Optical scanning system with a crossed scanning pattern

Optical scanning system with a crossed scanning pattern
United States Patent [19]
Harper
[1111
[451 Feb. 19,1974
1541 OPTICAL SCANNING SYSTEM WITH A
3,204,101
8/1965
CROSSED SCANNING PATTERN
3,612,879
3,631,248
10/1971
12/1971
[75] Inventor: Kennard 'W. Harper, Endwell, NY.
[73] Assignee: Ithaco Inc., Ithaca, N.Y.
[22] Filed:
Mar. 17, 1972
[21] Appl. No.: 235,687
[52]
[51]
[58]
US. Cl. ........................ .. 250/83.3 H, 250/83 R
Int. Cl. ............................................ .. G0lj U112
Field of Search .................... .. 250/83 R, 83.3 H
[56]
3,083,611
References Cited
UNITED STATES ~PATENTS
4/1963
Ziolkowski et a1. ..... .. 250/833 H X
3,793,518
Brum?eld et a1.
250/833 H
Ohman .................... .. 250/83.3 H
Johnson ....................... .. 250/833 H
Primary Examiner-Archie R. Borchelt
Attorney, Agent, or Firm-Charles C. Krawczyk
[5 7]
ABSTRACT
An optical scanning system for horizon scanners, and
the like, which provides a dual-lobe crossed scanning
pattern. A detector arrangement receiving radiation
from the scanner provides sufficient signals for deter
mining the attitude of a space vehicle with reference
to a planet about which the space vehicle is orbiting.
28 Claims, 15 Drawing Figures
PATENTEDFEBIQ 1914
‘
sum 1 or 9
SECTION AA
'
3393518
PATENTEDH-IB 1 9 m4
3793518
SHEEI 5 BF 9
LENS (JENTER LINE\\// 50
SCAN PATH *2
'
'
1
3,793,518
2
OPTICAL SCANNING SYSTEM WITH A CROSSED
posite sides of the vehicle having the axes of the conical
scan lying in the roll-yaw plane. The electrical signals
SCANNING PATTERN >
from the scanners corresponding to the crossing of the
earth’s horizon, are translated into pitch and roll error
BACKGROUND OF THE lNVENTlON
This invention pertains to optical scanning systems in
5
general, and more particularly to an optical scanner for
signals for attitude correction. In addition, the electri
cal signals can be processed to provide an indication of
altitude. A scanning arrangement of this type is dis
closed in a U.S. Pat. No. 3,020,407, issued to M.M.
providing a dual-lobe crossed type of scanning pattern
for use with horizon sensors, and the like.
When high ?ying aircraft, such as satellites and space
Merlen and entitled “Horizon Sensor.” Although hori
zon sensors of this type haveebeen successfully used in
the ‘past, such horizon sensors require duplication of
‘craft, orbit a planet such as the earth, at a distance
wherein the planet’s gravity can not be effectively used
to reference the orientation of the aircraft, other
parts resulting in added weight, power consumption
means, such as horizon sensors are required to provide
and multiplication of moving parts, thereby effecting
attitude reference information. The reference informa
the overall statistical life expectancy of the vehicle.
A single scanning arrangement has been developed in
tion is used to maintain the vehicle at a constant atti
tude relative to the planet and therefore reduce any
the prior art that includes two prisms rotated in oppo-_
wobble or attitude error to an acceptable level. The ho
' site directions at a predetermined speed ratio. A scan
rizon sensors provide information, preferably in the
form of electrical signals, that correspond to the depar
ning arrangement of this type is disclosed in a U.S. Pat.
No. 3,083,61 l, issued to Adrian J. Ziolkowski et al and
ture of the vehicle from a predetermined attitude. Atti 20 entitled “Multi-Lobe Scan Horizon Sensor.” The coun
tude correction control systems, such as those employ
ter-rotating prisms produce a multi-lobe crossed scan
ing torque wheels, gas jets, plasma jets, and the like, re
ning pattern having at least ‘three lobes. With this ar
spond to the electrical signals to maintain the vehicle
rangement, the number of lobes to be used in the scan
at a constant attitude. Such attitude correction control
ning pattern is determined by the speed of the scan rel
systems should be adaptable to both high and low or 25 ative to the response of the detection devices, the desir
bits, synchronous orbits, and also highly elliptical or
ability for an even number of lobes, the width of the
bits, without optical or mechanical modi?cations.
lobes, etc. In the particular embodiment disclosed, a
The attitude of a satellite is determined by its position
four lobe scanning pattern was preferred.
with respect to three axes of rotation (or three angular
Although, this multi-lobe scanning arrangement did
degrees of freedom) located at right angles to each 30 eliminate some of the problems of duplication of parts,
other. Two of the axes (pitch and roll) lie in a plane
the arrangement still requires two moving optical ele
normal to a projected radius‘ of the earth passing
ments, large bearings, and corresponding geardrive
through the satellite and the third axis (yaw) coincides
units. In addition, the arrangement also requires, pref~
with such radius. The roll axis (in the direction of vehi
erably, at least a four lobe scan resulting in the detec
cle motion) and the pitch axis (in a direction normal to 35 tion of eight horizon crossings further resulting in
vehicle motion) lie ,in a plane parallel to the planet’s
added complications in signal processing. Furthermore,
horizon. The information pertaining to the roll and
pitch axes can be used to control yaw. For example,
with an attitude control system that applies correction
if it is desired to reduce the width of the lobes of the
scan pattern, the relative difference between the speeds
at which the prisms are rotated is increased, possibly
resulting in a condition wherein the speed of the scan
will be too fast for the detection devices, or else ‘possi
torques to wheels located in the pitch-yar plane, yaw
control can be accomplished by orbital coupling,
wherein, a yaw error existing at one point of the orbit
bly creating undesirably long time constants in the con- . “
becomes a roll error a quarter of an orbit later and thus
trol system if the scan rates are reduced to stay within
eventually all errors are sensed and corrected. Other
the response time of the detection devices.
