Control Networks of the Galilean Satellites - A Progress Report
M. E. Davies, T. R. Colvin (RAND), A. S. McEwen, C. B. Phillips (Univ. Arizona), J. Oberst, W. Zeitler, P. Schuster, G. Neukum (DLR), P. Thomas, J. Veverka (Cornell Univ.), G. Schubert (UCLA), M. J. S. Belton (NOAO), Galileo SSI Team
A control network is a table of coordinates of points identified and measured on images of a body. An analytical triangulation program is used to compute the coordinates of points and to improve camera-pointing angles. Control networks are used to compile planimetric and topographic maps. The first step in computing control networks of ellipsoidal bodies, like the Galilean satellites, is to calculate the body's mean radius and center of mass. Table I. gives results of these computations using data from Voyager and Galileo.
Table I. Control Network Status.
The cartographic reference surfaces (datums) of the Galilean satellites are tri-axial ellipsoids. Their axes are approximated using measurements of gravitational coefficients obtained during the Galileo flybys and using the ratio of centrifugal to gravitational acceleration at the satellite's equator.
Table II. Tri-axial Reference Surfaces.
References:
Anderson, et al., Science 272, 709-712, 1996; Science 276, 1236-1239,
1997; Nature 384, 541-543, 1996; Nature 387, 264-266,
1997.
Hubbard and Anderson, Icarus 33,336-341, 1978.
Zharkov, et al., Icarus 61, 92-100, 1985.