Commission IV, WG IV/8 KEY WORDS: Enceladus, photogrammetry image processing, 3D control point network, estimation of shape and forced libration
ABSTRACT:A new global control point network was derived for Enceladus, based on Cassini and Voyager-2 image data. Cassini images were taken from 2005 to 2014, for Voyager we have only one flyby in the middle of 1981. We have derived 3D Cartesian coordinates for 1128 control points as well as improved pointing data for 12 Voyager and 193 Cassini images in the Enceladus-fixed coordinate system. The point accuracies vary from 55 m to 2900 m (average point accuracy 221 m). From tracking of the control points we detect a librational motion described by a model which includes 3 different periods and amplitudes (Rambaux et al., 2011). We determine the amplitudes for each term. Our new control point network has a higher number of point measurements and a higher accuracy than previous data (Giese et al., 2014).
Lunar Reconnaissance Orbiter Camera (LROC) system consists of a Wide Angle Camera (WAC) and Narrow Angle Camera (NAC). NAC images (~0.5-1.7 m/pixel) reveal details of the Luna-21 landing site and Lunokhod-2 traverse area. We derived a Digital Elevation Model (DEM) and an orthomosaic for the study region using photogrammetric stereo processing techniques with NAC images. The DEM and mosaic allowed us to analyze the topography and morphology of the landing site area and to map the Lunokhod-2 rover route. The total range of topographic elevation along the traverse was found to be less than 144 m; and the rover encountered slopes of up to 20 degrees. With the orthomosaic tied to the lunar reference frame, derived coordinates of the Lunokhod-2 landing module, its final position and overnight stop points. We identified the exact rover route by following its tracks and determined its total length as 39.16 km, more than was estimated during the mission (37 km), which until recently was a distance record for planetary robotic rovers held for more than 40 years. 126Lunokhod-2 moved at two distinct speeds: 0.8 km/hour and 2.0 km/hour (Kemurdzhian et 127 al., 1993). Turning of the vehicle was achieved by varying the rotation of the wheel on the right 128 and left sides, respectively, and by changing the direction of their rotation. The turning radius of 129 the rover in motion was typically 3 m with wheels turning at different speeds (Kemurdzhian et 130 al., 1993). However, the rover could also turn in place (with its left and right wheels turning in 131 opposite directions) within a radius of 0.8 m. Areas where the rover turned in place can be seen 132 readily in the NAC images. 133
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