Orbit Determination of the Dawn Spacecraft with Radiometric and Image Data

Abstract

The orbit of the Dawn spacecraft around asteroid 4 Vesta has been reconstructed using radiometric measurements and image control points. Image control points are introduced as a new measurement type because they constrain the orbit in the along- and crosstrack directions, whereas radiometric measurements provide a stronger constraint in the radial direction. Image control points are available whenever two image footprints on the surface overlap. The measurement uncertainty of images is limited by pixel scale that, in the case of the Dawn mission at Vesta, is between 20 and . The obtained image constraint residual root mean square is approximately the pixel scale for all mission phases. Radiometric residual root mean square spanned from 0.07 to for Doppler and from 0.7 to 1.5 m for range measurements. Radiometric and image constraint residual root-mean-square values are comparable to those reported by the Dawn Science Team using independent software and processing methodology. Improvements as a result of including image control points are largest in the along- and crosstrack directions during the survey phase of the mission. Agreement between the current orbit reconstruction and the trajectory archived by the Dawn Gravity Science Team improves from several kilometers with radiometric measurements to hundreds of meters when image control points are included.