than 10° and the total power input will remain constant within a 
few percent throughout the life of the satellite. 
6. Tracking Accuracy 
When the TRANSIT program was first proposed, the most 
serious technical questions raised concerned the feasibility of 
tracking the satellites with sufficient accuracy. Obviously, to 
determine your position on earth by reference to the position of 
a satellite, it is necessary that the position of the satellite, 
at a given time, be known to higher accuracy than the accuracy 
with which your own position is to be determined. At the time 
the initial TRANSIT program proposal was being considered, typical 
satellite tracking or prediction errors ranged from 5 miles to as 
much aS 50 miles. There was a wide spread belief among even well 
informed people that there were mysterious or at least unpredict- 
able forces of large magnitude acting on satellites which wuld 
for years prevent orbit prediction with an accuracy of better than 
a number of miles. Fortunately, most of the difficulties of that 
period were a result of poor measurement rather than of a reflec- 
tion of basic unknowns. It is true that there were and still are, 
areas of ignorance concerning the precise formulation of the forces 
acting on a near earth satellite (for example, the proper descrip- 
tion of the earth's gravitational field is not too well known) but 
the effect of these uncertainties on the trajectory is one or two 
tenths of a mile rather than a number of miles. The fact that 
present knowledge of the forces acting on a satellite is sufficiently 
accurate to enable tracking and short term (12 hour) prediction of 
Satellite position to an accuracy of a few tenths of a mile has been 
shown conclusively by our tracking experience with TRANSIT 1-B and 
TRANSIT 2-A. 
One way to judge the accuracy with which orbit deter- 
mMinations are made is simply by observing the consistency of the 
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