NSSDCA ID: 1969-051A-03
Mission Name: OGO 6This experiment was used to determine the following characteristics of the ionosphere: the ion concentration, the ion composition, the ion temperature, the fast electron flux with energy greater than 9.1 eV, and the horizontal irregularities in the ion concentration. The retarding potential analyzer consisted of a sensor head and an electronics box. The sensor head contained an 8-cm-cylinder with a concentric 2-cm aperture. Charged particles passed through this aperture before striking a solid collector. The path between the aperture and collector was segmented by four grids, whose potentials were controlled by the electronics box. The sensor head was flush-mounted with the front face of the orbital plane experimental package (OPEP). A grounded, gold-plated screen encircled the sensor head. Its purpose was to minimize electric fields parallel to the sensor face. During normal operation, the sensor face was perpendicular to the vehicle velocity vector. The electronics box contained the following: a power supply with several fixed output voltages, an automatic range-changing linear electrometer, a differential amplifier, a linear voltage sweep circuit, and several logic and timing networks. There were two basic modes of operation --an ion-analysis mode and a duct mode. These modes were alternately employed. During both modes, the first two grids were always grounded. The third grid (the retarding grid) was linearly swept from +19.5 to -1.8 V during the ion-analysis mode. This yielded a profile of ion current as a function of voltage, which was used in determining ion temperature and composition. During the duct mode, when small horizontal gradients in ion concentration were examined, the retarding grid was maintained at -1.8 V. The fourth grid (the suppressor grid) was always maintained at -9.1 V. This grid was used to suppress photoemission from the collector. (All voltages given are with respect to vehicle ground.) A complete cycle time of either 40 or 10 s could be selected for both modes by ground command. In a 10-s cycle time, for example, the first 5 s were used for the ion-analysis mode, and the second 5 s were used for the duct mode. During real-time readout, the 10-s cycle period was automatically invoked, since higher data rates were employed. The spatial resolution was from 40 to 160 m, depending on the cycle time selected. The experiment was first turned on during orbit 20. Three weeks after launch (June 22, 1969), a failure occurred in the solar paddle array. This gave the vehicle a negative potential of more than 20 V when the paddles were exposed to sunlight. Under this condition, reliable ion temperature, ion composition, and photoelectron flux data could not be obtained except upon spacecraft entry into eclipse, when the vehicle potential recovered quite rapidly. However, ion concentration and duct mode were still valid during sunlight. In October 1969, a change occurred in the solar paddle array. This caused the vehicle potential to diminish to the extent that ion temperature and dominant component ions could be determined even in sunlight. During each eclipse, the vehicle potential returned to normal, and complete data were obtained during approximately 30% of each orbit. The performance of the instrument was excellent from turn-on, and the experiment yielded excellent data. It was normally operated 100% of the time. The experiment was turned off during June 1971. A good description of the experiment is given in W. B. Hanson et al., "Plasma measurements with the retarding potential analyzer on OGO 6," J. Geophys. Res., v. 75, pp. 5483-5501, Oct. 1970. NSSDC has all the useful data that exist from this investigation.
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Name | Role | Original Affiliation | |
---|---|---|---|
Mr. T. W. Flowerday | Other Investigator | University of Texas, Dallas | |
Prof. William B. Hanson | Principal Investigator | University of Texas, Dallas |