45
control systems can use gyroscopes, or observation of
The optical scanners of this type require two sets of
heavenly bodies, to provide yaw orientation.
moving parts, one for each prism. Due‘ to the low'pres
sure experienced by vehiclesorbiting in outer space, it
is desirable to maintain such moving'parts in pressur
ized units to minimize lubrication problems. In any
event, itis highly desirable to minimize the number of
The horizon of a planet represents a line of disconti
nuity between the planet ’s atmosphere and outer space.
The line of demarcation between the earth and outer
space i.e., the earth’s horizon, provides a marked dif
ference in infrared radiation. Outerspace is very cold
and provides very little infrared radiation, while the
moving parts, their mass, and the rate at which the‘
parts move, so that lubrication requirements can be
earth ‘s atmosphere is much warmer and‘ provides a sub
minimized.
stantially greater amount‘ of infrared radiation. Al
It is therefore an object of this invention to provide
55
though the scanning system of the present invention
a new and improved optical scanning system.
will be described herein as an infrared earth horizon
scanner (since this is the most important and practical
?eld of utility at the present), it is to be understood,
It is also'an object of this invention to provide a new
and improved. optical scanner system for horizon sen
sors, and the like, requiring only one movable optical
that other types of radiation can also be employed, de- '
unit.
pending upon the planet to be orbited. Therefore,_re~
lt is a still further object of this invention to'provide
a new improved optical scanning system for horizon
sensors that provides a dual-lobe crossed scanning pat
flected visible light, or ultraviolet radiation, or any
other radiation emitted or'_ re?ected by the planet, can
also be used depending upon conditions. surrounding
the planet being orbited.
The horizon scanners presently inuseinclude a‘pair
tern.
65
'
'
.
Itv is a stillfurther object of this invention to provide
a new and improved optical scanning systemproviding»
of, infrared scanners, each providing a conical type
a dual—lobe crossed scan pattern wherein the width of
scan, wherein each of the scanners are oriented on op
the lobe can be changed’witlh'out increasing-the speed‘ -
3,793,518
3
4
of the scan, or requiring additional lobes in the scan
ning pattern.
axis of rotation, respectively, for a zero degree scan po
'
sition.
It is another object of this invention to provide a new
‘
’
FIGS. 5A and 58 illustrates an optical schematic dia
gram of the scanning system of the invention, as viewed
along the axis of rotation, and as viewed normal to the
axis of rotation, respectively, for a scan position in the
and improved optical scanning system for horizon sen
sors that reduces the weight and power requirements
and reduces the number of moving parts thereby in
creasing the systems reliability.
order of 45 degrees.
'
It is still a further objectvof this invention to provide
FIG. 6 illustrates the dual-lobe crossed scanning pat
a new and improved single scanning system for horizon
tern of the optical scanning system of the invention in
sensors that is adaptible to high and low orbits, syn
a position corresponding to correct vehicle attitude.
chronous orbits, and elliptical orbits without modi?ca
FIG. 7 illustrates a three ?ake detector arrangement
tion.
for use with the optical scanning system of the inven
It is another object of this invention to provide an op
tion, for sun radiation rejection.
tical scanning arrangement for transmitting a beam of
FIG. 8 illustrates the position of the optical scanner
radiation in a dual-lobe crossed scanning pattern that 15 of the invention relative to the roll and pitch axis of the
only requires a single moving optical element.
vehicle and in a position corresponding to a correct at
titude position relative to the earth, designating the di
BRIEF DESCRIPTION OF THE INVENTION
rections of the scan paths and the sequence at which
The scanning system of the invention provides a dual
the three ?ake detectors of FIG. 6 receive radiation sig
lobe crossed type of scanning pattern. When used with 20 nals from the scanner depending upon the particular
path scan in the scan pattern.
a
horizon sensors, radiation is received by the scanning
system from the planet which is being orbited and is di
FIG. 9 illustrates a schematic diagram of a control
rected toward detection means for providing electrical
circuit responsive to signals generated by the three
signals corresponding to the attitude of the space vehi
?ake detector arrangement of FIG. 7 for producing
control signals for controlling the attitude of the space
cle relative to the planet’s horizon. In an alternative
vehicle.
embodiment, radiation from a source, such as a laser,
FIG. 10 illustrates a series of waveforms disclosing
is directed at the scanner system, wherein the scanning
the signals processed by the control circuit of FIG. 9
system projects a radiation beam along the dual-lobe
crossed scanning pattern.
‘
’
with a zero attitude error.
.
30
In accordance with the invention the scanner in
cludes at least one optical element, such as a prism, _
.FIG. 11 illustrates a plot of the electrical waveforms
of the control circuit of FIG. 9 wherein a pitch error is
detected.
having a relfective surface, mounted for rotation on an
FIG. 12 illustrates a plot of the electrical waveforms
axis which is at an angle transverse to the re?ecting sur
face and wherein the center line of the optics of the de 35 of the control circuit of FIG. 9 wherein a roll error is
detected.
tector, or radiation source, is located at an angle trans
verse to the axis of rotation, and usually normal
thereto. In the preferred embodiment, a double dove
prism is used having two right angle prisms positioned
with their ‘ reflecting surfaces ' (hypotenae) abutting
each other.
