Field of the Invention
This invention relates to tracking systems for
aiborne missiles, and more particularly, to tracking
devices that have a wider field-of-regard to prior art
devices and yet do not significantly affect the
aerodynamic performance of the missile.
Background of the Invention
Airborne missiles are provided with seeker and
tracker heads for locating and homing on targets. Such
heads comprise a detector or detectors, of any type
known in the art, such as optical or radar detectors; a
scanning mechanism, which actuates the detectors with a
scanning motion; a shield or shields to protect the
detectors from the environment; and electronic
processing means for processing the information received
from the detectors and guiding the missile accordingly.
At each moment and in each position, each detector
has an instantaneous field-of-view, which depends on its
structure, and can be defined as the solid angle that
includes all the directions that are "seen", viz. from
which a signal can reach the detector and be sensed by
it. This will be called hereinafter briefly "the field-of-view".
As the detector is scanned, the field-of-view
changes. The sum of all possible fields-of-view, or, in
other words, the solid angle that includes all the
directions that can be "seen" by the detector in its
scanning, will be called herein "the field-of-regard".
The field-of-regard does not depend only on the
structure of the detector, but depends also on the
scanning mechanism and on the other parts of missile
that may limit the width of the scanning and/or obstruct
in certain positions the detector's field-of-view.
Clearly, the seeker and tracker device is unable to
detect a target that is outside its field-of-regard, and
is unable to keep track of detected targets, if they
move to outside its field-of-regard.
Obviously, a seeker and tracker device placed in
front of the tip of the missile will have a wider field-of-regard,
but it will cause air drag, particularly in
high speed cruising, and damage the aerodynamic
performance of the missile. Further, it will be greatly
exposed to aerodynamic attrition and consequent
overheating.
The prior art has not found any way to provide a
wide field-of-view without creating aerodynamic and/or
thermal drawbacks. Thus, USP 3,974,985 discloses a
tracker comprising a rotatable lens barrel mounted on a
turret mounted in a tubular section of a missile located
aft of the missile tip. Such a tracker causes a limited
air drag, but has a limited field-of-regard.
Israeli patent application discloses a missile
having a homing head arranged in an intermediate
position of the missile, which homing head is at a slant
to the missile axis and views the environment through a
lateral window. Such a device does not damage the
aerodynamic performance of the missile, but has a poor
field-of-regard.
UK patent application GB 2 284 465 A discloses a
seeker head movable between two positions: a first
position in which it extends forwardly of the missile
tip and a second position in which it is retracted aft
of said tip. In the first position it has a wide field-of-regard
and can search for a target, while in the
second position it has a very narrow field-of-regard
which is intended to permit it to track a detected
target. Such a seeker head, however, not only involves a
mechanical complication and serious overheating problems
when in said first position, but is able to track a
detected target, in said second position, only if the
target's movement is not quick or sharply angled. While
said application states that, if an infrared detector is
used, a cooling system may be used for cooling the
interior of the seeker head, no cooling system is shown
or described.
It is therefore a purpose of this invention to
provide a seeker and tracker system for missiles, which
is free of the drawbacks of the prior art.
It is another purpose to provide such a system that
has a wide field-of-regard, and yet has no significant
influence on the aerodynamic performance of the missile.
It is a further purpose to provide such a system
that is capable of tracking a detected target no matter
how it moves.
It is a still further purpose to provide such a
system that is not affected by heat developed from air
attrition.
It is a still further purpose to provide such a
system that does not involve any mechanical
complication.
It is a still further purpose to provide such a
system that achieves concurrently all the objects and
advantages achieved separately by prior art systems, and
further, objects and advantages that are not achieved by
them.
Summary of the Invention
The seeker and tracker device according to the
invention comprises;
I - at least an optical sensing unit (briefly,
hereinafter, "sensing unit"), comprising a lens barrel
or sensor barrel, which preferably has an axis in a
transverse plane of the missile; II - a dome, projecting from the side of the
missile and covering the sensor barrel, said barrel
extending into said dome beyond the side surface of the
missile; III - a detector, preferably coaxial with the
missile; III - drive means for rotating the sensor barrel
about two perpendicular axis; and IV - a processor for processing the signals
produced by the detector and guiding the missile
accordingly.
Of the aforesaid two perpendicular axis, one (that
can be called the "inner" one) is connected to the
sensor barrel while the other (that can be called the
"outer" one) is connected to the first. Said two axes
together constitute a gimbal suspension.
The sensing unit comprises a lens (objective lens)
barrel, extending into the dome beyond the side surface
of the missile and having a field-of-view that depends
on the optical characteristics of its components, first
drive means comprising a first (pitch) motor and an
inner joint for imparting to said barrel a pitching
motion about a first axis, second drive means comprising
a second (roll) motor and an outer joint for imparting
to said barrel a rolling motion about a second axis, and
optical deviating means, generally comprising mirrors or
prisms, for transmitting the optical signals sensed by
the objective lens to the detector, which receives them
through an ocular lens. It should be understood that the
expressions "ocular lens" or "objective lens" include
the case in which one or the other or both of the
"lenses" is an optical sensor comprising more than one
optical component, e.g. more than one lens or a
combination of lenses and other optical components. Such
optical sensors are well known to skilled persons and
need no further description. Therefore the "lens barrel"
will be synonymously called the "sensor barrel".
The rotation of the sensor barrel about its axis
will be called herein "roll" or "rolling motion". By
"pitch" or "pitching motion" is meant herein rotation
about an axis perpendicular to the axis of the sensor
barrel. When no pitching motion has occurred, said axis
is in its average position, viz. it lies on a plane
perpendicular to the missile axis. The pitching swings
it fore and aft of the average position. The combination
of the pitching and the rolling motions generates a
practically hemispherical, or 180°x360°, field-of-regard
for the optical sensor.
