Parameter identification of large spacecraft systems based on frequency characteristics

In this paper we describe parameter identification for an in-orbit satellite. Actual experimental results are described for the Low Atmospheric Control Experiment (LACE) spacecraft. This is a low earth orbit satellite that was launched into a circular orbit. Its structure consists of a central rigid body or bus with three deployable booms. The first boom is the gravity gradient boom while the second is the retro-reflector boom. We accomplished the identification of the structural modes and damping factors of the spacecraft in orbit. A systems approach was used to analyze the experiment and present identification techniques utilizing the frequency characteristics of the Hankel operator. Frequency domain error bounds and time domain error bounds were considered. The experiment was performed on a satellite in conjunction with the Naval Research Laboratory. The experiment utilized ground based laser illumination with Doppler shifted returns and identified three of the lowest vibration modes. The accuracy of the methods was extremely good.