A further feature of the invention includes the use of
a three flake detector for providing an automatic sun
FIG. 13 illustrates a optical schematic diagram of
laser beam scanner according to a second embodiment
of the invention.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
The horizon sensor of FIG. 1 includes a motor drive
radiation rejection function. One of the three ?akes
unit 10 and an optical scanning unit 12. The drive unit
used with one of the other ?akes during one half the
dual-lobe crossed scanning pattern, and is used with the
other ?ake during the other half of the scanning pat
variable speed momentum wheel powered by a two
phase induction motor (not shown). The motor is of a
functions as a common ?ake. The common ?akeis 45 10 includes a reaction wheel arrangement including a
tern.
Control circuit means is provided, responsive to sig
nals generated by the detector means, for producing
control signals for correcting the attitude of the space
vehicle.
constant torque design, that is, the available torque is
substantially independant of operating speed. The rotor
50 14 is outside the stator (not shown) to maximize mo
mentum. The angular position of the rotor 14 is de
tected by (four) magnetic detectors l6A-l6D
mounted on the base 11 and‘located at 90 degree inter
vals adjacent to the circumference of the reaction
wheel
rotor 14. A permanent magnet 18 is fastened to
BRIEF DESCRIPTION. OF THE FIGURES
55
rotor 14, which in turn induces a reference signal in the
FIG. 1 illustrates a vertical sectional view through a
magnetic detectors 16A-l6D as the magnet passes the
horizon sensor including the optical scanning system of
the invention.
FIG. 2 illustrates a top sectional view of the optical
scanner portion of the horizon sensor of FIG. 1 taken
along the lines A*A.
‘
FIG. 3 illustrates an isometric view of the prism of
FIGS. 1 and 2 with the axis of rotation intersecting the
prism re?ective surfaces.
individual detectors.
The optical scanning unit 12 includes, in the pre
ferred embodiment, a double dove prism 20 suitably
fastened to a shaft 22 by a strap mechanism 21 so that
the prism 20 is rotated by the motor driven unit 10. The
double dove prism 20 consists of two right angle Hart
ing-Dove type prisms 24 and 26, each having a silvered
re?ecting surface 28. The two prisms 24 and 26 are ce
FIGS. 4A and 4B illustrate an optical schematic dia 65 mented together with their re?ecting surfaces 28
gram of the scanning system of the invention, as viewed
(hypotenae) abutting and are secured to the shaft 22 by
along the axis of rotation, and as viewed normal to the
the strap mechanism 21, wherein the double dove
3,793,518
5
.
6
prism 20 takes the shape of a rectangular shaped cube.
It can be assumed that the reference point '1 (de
Two opposite corners 23 and 25 of the cube are cut
tected by magneticsensor 16A) of the scanningipattern
away or beveled to simplify‘the securing thereof by the
strap mechanism 21. As will be shown in a later portion
of the specification, only a portion of the scanning pat
35 corresponds to the zero degree position of the dou
ble dove prism 20 as illustrated in FIGS. 4A and 4B. As
the double dove prism 20 is rotated in the direction as
tern of the double dove prism 20 is employed for hori
zon sensing and therefore the strap mechanism 21 will
designated, the scanning system scans in the direction
of scan path No. 1. When the double dove prism 20 is
not interfere with the scanning operation. In the partic
rotated an angle of 90 degress the reference point 2 is -
ular embodiment of the invention as illustrated in
reached and detected by the magnetic sensor 168. Fur
ther rotation of the prism 20 in the same direction
FIGS. 1 and 2, the double dove prism 20 is mounted for
rotation about an axis 30 that passes through opposite
causes the scan pattern to are back towards the'cross
corners 27 and 29 of the cube and transverse a plane
including the re?ecting surfaces 28. In the embodiment
illustrated in FIGS. 1, 2 and 3, the plane including the
reflecting surfaces 28 is displaced relative to the axis of
rotation 30 so that an angle A on the order of 45 de
grees is formed between the axis 30 and a line 31 nor
mal to the plane. Hence, as the prism 20 is rotated
about the axis 30, the re?ecting surfaces 28 provides a
wobbling motion relative to the axis. ,
over point 36 along scan path No. 2. When the double
dove prism 20 is rotated an angle of 180 degrees, the
crossover point 36 is reached a second time and the ref
15
erence point 3 is detected by the magnetic detector
16C. As the double dove prism 20 is further rotated,
the scanning pattern continues to follow in the same di
rection along the scan path No. 2. When the rotation
angle of 270 degrees is reached, the reference point 4
mated radiation and transmits the same to a focusing
is detected by the magnetic sensor 16D. Still further r0
tation causes the scanning pattern to curve back
towards the crossover point 36 along the scan path No.
lens 32. The focusing lens 32, in turn, focuses the beam
1. When a full 360 degree rotation angle is reached, the
The double dove prism 20 receives parallel or colli
of radiation upon a detector 34, illustrated in this par
reference point 1 is detected a second time by the mag
ticular embodiment as ‘a hyper-immersed hemisphere 25 netic sensor 16A. Therefore, it can be seen that a com
bolometer. The axis 37 of the lens 32 intersects the
plete rotation of the double dove prism 20 about the
double dove prism 20 'in the center of the plane 28
rotational axis 30 produces the dual-lobe crossed scan
(.prism hypotenuse) and also intersects, and is normal
ning pattern 35 having a linear or substantially linear
to, the axis of rotation 30. Hence, as the double dove
prism 20 is rotated about the axis 30, each of the re
portion designated by the solid dark lines. This nearly
?ecting surfaces 28 of the prisms 24 and 26 face in the
general direction of the lens 32 during opposite 180 de
gree portions of the rotation of the shaft 22.
