Stabilizing apparatus

This invention discloses an apparatus for stabilizing a payload assembly including a payload, a maintaining apparatus for at least temporarily maintaining the payload in an airborne environment, and an elongate connection apparatus, which when extended has a vertical length greatly in excess of the combined vertical lengths of the payload and the maintaining apparatus, whereby angular stabilization is a function of the vertical length of the connection apparatus when extended. A method for stabilizing a payload assembly is also disclosed.

FIELD OF THE INVENTION 
The present invention relates to stabilizing apparatus in general and to 
stabilizing apparatus for airborne reconnaissance devices in particular. 
BACKGROUND OF THE INVENTION 
An early aerial photographic system described in U.S. Pat. No. 894,398, 
photographs the earth during free fall of the camera. The system is 
limited because the sharpness of the exposure depends on the shutter speed 
and no means is provided for stabilizing the camera against environmental 
effects such as wind perturbances. 
U.S. Pat. No. 3,184,846 describes a camera which is stabilized by attaching 
it to a plurality of relatively short lengths of cable which are connected 
to a main suspension cable. This arrangement is inadequate for high 
resolution photography. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide an aerial payload stabilizer which 
may be used, inter alia, for high resolution aerial photography and 
reconnaissance. 
There is thus provided in accordance with a preferred embodiment of the 
present invention a stabilized payload assembly including a payload, 
maintaining apparatus for at least temporarily maintaining the payload in 
an airborne environment, and extensible elongate connection apparatus, 
which when extended has a vertical length greatly in excess of the 
combined vertical lengths of the payload and the maintaining apparatus, 
whereby angular stabilization is a function of the vertical length of the 
connection apparatus when extended. 
Further in accordance with a preferred embodiment of the present invention, 
the payload, the maintaining apparatus and the extensible elongate 
connection apparatus are arranged initially to be in close proximity to 
each other in the airborne environment and to subsequently mutually 
distance themselves vertically as the extensible elongate connection 
apparatus is extended. 
Still further in accordance with a preferred embodiment of the present 
invention, the angular velocity of the payload is an inverse function of 
the vertical length of the extensible elongate connection apparatus when 
extended. 
Additionally in accordance with a preferred embodiment of the present 
invention, the payload comprises a reconnaissance apparatus, apparatus for 
rotating the reconnaissance apparatus about any of two mutually 
perpendicular axes of the reconnaissance apparatus and a controller for 
controlling the rotational position and velocity of the reconnaissance 
apparatus. The controller may comprise a compass and a rotation rate 
gauge. 
There is also provided in accordance with a preferred embodiment of the 
present invention, a method of aerial reconnaissance including the steps 
of parachuting a reconnaissance apparatus, a maintaining apparatus and an 
extensible elongate connection apparatus, all initially arranged to be in 
close proximity to one another, stabilizing the reconnaissance apparatus 
by extending the extensible elongate connection apparatus and distancing 
the connection apparatus vertically from the maintaining apparatus, the 
reconnaissance apparatus being mounted on the connection apparatus, and 
acquiring information with the reconnaissance apparatus. 
Further in accordance with a preferred embodiment of the present invention, 
the method further includes controlling the angular rotation of the 
reconnaissance apparatus about any of at least two mutually perpendicular 
axes of the reconnaissance apparatus. 
Still further in accordance with a preferred embodiment of the present 
invention, the reconnaissance apparatus is a line scanner camera. 
Additionally in accordance with a preferred embodiment of the present 
invention, the reconnaissance apparatus is an area camera. 
Additionally in accordance with a preferred embodiment of the present 
invention, the reconnaissance apparatus is maintained at a specified 
spatial angular sector during reconnaissance. 
Still further in accordance with a preferred embodiment of the invention, 
the maintaining apparatus is a balloon. 
In accordance with another preferred embodiment of the present invention, 
the reconnaissance apparatus is sequentially moved to different specified 
spatial angular sectors during reconnaissance.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Reference is made to FIGS. 1-3 which illustrate a stabilized payload 
assembly 10 which comprises a payload 15, maintaining apparatus 20, 
preferably a parachute, and extensible elongate connection apparatus 25 
which preferably comprises a cable 30 and a lowering spool 35, which is 
disposed at the lower end of cable 30. 
