U.S. patent number 3,807,658 [Application Number 05/300,558] was granted by the patent office on 1974-04-30 for rate transmittal method for beamrider missile guidance.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Jimmy R. Duke, Walter E. Miller, Jr., Robert L. Sitton.
United States Patent |
3,807,658 |
Miller, Jr. , et
al. |
April 30, 1974 |
RATE TRANSMITTAL METHOD FOR BEAMRIDER MISSILE GUIDANCE
Abstract
In beamrider guidance of a missile toward a target, tracking or
error detination is accomplished on board the missile. Rate
information obtained at the launch site must be transmitted to the
missile if it is to be used in the guidance thereof. Rate
information allows correction of the inherent lag of a missile
behind the target line-of-sight. A method of electronically
accomplishing the equivalent of an optical boresight shift allows
the missile direction to be adjusted to compensate for the inherent
lag of the missile as it moves toward the target.
Inventors: |
Miller, Jr.; Walter E.
(Huntsville, AL), Duke; Jimmy R. (Huntsville, AL),
Sitton; Robert L. (Huntsville, AL) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
23159602 |
Appl.
No.: |
05/300,558 |
Filed: |
October 20, 1972 |
Current U.S.
Class: |
244/3.13 |
Current CPC
Class: |
F41G
7/26 (20130101) |
Current International
Class: |
F41G
7/20 (20060101); F41G 7/26 (20060101); F41g
007/14 (); F42b 015/02 (); F42b 015/10 () |
Field of
Search: |
;244/3.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Webb; Thomas H.
Attorney, Agent or Firm: Kelly; Edward J. Berl; Herbert
Voight; Jack W.
Claims
We claim:
1. In a beamrider missile guidance system wherein a target is
tracked by visual line-of-sight from a tracking station and the
missile is directed toward said target substantially along the
line-of-sight axis, a method of transmitting rate information
within the beam path and comprising the steps of:
directing optical energy from said target tracking station along
the line-of-sight to the target,
spatially encoding said optical energy for providing a plurality of
individually modulated optical frequency beams,
forming said individually modulated beams into a single beam of
adjoining segments, and
modifying at least one of said beam segments by alternately
modulating the beam segment with the modulation rate of an
adjoining segment.
2. In a beamrider missile guidance system a method of transmitting
rate information within the beam path as set forth in claim 1 and
further comprising the steps of:
forming said beam segments into a quadrant,
nutating said beam for sequentially sweeping a portion of
respective quadrants across the missile directed toward said
target, and
alternately modulating said modified beam segment with a portion of
said adjoining segment signal modulation which portion is equal in
magnitude to missile lag.
3. In a beamrider missile guidance system a method of transmitting
rate information within the beam path as set forth in claim 2 and
further comprising the step of: detecting by said missile the
duration of respective quadrant modulation rates during nutation
for the further step of controlling the error correction of the
missile trajectory toward said target.
Description
BACKGROUND OF THE INVENTION
Beamrider guidance is a method of guidance whereby a missile is
enabled to determine its own relative position in a transmitted
beam, due to spatial encoding of that beam. The missile generates
guidance commands to correct missile flight path toward the center
of the transmitted beam. A gunner then points the beam at a target,
and the missile follows the beam to target impact. Since the
missile generates its correctional commands internally there is no
requirement for correctional or tracking guidance from an external
source.
However, the line-of-sight rate resulting from a moving target or a
moving transmitter causes a missile guidance error. This guidance
error is defined as "lag" of the missile behind the changing
line-of-sight of the transmitted beam. Since this changing
line-of-sight may be measured at the transmitter as an angular
rate, it can be used to reduce the missile guidance error caused by
line-of-sight rate. Since guidance commands are generated on board
the missile, any rate information must either be transmitted
directly to the missile, or be used to alter the boresight of the
transmitter to compensate for predicted missile lag. Rate
transmission requires either a separate transmission link or a
multiplexing method. Mechanical or optical boresight shift
mechanisms are not capable of providing the .+-.0.1 milliradian
accuracy required.
A beamrider missile guidance method and apparatus are disclosed in
patent application Ser. No. 275,014, filed July 25, 1972 by Miller
et al. Miller et al. disclose an improved beamrider missile
guidance system wherein an observer at a launch site visually
locates a target. A line-of-sight to the target is established
through a telescopic sight. An optical transmitter, boresighted to
the telescope, directs optical energy toward the target.
Transmitted optical energy is spatially encoded to allow on board
missile sensors to respond to missile deviation from the observer's
line-of-sight to the target. Error information generated in the
missile allows automatic missile correctional commands for
returning the missile to the line-of-sight.