The double dove prism 20, as it is rotated, provides
linear portion is used for horizon sensing. Since only a
portion of the scanning pattern is used, the “X” shaped
cut away 42 in the metallic shell 40 (FIG. 1) need only
be large enough to expose the selected crossed portion
a dual-lobe crossed, or “?gure eight,” type scanning
of the scan pattern. In addition, the strapping mecha
nism 21 does not block the linear portion of the scan
pattern 35 as illustrated in FIG. 6. It is to be under
ning pattern.
stood, that the scanning pattern 35, as illustrated in
FIG. 6, shows a general representation of the dual-lobe
crossed shape pattern and is not a scale representation.
de?ne an angle A between the line 31 normal to the
With the plane of the re?ecting surfaces 28 tilted to
be used for sensing of the earth’s horizon 37. The por
plane and the axis of rotation 30, set at 45 degrees (as
illustrated in the particular embodiment of FIGS. 1, 2
and 3) the angle 2A between the scan path No. l and
No. 2 is 90 degrees and scanning paths No. 1 and No.
2 cross at right angles. It should be noted that the shape
tion of the scanning unit 12 (FIG. 1) facing the earth
of the scanning pattern 35 can be changed by merely
provides a radiation transmitting path for the linear
portion of the scanning pattern.
times (as designated by points U, V, W and X) for each
The portion of the scanning pattern 35 near the cross
over point 36 illustrated by the solid lines designates a
linear or nearly linear postion of the scan trace that can
is covered with a radiation transmitting dome 38. Since 45_ changing the angle A. For example, if a narrower lobe
only the portion of the scanning pattern near the cross
pattern is desired, the angle A need merely be in
over 36 is used for horizon sensing, the dome 38 can be
creased. On the other hand, if the lobe pattern is to be
covered with a metallic shell 40 having an “X” type
increased, the angle A is decreased. The wider lobe
cut-away 42 and thereby provide added supporting
pattern may be desirable for low altitude satellites.
strength to the dome 38. The “X” type cut-away 42
The scan pattern 35 crosses the earth’s horizon four
rotation of the double dove prism 20. In response to the
FIGS. 4A and 4B illustrate the position of the double
scanning pattern, the amplitude of the output signals
dove prism 20 in a zero degree rotational position
generated by the detector 34 switched between two
55
which corresponds to the crossover point 36. The radi
levels, that is, a low level signal while scanning outer
ation received from the crossover point 36 is transmit
space and a much higher level signal while scanning the
ted along the centerline 37 of the lens 32 to the detec
earth’s atmosphere. The occurance and duration of sig
tor 34 (as illustrated by the dashed lines). The rotation
nal pulses generated by the detector 34 as the scan pat
of the prism 20 about the axis 30 produces a scan cov 60 tern traverses the earth during scan path No. 1 (be
erage at twice the shaft rotation. This is illustrated in
tween points X and U) and generated during scan path
FIGS. 5A and 58, wherein the prism 20 is rotated to an
No. 2(between points V and W), when compared with
angle of A degrees relative to the center line 37 to pro
the detection of the reference points 1-4 by the mag
duce a scan angle of 2A degrees. Since the rotation of
netic sensors l6A-16D, provides an indication of the
the double dove prism 20 produces twice the scan an 65 attitude of the vehicle relative to the earth’s horizon.
gle, a single rotation of the double dove prism 20
FIG. 7 illustrates a three ?ake infrared detector ar
around the axis 30 produces the dual-lobe crossed
scanning pattern 35 of FIG. 6.
rangement including the flakes 1, 2 and C. The flake C
is mounted within the bolometer with its midpoint posi
3,793,518
7
8
tioned on a first or vertical center line 50 of the bolom
(reference point 2). In a similar manner the ?ip-?op
121 is “set” at the 180 degree rotational angle (refer
eter 34 and at a midpoint between the ?akes l and 2.
The ?akes 1 and 2 are located with their centers lo
ence_poin_t__3_)__g_a_ngi Hisfreset” at the 2-70 dwee rota
tional angle (reference point 3).
cated on a second or horizontal center line 52 of the
bolometer 34. The lines 53 and 54 scribed between the
center point of the ?ake C and the center points of
?ake 1 and 2 de?ne an angle 90 degrees there-between,
and an angle of 45 degrees between the lines 53 and 54
and the center line 50. The combination of the three
?ake detector arrangement along with the control sys
tem of P16. 9 provides for sun radiation rejection. The
detector arrangement is such, taht at least two ?akes
are required to be simultaneously irradiated at any one
time if the signals from the ?akes are to be accepted.
