NSSDCA ID: 1969-051A-26
Mission Name: OGO 6A horizon-scanning photometer experiment measured the absolute brightness of the yellow sodium D lines and the atomic oxygen green line during day, twilight, and night airglows. These data were used to study the spatial and temporal variations of the airglow emissions and of the atmospheric atomic oxygen concentration. Amplification by a factor of from 10 to 20 in the surface brightness of the airglow emissions was the result of large optical paths due to slantwise observation, allowing some airglow features to be detected that might have been missed in rocket observations. Incident radiation passed through a baffle and was reflected from a plane stepping mirror to a spherical mirror. This spherical mirror then focused the light through a hole in the stepping mirror, and through a cylindrical shutter and two lenses between which was placed an interference filter. The radiation then impinged on a side-window photomultiplier tube. Two filters were switched between the lenses. The maximum transmission of the atomic oxygen green line filter was 0.49 at 5582 A, with a bandpass of 28 A. The sodium filter had a maximum transmission of 0.57 at 5898 A and a bandpass of 24 A. These bandpasses were chosen to make allowance for the range of expected temperature variation. The entrance aperture of the photometer was in the spacecraft main body '+X' was in the direction of motion. In the vertical direction the field of view was 7.1 min of arc, and it was 4.2 deg in the horizontal direction. The stepping mirror, pivoted to scan the sky near the horizon, rotated in 128 steps, with each step producing a change of 7.5 min of arc. Thus a scan was produced that varied the look direction from 10 deg to 26 deg below the horizon in a time interval of 18.4 s. There were two consecutive vertical scans: one from low to high altitude and the other from high to low altitude with a given filter, and then the filter was changed. The output from the photomultiplier tube, was fed to an electrometer. On the most sensitive scale, the dark current produced only a 0.4-volt output, and the photometer sensitivity was 191 rayleighs per volt using the green filter, and 250 rayleighs per volt with the yellow filter. An external light-level monitor closed a shutter between the mirror and lens system when the signal became too large. Every 296 seconds, an internal calibration cycle took place and lasted for about 6 seconds. More experiment details and some results are presented in T. M. Donahue et al., "Distribution of atomic oxygen in the upper atmosphere deduced from OGO 6 airglow observations," J. Geophys. Res., v. 78, n. 28, pp. 6662-6689, Oct. 1973.
Mass: 5.24 kg
Power (avg): 6.7 W
Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office
Name | Role | Original Affiliation | |
---|---|---|---|
Prof. Jacques E. Blamont | Other Investigator | CNRS, Service d'Aeronomie | |
Prof. Thomas M. Donahue | Principal Investigator | University of Michigan | lcrk@engin.umich.edu |