by LTV Aerospace Corporation (now Loral Vought Systems, the assignee of this application). The FLAGE missile employs active control of forward thrusters to achieve maneuverability. In the FLAGE missile, aft fins are fastened in a fixed canted position to provide stabilization and rolling characteristics.
A conventional control scheme employing a forward control device (e.g., thrusters) only is shown in FIG.
3
. In response to a command signal
300
(corresponding to command signal
215
) from the guidance system
210
for a desired step increase in lateral acceleration in the positive z-direction, the missile's autopilot controller
225
generates a time varying thruster command signal
305
(corresponding to control signal
230
) to effect the maneuver. Actuation of the lateral control thrusters produce the measured acceleration response
310
in the positive z-direction normal to the vehicle's body. It is conventional to illustrate the acceleration by normalizing with the missile's weight producing a load factor N
z
having the units of g-force.
At time t
o
guidance system output (
215
and
300
) commands a step increase in positive z-axis acceleration. Referring to signals
305
and
310
, between times t
o
and t
1
the autopilot controller
225
commands the forward thrusters to deliver a force
305
in the positive z-direction to rotate the missile's nose in the positive z-direction
310
(also known as a negative pitching moment). Between times t
1
and t
2
, the autopilot controller commands the thrusters to deliver a negative force
305
to slow the missile's downward rotation. After time t
2
, the autopilot controller commands a positive force
305
to hold a steady rate and acceleration in the positive z-direction
310
. (Note, one skilled in the art will realize that this description also applies to accelerations in other directions.)
It is important to note that forward control mechanisms achieve missile rotation by applying a force in the direction of the maneuver, that is, ALL missile acceleration
310
is in the direction of the maneuver.
2.2 Aft Control Device Systems
Another conventional missile control technique employs an aft control device only. Examples include the Patriot missile system (Raytheon), VT-1 missile system (Loral Vought Systems) and the ATACMS missile system (Loral Vought Systems). In these systems, active control of the aft flight control surfaces (fins or thrusters) are employed to achieve maneuverability.
A conventional control scheme employing an aft control device (fins) only is shown in FIG.
4
. In response to a command signal
300
(corresponding to command signal
215
) from the guidance control system
210
for a step increase in acceleration in the positive z-direction, the missile's autopilot controller
225
generates a fin control signal
400
(corresponding to the control signal
230
) to effect the maneuver. Signal trace
405
represents the missile's measured transverse acceleration response N
z
from the missile's inertial measurement system (corresponding to the feedback signal
205
), where N
z
is described above with respect to FIG.
3
.
At time t
o
guidance system output (
215
and
300
) commands a step increase in positive z-axis acceleration. Between times t
o
and t
1
the autopilot controller
225
sends a command signal
400
(corresponding to control signal
230
) to actuate the missile's aft fins to deflect in a direction opposite the desired maneuver (sign conven
Chin Gary
Lockheed Martin Corporation
Sadacca Stephen S.
Sidley & Austin
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