It will be appreciated that the maintaining apparatus 20 may alternatively 
be a balloon or any other device that can at least temporarily maintain 
the payload assembly 10 in an airborne environment. 
Initially upon deployment of stabilized payload assembly 10, as shown in 
FIG. 1, assembly 10 typically uncontrollably oscillates through a spatial 
angle A1 measured between a reference vertical axis 12 and a line 
connecting the center of pressure of the maintaining means and the center 
of gravity of payload 15. The radius of oscillation is designated as R1. 
At a predetermined time, depending upon, for example, altitude, barometric 
conditions and mission requirements, the extensible elongate connection 
apparatus 25 is activated by any suitable means such as mechanical, 
electric or pyrotechnic, either directly or indirectly by remote control. 
Activation of extensible elongate connection apparatus 25 causes cable 30 
to unwind from lowering spool 35, thereby greatly increasing radius R1 to 
R2 as shown in FIG. 2. 
Neglecting vertical motion in the direction of axis 12 and considering only 
motion of the stabilizing payload assembly 10 in one plane, it will be 
appreciated that the motion of the stabilizing payload assembly is 
substantially that of a pendulum. 
Letting 
W1=initial angular oscillation velocity of payload 15; 
W2=angular oscillation velocity of payload 15 after extension of extensible 
elongate connection apparatus; 
R1=initial radius of oscillation of payload 15; 
R2=radius of oscillation after extension; 
it will be apparent that W1*R1 represents the maximum velocity of the 
center of gravity of the payload 15 as it oscillates in its initially 
deployed state as shown in FIG. 1. It will also be apparent that W2*R2 
represents the maximum velocity of the payload 15 as it oscillates in its 
stabilizing state as shown in FIG. 2. 
Conservation of energy dictates that the energy of stabilized payload 
assembly 10 in its initial state of FIG. 1 must equal the energy of 
stabilized payload assembly 10 in its stabilizing state of FIG. 2. 
Neglecting the mass of the maintaining apparatus 20, the mass of the 
extensible elongate connection apparatus 25, and neglecting all other 
external forces such as aerodynamic resistance, conservation of energy 
requires that 
W1*R1=W2*R2 
It is seen that the angular oscillation velocity of the payload changes 
inversely with the radius of oscillation. In a preferred embodiment of the 
present invention, typically R1 is approximately 5 meters and W1 is 
approximately 30 degrees per second. Lowering the payload by typically 
about 50 meters, i.e., multiplying R1 by about 10, results in an angular 
oscillation velocity of the payload of only about 3 degrees per second. 
The angles of oscillation before and after extension, respectively A1 and 
A2, are related to the radii of oscillation substantially as follows: 
EQU (R1/R2)=(sin(A1/2)/sin(A2/2)).sup.2 
Since for angles up to 30 degrees, the angle in radians is approximately 
equal to its sine, (R1/R2) is approximately equal to (A1/A2).sup.2. Thus 
the angle of oscillation decreases as the inverse of the square root of 
the ratio of radii. In the typical example mentioned above, a lowering of 
the payload by 50 meters causes a decrease in the oscillation angle of 
about threefold, typically from about 20 degrees to about 6 degrees. If 
the payload is an aerial camera, the resultant stabilization leads to 
reduced blur commensurate with the reduction of the angular velocity. 
It will also be apparent that any disturbance or perturbation in the motion 
of maintaining apparatus 20 caused by external forces such as a gust of 
wind, will be substantially reduced by the relatively long length of cable 
30. 
It will be appreciated that the analysis of motion of the maintaining 
apparatus 20 and the payload 15 presented hereinabove represents first 
order effects only and that the actual motion is considerably more 
complex. It is believed however that the overall motion of the maintaining 
apparatus 20 and payload 15 is substantially as described by the equations 
shown hereinabove. 
Referring now to FIG. 3, in a preferred embodiment of the present 
invention, the payload 15 preferably comprises a camera 40 which is 
preferably a line scanner camera. The camera is preferably gimballed to 
allow rotation thereof about two mutually perpendicular axes. In the 
embodiment of FIG. 3, rotation is possible azimuthally about yaw axis 41 
and elevationally about axis 42. It is appreciated that a gimbal (not 
shown) may also be constructed which allows further rotation about axis 
43, which is mutually perpendicular to axes 41 and 42. 
