[Previous] | [Session 53] | [Next]
G. R. Carruthers, M. A. Finch, G. L. Dixon (Space Science Division, Naval Research Laboratory), T. D. Seeley (Naval Center for Space Technology, Naval Research Laboratory)
The Global Imaging Monitor of the Ionosphere is one of 9 space research and technology instruments aboard the Air Force Space Test Program's Advanced Research and Global Observation Satellite, launched into a sun-synchronous polar orbit on February 23, 1999. GIMI began routine on-orbit operations in late May, 1999.
GIMI contains two far-UV electron-bombarded CCD cameras having 9°-square fields of view and about 1 milliradian resolution. Although the primary objectives of GIMI are studies of Earth's upper atmosphere and ionosphere, it is also being used to image star fields in the far UV. The objective is to survey as much of the sky as possible, observing both point and diffuse sources, as well as more detailed observations of objects of special interest. The camera currently being used for this survey is sensitive in the wavelength ranges 131-160 and 131-200 nanometers.
Since ARGOS is an Earth-center-stabilized spacecraft, GIMI uses a gimbal system to compensate for the orbit rate of 0.059° per second, so that celestial targets remain fixed in the camera field of view during exposure times of up to 110 seconds. Celestial observations are made only in the orbit plane (which precesses eastward about 1° per day) in the Earth-shadow portions of each orbit. The usable viewing direction zenith angle range is 70° to 105°. The current observing program, begun in the fall of 1999, uses GIMI viewing in the aft (anti-velocity) direction, allowing coverage the northern (celestial) polar cap region (down to ecliptic latitude ~ +35°), and will require one year to complete. A following, similar survey viewing in the forward (velocity) direction, beginning in the fall of 2000, will cover the southern celestial polar cap region (up to ecliptic latitude ~ -35°). Typical images obtained during the survey are displayed, and status and plans for further observations, image calibration, and data analysis are provided.