The ?ake C is irradiated simultaneously with either
The output signals from the threshold detector 104
are applied to one input circuit of an AND gate 124,
while the other input circuit is connected to the output
circuit T3 of the ?ip-?op 120. The AND gate 124 is
only enabled during the portion of the scan between
the rotational angle of 90 degrees (reference point 2)
and 270 degrees (reference point 4). Output signals
from the threshold detector circuit 106 are applied to
15
?ake 1 or with ?ake 2. This arrangement is illustrated
by the portion of the scanning pattern illustrated in
one input of an AND gate 126, while the other input
circuit is connected to the inverter 122. The AND gate
126 is enabled only during the portion of the scan be~
tween the rotation angle of 270 degrees (reference
point 4) and 90 degrees ‘(reference point 2).
FIG. 8. As the scanning pattern approached the cross
Output signals from the AND gate 124 are applied
over point 36 scan along path No. 1, the ?ake C and
through an inverter circuit 128 to an input circuit of the
?ake 1 simultaneously receive radiation from the 20 AND gates 130 and 132. In a similar manner output
earth’s horizon. When the double dove prism is rotated
signals from the AND gate 126 are applied through in
an additional 180 degrees to follow scan path No. 2, the
verter 134 to an input circuit of the AND gates 136 and
image of the earth transmitted to the detector 34 is re
138. A second input circuit of each of the AND gates
versed so that the ?akes C and 2 simultaneously receive
130-138 is connected to the output circuit of the ?ake
radiation from the earth’s horizon. in the case of radia 25 C threshold detector 108. Hence the AND gates
tion from the sun, the optical arrangement provides
130-138 can not be enabled unless the detector 74
that only one ?ake will be irradiated at any one time
(?ake C) is irradiated, thereby rejecting signals from
and therefore any signals generated by any one of the
the threshold circuits 104 and 106 and providing sun
?akes C, and 1 or 2, is electrically rejected by the con
rejection. The third output circuit of the AND gate 130
trol circuit of FIG. 9 in a manner as hereinafter ex 30 is connected to the output T1 of the ?ip-?op 118, while
plained.
1
the third input circuit to the gate 132 is connected to
Electrical signals generated by the ?akes 1, 2 and C
T1 output circuit. in a similar manner, the third input
of the AND gate 136is connected to _t_he T2 output cir
are converted by the control system of FIG. 9 into sig
nals corresponding to pitch and roll errors. Each of the
cuit of the ?ip-?op 121, while the T2 output is con
detector circuits 70, 72 and 74 corresponding to ?akes 35 nected to an input circuit of the AND gate 138.
1, 2 and C respectively, are biased for proper operation
The output circuit of the AND gate 130 is connected
by the bias circuits 80-84, respectively. The output sig
through the differential amplifiers 140 and 142 to the
nals from the detectors 70, 72 and 74 are initially pro—
reference clamp circuits 144 and 146 to produce the
cessed by three sets of identical circuitry, each includ
signals Hll(+) and ‘H1l(—). In a similar manner, the
ing a preamplifier (86-90), a DC restorer (92-96), a
output circuit of the AND gate 132 is connected
low pass ?lter (98-102) and a threshold detector cir
through the differential ampli?er circuits 148 and 150
cuit (104-108).
.
to the reference clamp circuits 152 and 154 to produce
The signals from the magnetic detectors 16A-16D
the output signals H21(+) and H21(—). The output cir
are applied to separate ones of the zero crossover de
tector circuits 110-116, respectively. The arrangement
45
is such, that at a rotational angle of the prism 20 of zero
degrees, a signal pulse is applied to the cross-over de
tector 110, at a rotational angle of 90 degrees a signal
pulse is applied to the crossover detector circuit 112,
at a rotational angle of l80 degrees a signal pulse is ap
plied to the cross-over detector 114, and at the rota
tional angle of 270 degrees a signal pulse is applied to
the crossover detector circuit 116. The output circuit
cuit of the AND gate 136 is connected through the dif
ferential ampli?ers 156 and 158 to the reference clamp
circuits 160 and 162 to produce signals H12(+) and
Hl2(—), while the output circuit of the AND gate 138
is connected through the differential amplifiers 164
and 166 to the reference clamp circuits 168 and 170 to
produce the output H22(+) and H22(—). The symbol
(+) indicates that a positive signal of a preset amplitude
is generated, while the symbol (-—) indicates that a neg~
ative signal of preset amplitude is generated. The out
of the zero crossover detector 110 is connected to the
put signals H11(+), H21(-—), H12(+) and H22(—) are
“set” terminal of a ?ip-?op 118, the output circuit of 55 combined to produce a signal S1. The output signals
the zero crossover detector 112 is connected to the
H11(+), H21(—), H12(—) and H22(+) are combined
to produce an output signal S2. The signal S1 is applied
“set” terminal of the ?ip-?op 120, the output circuit of
the zero crossover detector circuit 116 is connected to
the “reset” terminal of the ?ip-?op 120, and the output
circuit of the zero crossover detector 114 is connected
to the “set” terminal of the ?ip-?op 121. The T3 out
put circuit from the flip-?op 120 is connected to the
“reset” input of the ?ip-?op 118 and also through an
inverter circuit 122 to the “reset” terminal of the ?ip
?op 120. Hence, it can be seen that the ?ip-?op 118 is
“set” at the zero degree rotational angle (reference
point 1) and is reset at a 90 degree rotational angle
through a filter circuit 180 and a lead-lag network 182
60
to produce the pitch error signals. The signal S2 is ap
plied through a ?lter circuit 184 and the lead-lag net
work 186 to produce the roll error signals.