SUMMARY OF THE INVENTION
In a beamrider missile guidance system a moving target is tracked
by visual line-of-sight from the target tracking station or launch
site. The missile is launched substantially along the line-of-sight
axis to the target. Rate transmission for beamrider guidance is
encoded into the existing guidance information with the same code
or frequencies already present in the beam. The transmitted beam,
formed of individually modulated beam segments, has one or more
segments modified by alternately modulating the segment with the
modulation rate of an adjoining segment. This alternate modulation
of adjoining segments provides electronic adjustment of the optical
boresight so that the beam null is leading the target by an amount
equivalent to the inherent missile lag, the missile trajectory is
effectively corrected to place the missile directly on target.
Thus, missile trajectory is corrected at the tracking station
without transmitting any additional signals in the beam.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an embodiment of the beamrider guidance system.
FIG. 2 is a static cross-section of a four-quadrant beam having
four codes or frequencies for respective quadrants.
FIG. 3 is a diagram of the signal resulting on the missile for
on-axis conditions without rate encoding.
FIG. 4 is a signal diagram resulting on the missile for on-axis
conditions with rate encoding included.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, FIG. 1 discloses an optical
beamrider system. A target tracking station 10 directs an optical
beam from a source 12 toward a target 14. Source 12 is boresighted
to follow telescopic tracking of the target by an observer or
gunner at the tracking station. A missile 16 is launched into the
path of beam 18 toward the target. An optical receiver 19 on the
missile's aft end responds to the spatially encoded light beam 18
for directing the missile toward the center of the beam. The beam
center is the line-of-sight axis 20 between target tracking station
10 and target 14.
FIG. 2 discloses the cross-sectional beam pattern of a static beam.
Separate beams I, II, III and IV are brought together in quadrants
to form the single beam 18. These beam segments are coded to
distinguish respective quadrants. The four-quadrant beam is nutated
in space with a nutation radius equal to approximately one-half the
beam radius. The missile detector 19 then sees, sequentially, the
four codes (frequencies) of the four quadrants, with a duty factor
that is dependent on missile location within the beam. This duty
factor provides measurement of missile position error in the
beam.
Typical of ideal conditions a missile is shown in dotted lines
centered on axis for the four-quadrant beam of FIG. 2. As the beam
is nutated, the missile will sequentially receive the codes of
quadrant I, II, III and IV with equal duration of each quadrant (as
also shown in FIG. 3). If, however, the missile is displaced to the
right of the center the relative duration of codes I and IV will be
increased and the durations of codes II and III will be decreased.
The missile error signal is determined from these relative
durations. However crossing motion by the target or tracker results
in a consistently displaced missile which is continuously seeking
alignment. Missile displacement to the right as shown in FIG. 2 is
caused by a right to left crossing target and the resulting
line-of-sight rate. Correction of this lag with lead adjustment is
accomplished by a shift of the boresight to the left. The boresight
shift is equal to the expected missile lag as determined by the
angular line-of-sight rate measured at the beam transmitter.
FIG. 3 shows the signal resulting on the missile for the on-axis
condition. Left to right missile position in the beam is given by
the relative duration of the quadrants on the missile sensor 19.
Thus, (I and IV) - (II = III) provides the yaw signal where
positive is right error and negative is left error in the figure.
If these durations are equal, the average yaw error is zero.
Referring now to FIG. 4, the signal in quadrant II is modified to
be an alternating code frequency f.sub.1 (code I) for a short time,
and code II or frequency f.sub.2 for a short time. This produces,
for an on-axis missile, the yaw signal of FIG. 4. A positive or
right error has been indicated, since the average yaw signal is
positive. Thus, the boresight axis has shifted. By making the
boresight axis shift approximately equal to the error caused by the
line-of-sight rate, correction for this error is accomplished.
Missile electronics respond to the signals received by detector 19,
sensing the relative time duration of respective pulses and
combining these signals to activate correctional guidance. Thus the
missile is directed to lead a target by the equivalent amount of
lag caused by the line-of-sight rate, thereby placing the missile
directly on axis with the actual target. Reversal of the
intermodulation, f.sub.2 into quadrant I, would be used for lead in
the opposite direction.
Quadrants III and IV can also be used for boresight shifting, in
order to make the shift in yaw independent of missile pitch errors.
Codes I, II, III and IV may easily comprise separate frequencies
f.sub.1, f.sub.2, f.sub.3, and f.sub.4, allowing simplified
detection of time duration signals.
Although a particular embodiment and form of this invention has
been illustrated, it is readily apparent that various modifications
and embodiments of the invention may be made by those skilled in
the art without departing from the scope and spirit of the
foregoing disclosure. For example, since all four quadrants can be
intermodulated, other biases can be corrected for. Thus, a gravity
bias can be programmed to provide missile lift as a function of
expected missile velocity (time), and wind velocity can be measured
and corrected for if desired. Accordingly, the scope of the
invention should be limited only by the claims appended hereto.
* * * * *