ENGINEERING ANALYSIS CAMERA SYSTEM, AERIAL RECONNAISSANCE HIGH ACUITY, 18 X 18 INCH FORMAT, TYPE HR-244

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP67B00511R000100150007-8
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 10
• Document Creation Date: December 9, 2016
• Document Release Date: December 15, 1999
• Sequence Number: 7
• Publication Date: January 5, 1961
• Content Type: STUDY

Approved For Releo 2001/03/30: CIA-RDP67B005WO00100150007-8
ENGINEERING ANALYSIS
CAMERA SYSTEM, AERIAL RECONNAISSANCE
HIGH ACUITY, 18 x 18 INCH FORMAT, TYPE HR-244
This study was done to consider the available hardware components and
techniques compatible with the requirements for a photographic reconnaissance
system capable of obtaining small ground resolution (on the order of 1 foot)
from altitudes between 80, 000 and 120, 000 feet at air speeds of Mach 0. 9 to
3. 0. The system is to be capable of providing "spot" coverage over a number of
specific targets or to provide total coverage over a large area.
The study was to consider the current state-of-the-art in photographic
systems in terms of the performance capabilities of the hardware components as
they now exist and for the time period of two years. Particular attention was
devoted to the possibilities inherent in the existing basic HR-248 Camera for
upgrading, through the use of an improved high-acuity lens.
Attached is a specification and an outline drawing describing the proposed
camera system resulting from this study. Following is a brief synopsis of the
significant engineering analysis and computations performed in developing the
specifications.
Velocity:
80, 000 feet,
120, 000 feet,
80, 000 feet,
120, 000 feet,
Mach 0. 9s
Mach 0. 9x
Mach 3. 0=
Mach 3. Oa
Rg (ground recognition):
0 (angular resolution):
Film:
Weight:
Volume :
80, 000 to 120, 000 feet
Mach 0. 9 to Mach 3. 0
872 ft/sec
940 ft/sec
2910 ft/sec
3135 ft/sec
1 foot on the ground over target area
8. 35 x 10- 6 radians (minimum)
Thin-base, high resolution
600 pounds, maximum
Limited
2. LENS AND FOCAL LENGTH CONSIDERATIONS
Lens-film combination resolutions necessary to obtain a one-foot ground
recognition at low contrast are listed below for lenses of several different focal
lengths.,
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Lens focal length 24" 36" 48" 60" 72"
Required resolution (1/mm) 197 131 98 80 66
The largest lens focal length that can be accomodated in the available volume
is 48 inches. To achieve a lens-film resolution of 100 lines per millimeter with
a 48-inch focal length lens will require the use of high-resolution film, either
SO-243, SO-213, or SO-130.
The two basic types of cameras considered for the 244 application were
panoramic and framing. To use a panoramic camera and still attain the required
transverse angular coverage, a short focal-length (24 inch or less) would be
required. Because of the shape of the volume available. a longer focal-length
(48 inch) folded-lens framing camera capable of wide transverse angular coverage
can be more readily fit into the volume available. The tabulation below lists the
angular coverage for different configurations and various focal lengths of panoramic
and framing cameras:
Total Transverse Angular Coverage
24" F. L.
36" F. L.
48" F. L.
Split Panoramic
1200
1040
-
Framing
230?
175?
140?
The following tabulation lists the ground coverage available and assumes the
use of a 9-inch wide format for the panoramic camera and an 18 x 18 inch format
for the framing camera:
Altitude
80, 000 feet
120, 000 feet
Split Panoramic (24"f. l.)
45 n. m.
68-1/2 n. m.
Framing (24" f. 1.)
70 n. m.
105 n. m.
Because of the larger transverse angular-coverage capability, and the
lower system resolution necessary to attain the required one-foot ground resolu-
tion, the 48-inch focal length folded-lens framing camera is recommended.
5. CAMERA CHARACTERISTICS
5. 1 Cycle Rate. To attain the transverse angular coverage of 1400, the
camera must take a vertical photograph and three oblique photographs on each
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side of vertical, and do so in sufficient time to provide a minimum of 55 per cent
forward overlap of all frames. The camera cycling sequence is indicated in the
following diagram:
Required cycle rates for the seven-position mode at the two altitude extremes
and two velocity extremes are tabulated below:
Altitude
Mach 0. 9
Mach 3. 0
80, 000 feet
3. 00 sec
0. 87 sec
120, 000 feet
4.45 sec
1. 30 sec
Other combinations of oblique positions and modes of operation are available;
however, cycle rates of these other modes will be longer than those shown in the
preceding table.
5. 2 IMC Rates. Image motion compensation rates over the range of
altitudes and velocities will vary from 7.8 milliradians per second to 36.4
milliradians per second. IMC rate accuracy required to maintain the one-foot
ground resolution figure will vary with shutter speed and IMC rate. Required
IMC rate accuracies for various conditions of camera operation are listed below:
Shutter Speed, per sec 1/50 1/50 1/100 1/100
IMC Rate, per milliradian/sec 36 25 18 7.8
Required IMC Rate Accuracy 1. 2% 1. 6% 2. 3% 5. 3%
5. 3 Types of IMC. Movement of the photographic image with respect to
the film emulsion must be reduced to an acceptable limit during the exposure.
Image motions are produced by vehicle forward velocity, vehicle stabilization
errors, and vibration. Proper image motion compensation can be calculated
for image motion produced by the vehicle forward velocity, with the accuracy
determined by type of image motion compensation applied, accuracy of known
parameters, degree of stabilization, and limits of vibration.
Required Cycle Rate, Seconds/Cycle
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Image motion compensation is achieved by one of two means, the first of
which is the effective movement of the film in the focal plane and, second, the
effective rocking of the focal plane and optics. Several methods for achieving
the above compensation are presently used in modern aerial cameras. Effec-
tive moving film compensation can be attained by actual translation of the film
in the line-of-flight or by a lateral displacement of the lens in the line-of-flight.
