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distances and with known dimensions are also being employed both in the 
calibration of the lens and the calibration of the completed vidicon cameras. 
The 25 point reseau etched on the surface of the vidicon face plate provides 
the basic geometric control; controlling scale factors and total distortions, 
whether optical, electronic, or a combination of both, from recording of 
the object by the camera to the photographic display on the ground receivers. 
The photography from the two vidicon cameras can provide stereoscopic data; 
the known base length between their axes, the calibrated focal length at the 
selected focus, and the known pointing of the observing mirrors providing 
the necessary control. 
Of primary importance is the environmental testing which proves both the 
design adequacy and the geometric reliability of functioning under extreme 
environment. The functioning cameras will be subjected to all simulated 
environments under which they will operate: the high vacuum and the radiation 
of outer space, the vibrations and shock of a spacecraft launch; modern 
testing where image quality and geometric data are the criteria by which 
performance and reliability may be evaluated prior to the important mission. 
One of the well-known drastic environments to which the cameras will be 
subjected is the large temperature variations on the moon. Simulated tests 
have already resulted in redesign of the lens cells. In particular, the 
mating of focusing threads must be quite "sloppy" to avoid binding at extreme 
temperatures. Such a condition normally penalizes photogrammetric precision 
and the investigation of the geometric variables due to this change has inc reased 
the quantity of testing. 
This is only a small part of an extremely interesting project. As of this date, 
most of the photogrammetric problems of the spacecraft have been met and 
solved in such a manner that the basic accuracy of information televised on 
the moon and relayed to earth will, when reconstructed in photographic form, 
be geometrically significant. At this stage, it can be predicted that vidicon 
cameras will truly assume a photogrammetric role in the exploration of space. 
That they will perform reliably is, finally, a matter of record. 
Until that not too far distant day when film exposed on the moon can be reclaimed, 
processed and analyzed on earth, vidicon gathered data must suffice. We 
can expect, however, that as a result of the information gleaned from these 
rapidly approaching surveys, that new and improved photogrammetric equipment 
will be developed to serve this human endeavor and that the information obtained 
with this equipment will approach or equal that obtained with our present high 
quality photogrammetric cameras.