Spacecraft Attitude Dynamics and Control

Spacecraft attitude dynamics and control is a study that encompasses kinematics, rigid-body dynamics, linear control theory and orbital environmental effects. This block models attitude dynamics using numerical integration.

Spacecraft use thrusters to propel themselves in specific directions, however this approach has its limitations, including fuel usage and thruster cycle time. An alternative would be relying on inertial properties of their vehicle such as long, thin satellites that tend to align their principal axis with Earth.

Stability Analysis

Students gain an understanding of the natural dynamics that cause spacecraft attitude motion, providing them with the skills to formulate and solve engineering problems. Concepts are introduced via homework assignments and structured class discussions.

Stability analysis is the practice of determining how stable a system is as a function of its control law and actuator parameters, through a combination of theoretical analysis and numerical simulation. System stability can then be compared against closed-loop dynamics to make an assessment.

Over the 10-year history of GRACE double satellite formation for gravity field exploration, 38 impacts of space debris have caused satellites to exit science mode and 7 caused control algorithms to diverge from required accuracy. This paper compares effects of various control algorithms on angular momentum and pointing accuracy after space debris impacts, with Lyapunov control emerging as the winner in most instances.

Stability Estimation

Attitude Determination and Control System is one of the key subsystems on any spacecraft, as any failure in actuators or sensors could have serious repercussions for mission success. Unfortunately, however, there are limited fault detection and diagnosis mechanisms in place.

Model and analyze a rigid spacecraft with inertia matrix uncertainty and external disturbances to perform stability analysis, then develop and apply a sliding mode control law which can stabilize it.

Fault-tolerant attitude estimation using federated unscented Kalman filters has been developed and its performance tested via simulation in the presence of sensor faults. Furthermore, actuator dynamics’ effect on fault detection and isolation was studied. As the results demonstrate that attitude estimation can still function correctly even when some sensors fail, it represents an invaluable contribution to spacecraft attitude estimation research.

Stability Measurement

Stability measurement is an integral component of spacecraft attitude control. To achieve this goal, an example analysis is first conducted, then a basic control law designed to guarantee finite-time stability is developed.

An adaptive nonsingular back-stepping attitude controller has been designed. Analytically it was demonstrated that output feedback spacecraft quaternion and angular velocity are practical predefined-time stable even under conditions of mismatched uncertainty and input saturation.

Additionally, a new double fast terminal sliding mode manifold is proposed to analyze the dynamics of an actuator. A control law is then developed to provide finite-time stability of spacecraft attitude stabilization and its performance is tested via simulations. Simulation results confirm that proposed control law can effectively stabilize spacecraft using actuator dynamics for high precision attitude stabilization.

Stability Control

Spacecraft control systems aim to achieve stable attitudes by employing both passive and active methods that range from spin stabilization to zero momentum three axis stabilization systems. Their designers must minimize disturbance torques caused by non-ideal geometry or atmospheric variations as part of their designs in order to reach this goal.

Simple passive attitude support systems consist of using magnets to orient a satellite. While this allows for relatively high pointing accuracy, its effects are limited by energy minima associated with magnet fields; for more flexible control over energy minima it may be necessary to incorporate dampers made of hysteretic or viscous materials.

These systems often exhibit some degree of instability due to the dampers introducing a force lever arm into the angular velocity equation and creating an unwanted torque disturbance on body axes. To mitigate this effect, try minimizing the host vehicle center of mass to sphere coP distance dCOM0 while simultaneously limiting any subsequent force lever arm effects.

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