The sensing unit is located in an intermediate
portion of the missile. A radar antenna dish or
conformal antenna strips can be housed in the portion of
the missile forward of the sensing unit.
The device of the invention is periscopic and
transmits the picture as it is without additional
mechanical motion. The pitching motion becomes a rolling
motion of the picture. This motion can be computed and
it is possible to neutralize said rolling motion or at
least to take it into account at the time of signal
processing and of calculation of the tracking error.
In a preferred embodiment of the invention, cooling
means are provided for the sensing unit, which comprise
a cooling fluid reservoir, a cowling for directing a
flow of coolant fluid released from the tank to the rear
surface of the dome, and motor and transmission means
for rotating the dome about its axis, whereby every
portion of its surface in turn will come into contact
with the coolant. The cooling fluid may be, for example,
a gas such as nitrogen or argon under a pressure of e.g.
2000 psi, or ethylene glycol under low pressure.
In another preferred embodiment of the invention,
at least two sensing units are provided, angularly
spaced about the periphery of the missile, and
preferably coaxial and on opposite sides of the missile,
whereby it can be said that they are the specular image
one of the other. Optical means, such as an optical
coupler, is also provided, selectively to render one or
the other of the sensing units operative, by directing
to the detector only the optical signals originating
from said operative unit. Shutter means are preferably
provided for preventing optical signals, received by the
sensing unit that is not operative at the moment, from
interfering with the optical signals transmitted by the
operative sensing unit. The optical coupler and the
shutters are controlled by the processor. When a target,
that is being tracked by a sensing unit, moves out of
the field-of-regard of that unit, and therefore the
signals concerning it cease to be transmitted to the
detector and from it to the processor, this latter
deactivates said unit and activates the other unit.
When two sensing units are provided, each has a
field-of-regard that is approximately emispheric, viz.
approaches 180x360°. Therefore, together, the two sensing
units have complementary fields-of-regard which
practically cover the entire space around the missile.
This invention therefore comprises a method of
tracking targets from missiles, which comprises
providing in the missile two optical sensors having
complementary and symmetrical fields-of-regard; tracking
a target by means of an operative optical sensor while
maintaining the other sensor inoperative; and when a
targets moves out of the field-of-regard of said
operative optical sensor, deactivating it and activating
the other optical sensor to continue tracking the
target.
Brief Description of the Drawings
Fig. 1 is a schematic axial cross-section of the
fore portion of a missile having a sensing unit and a
detector mounted thereon; Fig. 2 is a like cross-section at a larger scale
showing two sensing units, a portion of the missile
being broken off; Fig. 3 is a cross-section similar to Fig. 1, but
additionally showing cooling means; Fig. 4 is a view from the outside of the cooling
means; Fig. 5 is a cross-section similar to Fig. 1, but
additionally showing a radar antenna dish; Fig. 6 is a cross-section similar to Fig. 2, but
additionally showing conformed antenna strips.
Detailed Description of Preferred Embodiments
In Fig. 1, the fore portion of a missile is
schematically indicated at 10. Numeral 11 generally
designates a sensing unit, which extends from a outer
surface of the missile and is protected by a dome 14 of
optical material. 12 is a detector axially mounted in
the missile. Sensing unit 11 comprises a sensor barrel
13 which is actuated for pitching motion by a motor 15
and is supported by bearing 16. An outer axis 17 is
provided for permitting a rolling motion, actuated by
rolling motor 20 supported on bearings 21. Sensor barrel
13 has an opening 18 through which the optical signals
pass. They impinge on a succession of mirrors 19 and on
a central mirror 23, placed so as to reflect the optical
signals to detector 12 provided with an ocular lens 22.
Fig. 2 shows a similar missile 10 in which two
sensing units 11 and 11' are mounted opposite to each
other and on the same axis, so that unit 11' is the
specular image of unit 11. Each sensing unit is
identical to sensing unit 11 of Fig. 1, and therefore
its components are the same and need not be described
once more. Detector 12, with ocular lens 22, is equal or
equivalent to detector 12 of Fig. 1. Additionally, an
optical coupler 25 is provided in place of central
mirror 23 of Fig. 1, to reflect the optical signals from
either sensing unit 11 or 11' into the detector.
Shutters 26 and shutter actuators 27 are also provided.
Figs. 3 and 4 illustrate a cooling system for a
single sensing unit, as that of Fig. 1, but it is clear
that the same cooling system can be used for both
sensing units, when two are present as in Fig. 2. The
missile and the sensing unit are indicated by the same
numerals as in Fig. 1. Additionally, a motor 30 and a
gearing 31 are provided for rotating dome 14 on supports
32. A cowling 33 leads a cooling fluid from a reservoir,
not shown, to the dome. The cooling fluid is discharged
as indicated by the arrows 34. Because the dome rotates,
all its surface is successively exposed to the cooling
gas and cooled.
Fig. 5 shows the same apparatus as in Fig. 1, with
the addition of a radar antenna dish 40 mounted on a
pedestal 41.
Fig. 6 shows the same apparatus as in Fig. 1, with
the addition of conformed antenna strips 42. Obviously,
such antennae could be mounted in missiles provided with
two sensing units, as in Fig. 2.
While embodiments of the invention have been
described for purposes of illustration, they are not
limitative and skilled persons may carry out the
invention with many adaptations, modifications and
variations.