Methods for dynamic parameters identification and vibrations estimation of large spacecraft with flexible structures are reviewed. Different approaches to the structural deviation determination and to the vibration frequency identification by processing measurements from the onboard sensors are compared. Measuring devices and sensors for the motion estimation of large nonrigid structures are reviewed.

The problem of small tetrahedral satellite formation maintenance in a Low Earth Orbit is being considered. The main purpose is to develop a simple algorithm for tetrahedron control via atmospheric drag. To design a controller, the direct Lyapunov method is used. The control obtained is suitable for tetrahedral formation maintenance, with an average distance of about 1 km. During the controlled motion, the geometric characteristics of the tetrahedron are preserved.

Attitude motion reconstruction of the Technological NanoSatellite TNS-0 #2 during the last month of its mission is presented in the paper. The satellite was designed to test the performance of the data transmission via the Globalstar communication system. This system successfully provided telemetry (even during its atmosphere re-entry) up to an altitude of 156 km. Satellite attitude data for this phase is analyzed in the paper. The nominal satellite attitude represents its passive stabilization along a geomagnetic field induction vector. The satellite was equipped with a permanent magnet and hysteresis dampers. The permanent magnet axis tracked the local geomagnetic field direction with an accuracy of about 15 degrees for almost two years of the mission. Rapid altitude decay during the last month of operation resulted in the transition from the magnetic stabilization to the aerodynamic stabilization of the satellite. The details of the initial tumbling motion after the launch, magnetic stabilization, transition phase prior to the aerodynamic stabilization, and subsequent satellite motion in the aerodynamic stabilization mode are presented.

We investigate a class of Lyapunov-based attitude control algorithms dedicated to keep-out zone avoidance. They utilize convex representations of the allowed attitude and potential barriers that are also supposed to be convex. We show that such parameterization is not actually convex, and that suggested control generates additional asymptotically stable equilibria.