Walter Fichter

Dynamic Momentum BIAS for Yaw Steering

Abstract A combination pointing requirement for a low earth orbit communication satellite antenna system and sun orientation for power accumulation can be met with a momentum biased attitude control that maintains nadir pointing and sustains yaw steering simultaneously. During time intervals when direct yaw sensing is not available, momentum bias systems have successfully been used to provide stabilization for nadir pointing satellites. Such systems, however, restrain vehicle yaw rotations to small perturbations about zero without direct yaw sensing. Those systems use a momentum wheel with fixed alignment along the spacecraft pitch axis, horizon sensors to detect pitch and roll attitude errors and mass expulsion devices for actuation. Such systems preclude yaw steering. This paper develops a control algorithm that maintains the advantage of gyroscopic momentum bias stabilization in addition to a controlled open loop yaw steering.

Control design for generalized normal mode operation of bias momentum satellites

Abstract An attitude controller for a 3-axis stabilized, Earth-oriented bias momentum spacecraft is described, where only 2-axis attitude measurements from the Earth sensor are available. In contrast to classical spacecraft, that are controlled with respect to a fixed orbital Earth pointing reference frame, (possibly large-angle) time-varying reference signals are considered here, i.e. the control task consists of a tracking problem. The controller design consists of a decoupling controller and axis-related PID controllers based on yaw observer estimates.

Attitude and Orbit Control System Design for the Globalstar Telecommunications Satellite

Abstract The attitude and orbit control system (AOCS) for the Globalstar constellation of 48 low-earth-orbit cellular-telephone communication satellites is described. The attitude control system must point the antenna to the earth and rotate the satellite in a prescribed yaw-steering profile so that a single rotation about the solar-array axis can always keep the panels perpendicular to the sun. In addition, the AOCS must provide for safe holding in a sun-pointing mode and be able to control the satellite during orbit-change maneuvers.

Magnetic Attitude- and Angular Momentum Control Design for Momentum BIAS Satellites in Low Earth Orbits

Abstract This paper describes the controller design for a three-axis stabilized bias momentum satellite, that is equipped with one momentum wheel and two magnetic coils for actuation purposes, and a two-axis infrared Earth sensor. Such a low cost equipment configuration can preferably be used for commercial communication systems, consisting of satellites with less stringent pointing requirements, distributed in several orbits with an inclination of about 50 degrees.

Advanced Attitude-and Orbit Control Concepts for 3-Axis-Stabilized Communication and Application Satellites

Abstract The rapidly increasing demands and the large variety of technical and economic requirements for future communication-and application satellites necessitate an advance of the efficiency in all areas of system development. In addition to technical performance improvements, optimal use of equipment, and ease of operability especially stringent economic boundary conditions are to be met. Such ambitious goals cannot be achieved on the basis of efforts made on the level of an individual subsystem and its equipment only but requires a well balanced overall system approach. Presently, based on a cooperation agreement between DASA/MBB and Aerospatiale companies, joint efforts are being undertaken towards an optimized approach of this kind, within the so-called “Spacebus Improvement Program” (SIP). The key issue of the approach adopted is an Integrated Control and Data System (ICDS), which combines the versatility and flexibility inherent to the Attitude-and Orbit Control Subsystem (AOCS) with the Data Management and Control (DMC) tasks, making best possible use of modem equipment technology and onboard processing capabilities.