An effective rocking motion can be attained by actual rocking of the entire camera
system, or by rotation of a viewing mirror. In rocking motion compensation,
additional effects can be attained, dependent on the axis of rotation. The most
desirable axis is a horizontal axis, parallel to the ground plane and perpendicular
to the line-of-flight. The following discussion is based on the rocking-mirror
IMC about an axis transverse to the line-of-flight and parallel to the ground plane.
5. 3. 1 Proposed IMC (Rocking Mirror). In the discussion of rocking
film compensation, the first assumption will be based on the ideal system analysis
ignoring stabilization, vibration, and accuracy of known parameters. These
factors will be discussed in a later paragraph. A complete analysis has been made
of the IMC by rotation about a transverse axis through the principal point on the
optical axis. It can be shown that the error in the "X" in-flight direction is:
dx s *X2
H2
where: dx = movement of a point in the "X" direction.
The negative sign indicates that point
moves in an opposite direction to the
line-of-flight.
X a distance of the transverse axis in feet
v s velocity in feet/seconds
C z shutter speed in seconds
H : altitude in feet
The error in the "Y" transverse direction can be shown to be:
dy x xy
where: dy a movement of a point in the "Y" transverse
direction. A negative sign indicates a point
aft that moves towards the line-of-flight,
and a positive sign indicates a point forward
that moves from the line-of-flight.
The resultant motion of an image is the vector sum of the movements in the
"X" and "Y" directions.
G
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where: Y R = resultant movement in feet
v a velocity in feet per second
t = shutter speed in seconds
H = altitude in feet
X = distance of point from transverse axis in feet
Y = distance of point from in-flight axis in feet
Figure 1 represents a plot of the ground resolution capability as a function
of field of view. The resolution figure is based on movement of one bar width as
defined by MIL-STD-150. The shaded area shown in each position format
represents the area within a 100 line per millimeter capability. The velocity is
assumed as 3, 220 feet per second (Mach 3. 0), altitude as 120, 000 feet, and
shutter speed as 1/250 second.
This shows that the vertical picture is compensated over the entire format
for a 100 line per millimeter system with focal length of 48 inches and a format
size of 18 x 18 inches. With 55 per cent overlap, a three-position mode provides
full coverage within 100 lines per millimeter of total field of view. A seven-
position mode provides almost full coverage within 100 lines per millimeter
except for a small area in the far-oblique. Calculations show that this area has
a better than 70-line-per millimeter resolution.
5. 4 Stabilization. To maintain a one-foot ground resolution, the camera
will require a stabilized platform from which to operate. The stabilizer will have
to be sufficient to maintain the stabilized pitch and roll rates to a value less than
t 0. 3 milliradians per second.
The H-244 Stabilized Mount will steady the camera adequately to enable the
operating photographic system to resolve an angle of 8 microradians at shutter
speeds as low as 1/60 second. The mount will consist of a 3-axis flexure
knuckle gimbal, three torquing motors, and vertical and one rate gyro (principal
sensors). The electronic package will employ solid-state components in printed-
board type construction.
The flexure knuckle will permit t 30 of freedom about each axis. This
component was selected for high degree of reliability necessary in an inaccessible
location, light weight, and for negligible maintenance requirements. No other
type of mount has even been proven, under operating conditions, to fulfill the
critical requirement for stability.
The remainder of the mount complement employs conventional design and
will vary only in detail.
5. 5 Shut er. To realize high light transmission efficiency and reliable
operation, a two-curtain, focal plane shutter will be utilized.
A between-the-lens shutter was considered and subsequently rejected. The
large lens aperture would require large shutter blades. At the higher shutter
speeds, blade velocities would become quite high, as would the forces required
to start and stop the shutter blades; consequently, a shutter of this type would
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create considerable shock and vibration.
For this application, a focal plane shutter was felt to be a less complex, more
reliable, and inherently a more versatile device. A wide range of shutter speed is
available by varying either slit width or curtain speed. Because relatively slow
curtain speeds may be used, shock and vibration forces will be smaller in
magnitude and more readily subject to control and/or isolation.
For the proposed HR-244 focal plane shutter, it is anticipated that a broad
range of shutter speeds, I. e. , for winter as opposed to summer operation, will
be set by means of a manual shutter slit-width adjustment prior to the mission.
Variations within the broad range may be selected in flight and are achieved by
changing curtain velocity. Figure 2 shows the shutter speed range for a typical
winter mission. For a constant slit width of 0. 8 inches (dashed vertical line),
three different curtain speeds will provide effective shutter speeds of 1/60 second,
1/125 second, and 1/250 second.
Because the shutter curtain can be placed close to the focal plane, the light
transmission efficiency of a focal plane shutter is inherently higher than that of
a between-the-lens shutter. Shutter efficiency will vary with both effective
shutter speed (slit width) and curtain distance from the focal plane. Figure 3
shows the variation in efficiency with shutter speed with the shutter curtain placed
at two different distances from the focal plane.
5. 6 Environment. The high resolution, 48-inch lens will have a very shallow
depth of focus, in the order of f 0. 002 inch. Therefore, to maintain focus, the
camera environment must be closely controlled. Environmental temperature
variations cannot exceed f 4o F. and pressure variations must be held to less than
* 4 mmHg. Figure 4 shows the allowable temperature and pressure variations.
Although a temperature decrease would normally accompany a pressure decrease,
if these two environmental factors are independently controlled, a situation could
occur where pressure increased at the same time that temperature decreased.
In this event, the errors would be additive, so it is desirable to control both
temperature and pressure to tighter limits than shown on the curves of Figure 4.
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