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Explorer I data acquisition
A tabulation of station passes and data received for the first day of the satellite’s life shows the general pattern of initial operations, during which time the ground stations were working out the operational and equipment problems associated with the use of a new network.7,8 That tabulation is shown as Table 11.1.
A comprehensive assessment of the complete data acquisition history was assembled from the final Explorer I data tabulation.9 In that assessment, recordings were counted if the signal quality was good enough that beginning and ending times could be ascribed for the reception of a recognizable modulation of the signal. From 1 through 11 February, that is, until the high-power transmitter began to fail on 12 February, there were 394 such recordings. After 11 February, the recordings totaled 234, nearly all from the low-power transmitter. A summary of the recording history is as follows: [8]
OPENING SPACE RESEARCH
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TABLE 11.1 Explorer I Data Reception for 1 February 1958
a The data quality indicators are as follows: A, noise-free data; B, data readable within extended segments; C, regular noise fade patterns, with clear segments between fades; D, noise on all data; E, very noisy data, barely readable; F, no readable data. b All times are universal time (UT). Add five hours for EST, etc. |
were reactivated as soon as the high-power signal was again observed, there were fewer stations on line during that period, and they appear not to have been scheduled as heavily. It is also possible that the high-power system was not transmitting at full power.
CHAPTER 11 • OPERATIONS AND DATA HANDLING 293
• Low-Power System
о From 1 through 13 February, a daily average of 12.7 recordings of the low – power signal was obtained. The lower recovery rate for the low-power system (compared with that for the high-power system) was due to the fact that the high-power signal could be read by all 17 Microlock and Minitrack ground stations, whereas only 7 (the six Microlock stations and the Minitrack station at Woomera, Australia) were equipped to receive the low-power signal. Furthermore, the low-power signal, being weaker, was intrinsically harder to read.
о From 14 February through cessation of the low-power signal on 14 April, the data recovery rate averaged 9.8 passes per day. The lower recovery rate for the low-power signal during that period, compared with that in the earlier period, is ascribed to the difficulty in acquiring and tracking the low-power signal in the absence of the high-power signal. When both signals were present, the common practice was to do the initial antenna pointing using the high – power signal. After the demise of the high-power system, that had to be done exclusively with the weaker signal.
о The distribution of successful recordings during that period ranged from 4 to 15 per day, with a peak recovery rate around 20 March. That pattern probably reflected the changing position of the satellite’s apogee relative to the ground station locations.
Not all of the cases reported above resulted in scientifically useful data. Frequently, when the signals were weak due to attempts to acquire the data at very low elevation angles, the modulation of the signal caused by the combination of the antenna pattern and satellite motion resulted in additional degradation. Of the total number of cases where the carrier was detected, about half of them produced data sufficiently clear to be useful in the scientific analyses.