The operation of the control system of FIG. 9 will
now be explained with reference to the electrical wave
forms of FIGS. 10-12. It is to be understood, that the
waveforms are not drawn to scale but are exagerated,
since the primary purpose of FIGS. 10-12 is to aid in
the explanation of the timing sequence of reference
9
3,793,518
pulses 1-4 relative to the occurrance of the horizon
sensing pulses from the detectors and the correspond
ing enabling of the gating circuit to produce the various
pitch and roll error signals. The electrical waveforms
are designated with reference letters along the left hand
side of the Figures, which provide a cross reference to
corresponding signals from the circuits of FIG. 9.
As previously mentioned, the timing for the control
system is provided by the reference pulses 1-4 induced
in the magnetic sensors 16A-l6D as the double dove
prism 20 is rotated. The occurance of the reference
pulses (REF1~REF4) are denoted by a sinsusoidal
pulse with a zero amplitude crossover that produces the
timing pulse. The waveforms are referenced to the tim
ing pulses by the verticle lines designated at the top by
REFl-REF4 and at the bottom by the angle of rota
10
stantially shorter in duration than the signals Hl2(+),
Hl2(—), H22(+) and H22(-). When the H signals are
combined, the S2 signal averages out to produce a zero
roll error. However the S1 signal, when averaged out,
produces a negative going error indicating the magni
tude and the direction of the pitch error.
FIG. 12 illustrates the waveforms for the control sys
tem of FIG. 9 in the case of a roll error and zero pi_t_ch
error_. As in the case of pitch error, the signals T1, T1,
T2, T2, T3 and T3 and EC'control the timing of the
AND gates 124, 126, 130, 132, 136 and 138 so‘that dif
ferent durations of H signals are generated. In the case
of roll error, the signals Hll(+), Hl1(—), H22(+),
H22(—) are substantially shorter than the signals
H12(+), H12(—), H2l(+), and H2l(—). When the H
signals are combined, the S1 signal averages to zero in
tion.
dicating a zero pitch error. When the S2 signal is aver
FIG. 10 illustrates the electrical waveforms for a
aged out, a negative going error signal is produced indi
proper attitude of the space vehicle relative to the
cating the magnitude and the direction of the roll error.
earth, i.e. zero roll error and zero pitch error. During 20 Hence, it can be seen that the control system of FIG.
scan path No. l flakes 1 and C cross the earth’s horizon
9 is responsive to the signal pulses generated by the
simultaneously to produce the signals R1 and RC.
Shortly thereafter, the ?ake 2 crosses the earth’s hori
zon to produce the signal R2. During the subsequent
?akes l, 2 and C and the reference pulses REFl-REF4
to produce signals S1 and S2 indicating the magnitude
and direction of any pitch, or roll error, or both. As
scan path No. 2, the ?akes 2 and C cross the earth ’s ho 25 previously mentioned, the ?ake C must be irradicated
rizon simultaneously, while ?ake l crosses shortly
with either of the ?akes l or 2 before the control circuit
thereafter. Hence the signals R1, R2 and RC occurring
during the period including the reference point REFl
(0°), are scan path No. l signals while the signals oc
curring during reference point REF3 (180°) are scan
path NO.‘2 signals. The signals R1, R2 and RC are fil
tered by the filter circuits 98, 100 and 102, respec
of FIG. 9 will process the signals to produce the roll and
pitch errors. This is because the AND gates 130, 132,
136, and 138 can only be enabled by the presence of
the signal EC from the threshold detector 108. In the
event that radiation is received by either of the ?akes
1 or 2, or both, without ?ake _C, such as in the case of
radiation from the sun, the signal EC will not be gener
tively, to remove any noise and produce the signals F1,
F2 and FC. The signals F1, F2 and FC are processed by
ated and therefore none of these AND gates will be en
the threshold detectors 104-108, respectively, to pro 35 abled and no 51 and S2 signals will be applied to the
duce signals El, E2 and EC. The enabling sequence of
lead-lag networks 182 and 186.
,
AND gates 124, 126, 130, 132, 136 and 138 is under
FIG. 13 discloses another embodiment of the inven
the control of the output signals from the ?ip-?ops 1 18,
tion for directing a beam of radiation along the'dual
I20 and 121, as designated by the signals T1, T2 and
lobe crossed-scanning pattern of FIG. 6. A beam of ra
T3, respectively. The AND gate 124 is enabled by the
signal T3 to pass the signal E1 to produce the signal
Elg. The AND gate 126 is enabled by the signal T3
(the opposite of signal T3) to pass the signal E2 to pro
duce a signal E2g. The signals Hll(+) and H11(—) are
generated in the response to the simultaneous presence
diation from a laser source 190 is directed by a tele
scope including lenses 192'and 193 along an axis 194
to the double dove prism 20. The axis 194 intersects
the axis of rotation 30 and is generally normal thereto.
As the double dove prism 20 is rotated, the beam of ra
diation is de?ected in a manner so that the beam fol
of signals T1, Elg and EC. The signals H21 (+) and
lows the dual-lobe crossed scanning pattern.
Although the optical scanning system of the inven
presence of the signals Tl , Elg and EC. The signals
tion has been described in the preferred embodiment
Hl2(——) are generated in response to the simultaneous
including a double dove prism arrangement, it is to be
presence of the signals T2, E2g and EC. The signals 50 understood that the scanning system will also function
H22(+) and H22(-—)'are generated in response to the
with a single dove prism. Such an arrangement canv be
simultaneous presence of the signals T2 , E2g and EC.
exempli?ed by deleting the prism 26 from the scanner
With zero attitude error, the timing of these signals is
in FIGS. 1—-3, 4A, 4B and 5A and 5B, and by keeping
such that the durations of the signals designated by the
the prism 24 intact. In such a case, as the shaft 22 is ro
letter H are essentially equal, and when they’ are com
tated, the single prism 24 will provide the dual-lobe
bined, the signals average out to produce zero pitch
crossed scanning pattern illustrated in FIGS. 6 and 8.
error S1, and zero roll error S2.
