Phobos and Deimos control networks

Abstract Global control networks of 98 surface features on Phobos and 53 on Deimos were established and measured in Viking Orbiter images of the Martian satellites. Photogrammetric triangulation techniques were used to determine the body-fixed coordinates of the control points and to determine mean tri-axial radii of 13.3 × 11.1 × 9.3 km for Phobos and 7.5 × 6.2 × 5.4 km for Deimos. A forced libration amplitude of 0.8 deg was observed. Expressions for the inertial orientations of the spin axes and prime meridians were also determined.