In a preferred embodiment of the present invention, rotation is 
accomplished by means of an azimuth motor 51 and an elevation motor 52. 
Typically the motors are servomotors and along with camera 40 are 
controlled by a controller 55. Controller 55 preferably stabilizes the 
camera 40 about axis 41 in a closed loop control system. Controller 55 and 
motors 51 and 52 are preferably powered by a battery 57. The control loop 
preferably comprises a compass 58 and a rotation rate gauge 59. 
Alternatively, the camera 40 may be stabilized by controller 55 using a 
conventional gyroscope, rate gyro, or any other directional or angular 
velocity sensor, in the closed loop. 
For certain reconnaissance requirements, the payload 15 may also comprise 
an antenna 60 and a transmitter 65. Alternatively, the transmitter may be 
substituted by a receiver (not shown) or transceiver (not shown) together 
with a central processing unit (not shown). Antenna 60 may also be 
controlled in a closed control loop in substantially the same manner as 
for camera 40. 
It is appreciated that the stabilized payload assembly 10 suitable for use 
in aerial reconnaissance. The assembly 10 is typically parachuted from any 
type of aircraft such as an airplane or a rocket or is parachuted after 
being launched from any suitable launcher. Extensible elongate connection 
apparatus 25 is then extended to achieve stabilization of payload 15. 
Motors 51 and 52 in conjunction with controller 55 may be used to further 
stabilize the reconnaissance apparatus, such as camera 40 or antenna 60. 
In one typical reconnaissance mission, the reconnaissance apparatus may be 
maintained at a specified spatial angular sector. Alternatively, the 
reconnaissance apparatus may be sequentially moved to different specified 
spatial angular sectors. 
Reference is now made to FIGS. 4-6 which illustrate a stabilized payload 
assembly 110 constructed and operative in accordance with another 
preferred embodiment of the present invention. The embodiment of FIGS. 4-6 
differs from that of FIGS. 1-3 in that the payload 115 preferably 
comprises a lowering spool 116 which is disposed at the top of cable 130. 
The remainder of the payload 115, designated in FIGS. 4 and 5 by reference 
numeral 118, may be identical to that shown in FIG. 3, identical or 
equivalent elements being represented in FIG. 6 by identical reference 
numerals with the addition of the prefix 1. The operation of the apparatus 
of FIGS. 4-6 may be substantially equivalent to that of the apparatus of 
FIGS. 1-3. 
Reference is now made to FIGS. 7-9 which illustrate a stabilized payload 
assembly constructed and operative in accordance with yet another 
preferred embodiment of the present invention. The embodiment of FIGS. 7-9 
differs from that of FIGS. 1-6 in that the extensible elongate connection 
apparatus comprises unusually long connection cables 148 directly 
connected to the parachute canopy 149. No unwinding spool is provided and 
after activation, the free fall of the payload 215 pulls the cables 148 
taut as illustrated in FIG. 8. The payload 215 may be identical to that 
shown in FIG. 6, identical or equivalent elements being represented in 
FIG. 9 by identical reference numerals with the addition of the prefix 2. 
The operation of the apparatus of FIGS. 7-9 may be substantially 
equivalent to that of the apparatus of FIGS. 1-6, once the cables 148 are 
taut. 
Reference is now made to FIGS. 10-12 which illustrate a stabilized payload 
assembly constructed and operative in accordance with still another 
preferred embodiment of the present invention. The embodiment of FIGS. 
10-12 differs from that of FIGS. 7-9 in that the extensible elongate 
connection apparatus comprises a single long connection cable 170 directly 
connected to the conventional cables 162, which are conventionally 
associated with a parachute canopy 164. 
As in the embodiment of FIGS. 7-9, no unwinding spool is provided and after 
activation, the free fall of a payload 166 pulls the cables 170 and 162 
taut as illustrated in FIG. 11. The payload 166 may be identical to that 
shown in FIG. 9, identical or equivalent elements being represented in 
FIG. 12 by identical reference numerals with the addition of the prefix 3. 
The operation of the apparatus of FIGS. 10-12 may be substantially 
equivalent to that of the apparatus of FIGS. 1-9, once the cables 170 and 
162 are taut. 
