SATELLITE-TRACKING PROGRAM — HAYES 355 



motion of this line produced by the flattening of the earth, but since 

 they did not know with sufficient accuracy what the flattening was, 

 they did not trust the extrapolation they obtained this way. 



After the first week or so the staff became a little more sophisticated. 

 Instead of going to the map, they would start with a desk computer. 

 The problem was again one of trigonometry, of finding the position 

 of the satetille, plotting the positions of the satellite corresponding to 

 the observations, and then trying to fit lines through them so that 

 they could predict ahead. The major difficulty was that the orbital 

 period was shortening fairly drastically, so they needed a good way 

 of determining how the period changed with time to allow them to 

 extrapolate ahead. 



When Dr. Luigi Jacchia of the Harvard Meteor program returned 

 from Italy late in October, Dr. Whipple asked him to take a hand 

 in the computations work. He immediately considered what stop- 

 gap measure might best utilize Moonwatch and other observations 

 to derive more accurate and more automated predictions. He devised 

 the so-called subsatellite program that could be fed into an electronic 

 computer to reduce each observation. From a fairly accurate orbit — 

 and by this time the Observatory had such orbits — the program would 

 compute for each observation the position of the node and the time 

 of the crossing of the equator. Then, from a diagram based on these 

 two quantities, the program would allow one to follow the object and 

 to make predictions for a fairly long period of time. After some 

 preliminary experiments with the program by hand computation. Dr. 

 Jacchia asked Eobert Briggs to set it up for the IBM-650, an elec- 

 tronic computer with which he was familiar. By late November, the 

 Observatory was able to reduce an observation in something less than 

 one minute of machine time and to prepare reasonably precise pre- 

 dictions of transit of Satellites 1957 Alpha and 1957 Beta. 



The program developed by Jacchia could not be used by itself to 

 derive orbital elements. There were five other orbital elements that 

 still had to be determined (see part 1 of this history) . The program 

 could derive discrepancies between the observations and the assumed 

 orbital elements, in much the same way that Lautman's program 

 was later to operate. It was now a question of taking these discrep- 

 ancies and plotting them in order to decide which orbital element 

 most needed correction, improve that one, and then continue this 

 analysis of the observations again to find a new set of discrepancies ; 

 and so on. Although, in a sense, the program was, as Dr. Hynek 

 described it, a "quick and dirty approach," for the next year and a half 

 it was the work horse of the Computations and Analysis Division. 



Jacchia found that he had unofficially taken on the task of pre- 

 dicting the positions of the first two Russian satellites, which he con- 

 tinued to do until April 1958, and which resulted in his writing the 