The ray diagrams of FIGS. 4A, 48, 5A and 58 will also
FIG. 11 illustrates the waveforms of the signals of the
apply to the single prism arrangement. The advantage
H2l(—) are generated in response to the simultaneous
control system of FIG. 9 when a pitch error is present. 60 of the double dove prism arrangement is that full apera
The relation between the signals El, E2 and EC from
the ?akes l, 2 and 3, along with the timing reference
pulses REFl-REF4, set the ?ip-?ops 118-121 so that
ture is provided for the linear portion of the scanning
pattern providing maximum sensitivity. On the other
hand, the use of the single prism arrangement will .pro
the signals T1, T1, T2, T2, T3, T3 and EC control the
enabling of the AND gates 124, 126, 130, 132, 136 and
duced sensitivity.
138 in such a manner that the H signals are of unequal
duration. Note that in the case of pitch error, the sig
nals H'1l(+), Hl1(—), H12(+) and H12(—-) are sub
vide essentially the same scanning pattern, but at a re
A further modi?cation is the use of a thin double
sided re?ecting mirror, instead of the prisms 24 and 26.
By double sided re?ecting mirror we mean a mirror
11
3,793,518
12
that has a silvered re?ective surface on both sides.
a source of radiation, and
Under this arrangement, the shaft 20 will be suitably
scanning means for receiving radiation from said
connected to the ends of the mirror so that the axis of
source and transmitting the radiation in a dual-lobe
rotation 30 intersects the plane of the mirror at trans
crossed scanning pattern.
verse angle, in a manner as illustrated by the planar sur
-
5. An optical scanning system as de?ned in claim 4
wherein said scanning means includes:
face 28 of HO. 3. in this case, the outline of the prisms
24 and 26 of FIG. 3 can be ignored and the double sides
at least one prism, and
means for rotating said prism relative to said source
mirror is represented by the planar surface 28. Under
such an arrangement, as the shaft 20 is rotated, the mir~
ror will provide the same wobbling movement, relative
to the axis of rotation 30, as the planar surface 28. The
detector 34 will again be mounted relative to the axis
of rotation 30 and the mirror, as it is with the double
so that said prism projects the radiation along said
dual-lobe crossed scanning pattern‘. '
6. An optical scanning system as de?ned in claim 4
wherein said scanning means includes:
a double dove prism, and
dove prism re?ecting surface 28, to receive radiation
7
means for rotating said prism relative to said source
so that said double dove prism projects the radia
re?ected from the mirror surfaces. For an angle of rota~ 15
tion of the shaft 22 of 180 degrees one side of the mir
tion along the dual-lobe crossed scanning pattern.
ror will face the detector 34, while for the other 180 de
7. A horizon sensor for controlling the attitude of a
grees of radiation the other side will face the detector.
space vehicle relative to a space object comprising:
The double side re?ecting mirror will provide a similar
detection means responsive to radiation for produc
dual-lobe crossed scanning pattern as illustrated in
ing an electrical signal;
’
FIG. 6, however having a discontinuity near the zero
scanning means having a dual-lobe crossed scanning
degree and 180 degree etc. points (REFl and REF3)
pattern for scanning the object and transmitting ra
and at a lower effeciency than with the single or double
diation received from object scanned via at least a
dove prism arrangement. The discontinuity at high alti
tude orbits will present problems, however for low alti 25
tude orbits, the discontinuity will be small relative to
the duration of a scan pass across the earth (as it is in
the center of the earth) and can be ignored.
The optical scanning system of the invention has the
advantage of having only one moving unit thereby re
ducing lubrication problems and improving the statisti
30
cal life of the system. In addition, the weight of the
scanner is reduced as compared to the systems of the
prior art thereby reducing problems associated with
portion of the scanning pattern to said detection
means;
signal generating means coupled to said scanning
means for providing electrical signals for identify‘
ing the portions of the scanning pattern being tra
versed, and
circuit means responsive to the electrical signals from
the detection means and said signal generation
means for providing control signals for orienting
the attitude of the vehicle relative to the object.
8. A horizon sensor as defined in claim 7 wherein said
placing satellites into orbit. The shape of the lobes in 3
the scanning pattern can be changed by changing the
scanning means includes:
angle A between the axis of rotation 30 and the re?ect
means for rotating said prism relative to said detec
tion means so that said prism produces the dual
lobe crossed pattern.
9. A horizon sensor as de?ned in claim 7 wherein said
scanning means includes:
a double dove prism, and
means for rotating said double dove prism relative to
ing surface 28. Only one crossed scan across the earth
is required to provide suf?cient information for con
trolling the attitude of the vehicle relative to the earth,
and sufficient information to provide altitude informa
tion. Since only the portion of the scan pattern near the
crossover is used, a cover with an “X” shaped transpar
ent pattern can be provided, thereby minimizing the
45
problems concerned with structural strength.
i claim:
said detection means so that said double dove
prism produces the dual-lobe crossed scanning pat
tern.
