Determination of Disposed-Upper-Stage Attitude Motion by Ground-Based Optical Observations

The results of an observation campaign devoted to the determination of the rotational state of uncontrolled disposed upper stages by ground-based optical observations are presented. The photometric analysis is performed to extract light curves from photographs obtained by a camera based on charge-coupled devices. The rotation-axis direction and rotation period are determined comparing measurements with theoretical predictions obtained in the simplifying assumption of cylindrical diffusely reflecting cylinders. The angular speed is evaluated by the light-curve period. The direction of rotation axis is evaluated by measuring the difference between the maximum and minimum apparent magnitude of disposed upper stages. This evaluation can be performed from a single observing site by combining measurements collected during a suitable observation time span. The results achieved for two orbiting objects are reported showing a good agreement between determinations obtained in completely different observation geometries.