No abstract

The International Earth Rotation and Reference Systems Service (IERS) Rapid Service/Prediction Center (RS/PC) has made several improvements to its combination and prediction products since the last Journées conference in 2007. These improvements are due to the inclusion of new input data sources as well as modifications to the combination and prediction algorithms. These changes and their impact on the users of the RS/PC data are presented.

This paper documents the development of a pitch bias momentum system and the optimal control or Linear Quadratic Regulator (LQR) design procedure developed for a Mixed-Mode Control Strategy to accommodate the loss of up to three reaction wheel assembly (RWA) mounted in a skewed four-for-three configuration. The paper contains three major sections:(1) description of the spacecraft linearized model developed for the three axes pitch bias momentum system, (2) optimal controller design procedure for various types of actuators (i.e., RWA, Torquer Bars, and Thrusters), and (3) closed-loop system performance subject to both normal and failure modes. Design guidelines on how to tune the Q and R weighting matrices subject to RWAs, magnetic torquer bars (MTBs), and thrusters are also summarized as design notes to assist designers in selecting the right set of [Q and R] matrices so that a robust control performance can be achieved. Linearized Pitch Bias Momentum Model