1. An optical scanning system comprising:
10. A photoelectric scanning system comprising:
detection means responsive to radiation for produc
?rst optical means including a planar surface having
ing an electrical signal;
two radiation re?ective sides;
means for mounting said ?rst optical means for rota
optical means for imaging radiation on said detection
means, and
scanning means having a dual-lobe crossed scanning
pattern for transmitting the radiation received via
the scanning pattern to said optical means.
2. An optical scanning system comprising:
detection means responsive to radiation for produc
ing an electrical signal;
at least one prism; and
means for rotating said prism relative to said detect
ing means so that said prism produces a dual-lobe
crossing type of scanning pattern and transmits ra
diation to said detection means received with said
scanning pattern.
at least one prism, and
=
3. An optical scanner system as de?ned in claim 2 in
cluding:
two prisms mounted to form a double dove prism.
4. An optical scanning system comprising:
tion about an axis that is transverse to said planar
surface at an angle other than normal so that said
?rst optical means, when rotated, produces a
55
crossed scanning pattern;
radiation sensitive detection means, and
second optical means mounted to alternately receive
radiation from opposite re?ective sides of said ?rst
optical means as said ?rst optical means is rotated
for directing the radiation so received to said de
tection means.
11. A photoelectric scanning-system as de?ned in
claim 10 wherein:
said ?rst optical means includes at least one prism.
12. A photoelectric scanning system as de?ned in
claim 10 wherein:
said ?rst optical means includes two prisms having a
surface of each abutting to form the planar surface.
3,793,518
14
13. A photoelectric scanning system as defined in
claim 10 wherein:
the optical axis of said second optical means lies at
signal in response to radiation applied thereto;
a double dove prism;
an angle substantially normal to the axis of rota
tion.
14. A photoelectric scanning system as de?ned in
claim 13 wherein:
said planar surface forms an angle between 30° to 60°
with the rotational axis.
15. A photoelectric scanning system as defined in 0
claim 10 wherein:
said detection means includes three radiation sensi
tive surfaces for providing electrical signals in re—
sponse to radiation applied thereto.
of the vehicle relative to the space object.
optical means providing a planar surface having tow
radiation re?ective sides;
22. A horizon sensor as de?ned in claim 21 wherein:
said planet is the earth;
.
said radiation sensitive means includes a three ?ake
means for mounting said optical means for rotation
about an axis that is transverse the planar surface
at an angle other than normal so that said optical
means, when rotated about said axis, produces a
infrared bolometer, and
the arrangement being such that the three ?ake bo
lometer, said prism and said optical means provides
corssed scanning pattern;
a means for sun radiation rejection.
means for rotating said optical means about said axis,
and
means for directing a beam of radiation toward said 25
optical means along a direction lying in a plane that
is transverse said axis of rotation to alternately im
pinge on opposite reflective sides of said planar
surface when said optical means is rotated.
17. An optical scanning system as defined in claim 16 30
‘
said optical means includes at least one prism.
23. A horizon sensoras de?ned in claim 21 wherein
said control circuit means includes:
detection means for detecting the rotational position
of the double dove prism, and
circuit means synchronized by said detection means
for converting the signals from the radiation sensi
tive means into signals providing an indication of
the magnitude and direction of any pitch and roll
error.
-
1
.
t
24. A horizon sensor as de?ned in claim 23 wherein:
18. An optical scanning system‘ as defined in claim 16
wherein:
said optical means includes two prisms having a sur 35
face of each abutting to form the planar surface.
19. An optical scanning system as defined in claim 16
wherein:
said beam of radiation is directed along a plane that
is normal to said axis of rotation.
so received to said radiation sensitive means, and
control means connected to receive electrical signals
from said radiation sensitive means for providing
signals corresponding to the pitch and roll attitude
16. An optical scanning system comprising:
wherein:
mounting means for mounting said double dove
prism with one surface of each of the prisms abut
ting, and for rotation about an axis extending at an
angle transverse said abutting surfaces so that said
double dove prism when rotated provides a dual
lobe crossed scanning pattern;
optical means positioned to receive radiation from
the double dove prism and directing the radiation
said circuit means provides signal pulses having a du
ration and a polarity that is a function of the pitch
and roll errors.
25. An optical scanning system comprising:
radiation detection means;
optical means including a surface that is radiation re
40
flecting on opposite sides thereof; and
means for rotating said optical means so that said op
20. A horizon sensing system for space vehicles
adapted for controlling the attitude thereof relative to
space objects comprising:
radiation sensitive means for producing electrical sig
nals in response to radiation applied thereto; opti 45
cal scanning means having a dual-lobe crossed
scanning pattern for directing radiation received
tical means produces a crossed scanning pattern
having a single crossover for each complete rota
tion thereof and directs radiation received via said
scanning pattern onto said radiation detection
means.
26. An optical scanning system as de?ned in claim 25
from said scanning pattern as said object is scanned
wherein:
7
said optical means includes at least one prism.
to said radiation sensitive means, and
control circuit means receiving said electrical signals 50
27. An optical scanning system as de?ned in claim 25
wherein:
from said radiation sensitive means for generating
control signals that are a function of the attitude of
said optical means include two prisms having a sur
said optical means relative to said object.
face of each abutting to de?ne said planar surface.
21. A horizon sensor for providing signals for con
28. An optical scanning system as de?ned in claim 25
trolling the attitude of a vehicle relative to a space ob 55 wherein:
ject comprising:
said optical means includes a double dove prism.
*
*
*
*
*
radiation sensitive means for generating an electrical
65
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement