Helmut Bittner

DESIGN OF REACTION JET ATTITUDE CONTROL SYSTEMS FOR FLEXIBLE SPACECRAFT

Abstract In reaction jet attitude control systems Pulse-Width-Pulse-Frequency (PWPF-) or Pseudo-Rate (PR-) Modulators, which include nonlinear (relay) characteristics, are commonly used to operate the thruster valves. For the stabilization of flexible space vehicles, regulator configuration, control and modulator parameters have to be carefully matched to meet loop performance requirements and to ensure stability of structural modes of vibration. Restrictions are imposed on the choice of free parameters by the minimum pulse bit size, limit cycle rates, admissible number of thruster operations and disturbance torque variation over mission life time or attitude sensor noise. A unified approach for design and stability analysis of such nonlinear attitude control systems is presented, which makes use of normalized modulator design and performance parameters.

The Attitude and Orbit Control Subsystem Of the EUTELSAT II Spacecraft

Abstract This paper deals with the EUTELSAT II Attitude Determination and Control Subsystem (ADCS), presently under development at MBB. The spacecraft is three axis stabilized during all phases of the mission, from launcher separation up to graveyard de-orbiting. During all geosynchronous operations, the ADCS is based on the momentum bias principle. An overview of the EUTELSAT II platform and associated requirements on the ADCS is given. The subsystem equipments are presented, including sensors, control electronics and actuators. The main characteristics of the ADCS are introduced and a mode description is provided. Modes include new design features like an Earth Re-acquisition Mode based on gyro reference (ERAMG) and a Software Safe Mode (SSM) in order to minimize outage durations. A Nutation Angular Momentum Control mode (NAMC) is implemented to enhance the classical WHECON principle and cope with high disturbance torques and fine yaw pointing. Finally the development, qualification and test of the subsystem is presented and representative simulation results are shown.

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.

Investigation of a Flat Earth Guidance Law Using a Quadratic Injection Criterion and Inflight Vehicle Parameter Identification

Abstract This paper describes the formulation and simulation testing of a Flat Earth Guidance Law using a quadratic injection criterion and inflight vehicle parameter identification and updating. It avoids the usual instability close to injection without necessitating a separate injection guidance routine and eliminates the distortion of the attitude law at injection due to vehicle parameter deviations from nominal. It is suited for injection into circular and elliptical orbits. Apart from effectiveness and parameter sensitivity of the guidance law the discussion of results also covers the practical aspects of implementation in an onboard computer with limited resolution accuracy.

Effectiveness of Different Optimum Filtering Techniques for the Particular Example of Radio Guidance of the Third Stage of Europa 1 Carrier Vehicle

Summary For the particular example of the radio guided third stage of EUROPA 1 carrier vehicle two different optimum filtering techniques have been compared: The augmented state version actually implemented in the downrange guidance computer (formulated in ref. 3) and a measurement differencing type filter (ref. 4 and 5). The problem is nonlinear and the noise superimposed on state components and measurements is assumed to be sequentially correlated. Six downrange guidance station measurements (two short base interferometer-, two long base interferometer-, range- and range rate measurements) are used to update the state information once in a second (continuous time-discrete data problem). Identical random sample functions have been used in both cases to drive the noise models of the system, allowing for a comparison of the estimation errors and covariances at individual instances. The two filter versions are equivalent as for the final estimation accuracy of vehicle position- and velocity components, the transient behaviour, however, is different. For the nonlinear problem under discussion, the implementation of the measurement differencing filter does not save computation time as compared to the augmented state version, since the time gained in processing the reduced state vector and covariance matrix is used up again by additional computations required.