The ideal mounting system for a cartographic camera would keep that 
camera aligned with the true vertical at all times. The direction of true verti- 
cal is defined by a plumb bob hanging from a stationary pivot. In the presence 
of the aircraft r'ntions in six degrees of freedom, and of the dynamic disturb- 
ances introduced b:y the camera operation, this ideal is very difficult of attain- 
ment. As a result, it is necessary to define some level of allowable error to 
serve as a practical design goal for such a system. A study of this problem 
has shown that a reasonable goal for photogrammetric applications would be 3 
minutes of arc maximum deviation from true vertical. Now if the errors are 
allowed to grow to this value, another requirement must be imposed. Since we 
are using the system to support a camera, the picture quality must be consid- 
ered. Motion within the allowed limit of 3 minutes of arc must be of sufficiently 
low rate as to avoid the degradation of resolution. Generally speaking, the mo- 
tion must be limited to the order of 10 to 20 seconds of arc during the exposure 
period! y 
The requirements set forth above have been met by a system designed 
by The Aeroflex Corporation. It consists of a torquer driven camera mounting 
system using the PVRU (Photogrammetric Vertical Reference Unit) as a refer- 
ence. The camera mounting system consists of a set of gimbals supporting the 
camera at its center of gravity. Also carried by the gimbals is a reference 
which indicates the deviation of the gimbals from vertical. This signal is used 
to apply current to a torquer which drives the gimbal in the direction to reduce 
the deviation. Such a mount system is capable of preventing any of the aircraft 
(2) 
or camera disturbances from moving the camera and degrading its resolution 
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