Reference is now made to FIG. 13 which illustrates one scan pattern 
arrangement which can be achieved using the apparatus of the present 
invention. This pattern can be achieved, for example, by operation of 
elevation motor 52, and then by operation of azimuth motor 51, providing 
mutually opposed rotation of the upper and lower portions of the payload 
about axis 41. It will be apparent that other scan patterns similar to 
that of FIG. 13 may be obtained by operating azimuth motor 51 in different 
steps. Thus, for example, the scan pattern of FIG. 13 is obtained by 
rotating azimuth motor 51 in steps of 60 degrees. 
The scan pattern of FIG. 13 may also be obtained by scanning once with 
elevation motor 52, rotating azimuth motor 51 60 degrees while returning 
the elevation motor 52 to its starting position, scanning again with 
elevation motor 52, rotating azimuth motor 51 by 60 degrees again while 
returning elevation motor 52 to its starting position again, scanning 
again with elevation motor 52 and then rotating azimuth motor 120 degrees 
in the opposite direction and returning the elevation motor 52 to its 
starting position. 
FIG. 14 illustrates another embodiment of a stabilized payload assembly 
415. The payload assembly 415 may be identical to that shown in FIGS. 
1-12, identical or equivalent elements being represented in FIG. 14 by 
identical reference numerals with the addition of the prefix 4. The 
embodiment of FIG. 14 differs from the embodiment of FIG. 3 in that it 
provides rotation of the camera 440 about different gimbal axes 442 and 
443. Elevation motor 422 and motor 420 providing control about the 
respective axes 442 and 443. 
FIG. 15 illustrates one scan pattern arrangement which can be achieved 
using the embodiment shown in FIG. 14. The motor 420 is first operated to 
produce a rectangular shaped scan pattern. The elevation motor 422 is then 
operated to move to a different area whence motor 420 is again operated to 
produce another rectangular shaped scan pattern. 
Reference is now made to FIG. 16 which illustrates another embodiment of a 
stabilized payload assembly 515. The payload assembly 515 may be identical 
to that shown in FIG. 3, identical or equivalent elements being 
represented in FIG. 16 by identical reference numerals with the addition 
of the prefix 5. The apparatus of FIG. 16 differs from that of FIG. 3 in 
that the camera 540 is rotatable only about axis 541. 
FIG. 17 illustrates a scan pattern arrangement which can be achieved using 
the apparatus of FIG. 16. This pattern can be achieved by rotating the 
motor 551 about axis 541 in a sufficient number of substantially equal 
steps to cover the entire field. Typically, 16 or 32 such steps may be 
employed. 
It will be apparent that the scan pattern arrangement of FIG. 17 may also 
be achieved by the apparatus shown in FIGS. 3 by rotating motor 51 about 
axis 41 in substantially equal steps to cover the entire field. 
Reference is now made to FIG. 18 which shows another embodiment of a 
stabilized payload apparatus. The apparatus of FIG. 18 differs from that 
of FIG. 3 in that rotation of the payload about axis 641 is not actively 
stabilized by electronic means. The passive stabilization provided by the 
long length of cable 630 may provide a sufficiently stable platform for an 
array camera 640 to produce satisfactory pictures. It will be appreciated 
that the array camera 640 may be tilted with respect to axis 641 to 
increase the area covered by the array camera 640. It will also be 
apparent that any rotational motion about axis 641 caused by twisting of 
the long cable 630 will increase the area covered by the array camera 640. 
Reference is now made to FIGS. 19-21, which illustrate various mechanisms 
for joining the elongate connection apparatus to a payload. FIG. 19 shows 
a single cable 180 coupled typically via three attachment cables 182, 184 
and 186 to three points on a payload 188, which points are mutually 
azimuthally separated, typically by 120 degrees. 
FIG. 20 illustrates an embodiment similar to that of FIG. 19, wherein 
elongate axial energy absorbers 190 are arranged in series along each of 
typically three attachment cables 192, 194 and 196. 
In both of the foregoing embodiments, the cables may be replaced by rods. 
FIG. 21 illustrates an alternative embodiment of the invention wherein a 
connection cable 200 is coupled to a resilient, energy absorbing elongate 
connector 202, which is fixedly attached to a payload 204. The connector 
202 is configured to reduce movement of the payload relative to the cable 
200, by absorbing energy as it is deformed under load. 
It will be appreciated by persons skilled in the art that the present 
invention is not limited to what has been particularly shown and described 
hereinabove. Rather, the scope of the present invention is defined only by 
the claims that follow: