Apollo experience report: Guidance and control systems - Digital autopilot design development

The development of the Apollo digital autopilots (the primary attitude control systems that were used for all phases of the lunar landing mission) is summarized. This report includes design requirements, design constraints, and design philosophy. The development-process functions and the essential information flow paths are identified. Specific problem areas that existed during the development are included. A discussion is also presented on the benefits inherent in mechanizing attitude-controller logic and dynamic compensation in a digital computer

Adaptive control of large space structures using recursive lattice filters

The use of recursive lattice filters for identification and adaptive control of large space structures is studied. Lattice filters were used to identify the structural dynamics model of the flexible structures. This identification model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures is control engaged. This type of validation scheme prevents instability when the overall loop is closed. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods. The method uses the Linear Quadratic Guassian/Loop Transfer Recovery (LQG/LTR) approach to ensure stability against unmodeled higher frequency modes and achieves the desired performance

A Kinematic Approach to Determining the Optimal Actuator Sensor Architecture for Space Robots

Autonomous space robots will be required for such future missions as the construction of large space structures and repairing disabled satellites. These robots will need to be precisely controlled. However, factors such as manipulator joint/actuator friction and spacecraft attitude control thruster inaccuracies can substantially degrade control system performance. Sensor-based control algorithms can be used to mitigate the effects of actuator error, but sensors can add substantially to a space system’s weight, complexity, and cost, and reduce its reliability. Here, a method is presented to determine the sensor architecture that uses the minimum number of sensors that can simultaneously compensate for errors and disturbance in a space robot’s manipulator joint actuators, spacecraft thrusters, and reaction wheels. The placement and minimal number of sensors is determined by analytically structuring the system into “canonical chains” that consist of the manipulator links and spacecraft with force/torque sensors placed between the space robot’s spacecraft and its manipulators. These chains are combined to determine the number of sensors needed for the entire system. Examples of one- and two-manipulator space robots are studied and the results are validated by simulation

A novel fault-tolerant control strategy for near space hypersonic vehicles via least squares support vector machine and backstepping method

Near Space Hypersonic Vehicle (NSHV) could play significant roles in both military and civilian applications. It may cause huge losses of both personnel and property when a fatal fault occurs. It is therefore paramount to conduct fault-tolerant research for NSHV and avoid some catastrophic events. Toward this end, this paper presents a novel fault-tolerant control strategy by using the LSSVM (Least Squares Support Vector Machine)-based inverse system and Backstepping method. The control system takes advantage of the superiority of the LSSVM in solving the problems with small samples, high dimensions and local minima. The inverse system is built with an improved LSSVM. The adaptive controller is designed via the Backstepping which has the unique capability in dealing with nonlinear control systems. Finally, the experiment results demonstrate that the proposed method performs well

Analytical landing trajectories for embedded autonomy

This paper considers an optimal guidance law for the initial braking phase of a soft landing mission on a celestial body without atmosphere in which boundary conditions on height and velocity are specifed. The optimal lander attitude for the minimum fuel landing problem is found. An analytic optimal trajectory is achieved by expanding the thrust acceleration, gravitational acceleration and the cosine of the vertical attitude angle to a high-order polynomial. Coefficients of these polynomials are obtained from the boundary conditions. A fixed gain control law and a direct adaptive control law are then developed to track the analytical reference trajectory. Finally, a mission scenario is presented to illustrate the accuracy of the analytical trajectory and validity of the control laws developed. The use of direct adaptive control for embedded autonomy will be directly contrasted against a traditional fixed gain controller, using a Lunar landing scenario. The advantage of the direct adaptive control approach is that it does not require system monitoring to detect thruster failure and can adjust its gain automatically. As such, direct adaptive control combined with the developed analytical solution enables autonomy to be embedded within the lander guidance and control system. In addition, it is shown that direct adaptive control increases the probability of lander survival through faster transient response and stability than a traditional fixed gain controller with system level failure detection and recovery

The reduced order model problem in distributed parameter systems adaptive identification and control

The research concerning the reduced order model problem in distributed parameter systems is reported. The adaptive control strategy was chosen for investigation in the annular momentum control device. It is noted, that if there is no observation spill over, and no model errors, an indirect adaptive control strategy can be globally stable. Recent publications concerning adaptive control are included

Design of an Attitude Control System for a Spacecraft with Propellant Slosh Dynamics

The presence of propellant slosh dynamics in a spacecraft system during a maneuver leads to attitude control system (ACS) performance degradation resulting in attitude tracking errors and instability. As spacecraft missions become more complex and involve longer durations, a substantial propellant mass is required to achieve the mission objectives and perform orbital maneuvers. When the propellant tanks are only partially filled, the liquid fuel moves inside the tanks with translational and rotational accelerations generating the slosh dynamics. This research effort performs a comparative study with different optimal control techniques and a novel application of a model reference artificial immune system adaptive controller (MRAIS). A linearized model of a realistic spacecraft dynamic model incorporating propellant slosh is derived utilizing the mass-spring analogy. Simulations with the linearized models assist in control law development to achieve the control objective: to suppress the fuel slosh dynamics while obtaining the desired attitude. These control laws are then tested with the nonlinear equations of motion for a spacecraft with propellant slosh dynamics to evaluate the ability of the models to design an attitude control system. Monte Carlo analysis is also applied to characterize the performance of each controller and determine the most significant parameters that cause instability issues. The Model Reference Artificial Immune System has superior performance in comparison to the baseline optimal control systems and is more robust to system instabilities, actuator failures, and aggressive maneuvers

Space science/space station attached payload pointing accommodation study: Technology assessment white paper

Technology assessment is performed for pointing systems that accommodate payloads of large mass and large dimensions. Related technology areas are also examined. These related areas include active thermal lines or power cables across gimbals, new materials for increased passive damping, tethered pointing, and inertially reacting pointing systems. Conclusions, issues and concerns, and recommendations regarding the status and development of large pointing systems for space applications are made based on the performed assessments

Technology for large space systems: A bibliography with indexes (supplement 10)

The bibliography lists 408 reports, articles and other documents introduced into the NASA scientific and technical information system to provide helpful information to the researcher, manager, and designer in technology development and mission design in the area of large space system technology. Subject matter is grouped according to systems, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

Development of Fault Tolerant Adaptive Control Laws for Aerospace Systems

The main topic of this dissertation is the design, development and implementation of intelligent adaptive control techniques designed to maintain healthy performance of aerospace systems subjected to malfunctions, external parameter changes and/or unmodeled dynamics. The dissertation is focused on the development of novel adaptive control configurations that rely on non-linear functions that appear in the immune system of living organisms as main source of adaptation. One of the main goals of this dissertation is to demonstrate that these novel adaptive control architectures are able to improve overall performance and protect the system while reducing control effort and maintaining adequate operation outside bounds of nominal design. This research effort explores several phases, ranging from theoretical stability analysis, simulation and hardware implementation on different types of aerospace systems including spacecraft, aircraft and quadrotor vehicles. The results presented in this dissertation are focused on two main adaptivity approaches, the first one is intended for aerospace systems that do not attain large angles and use exact feedback linearization of Euler angle kinematics. A proof of stability is presented by means of the circle Criterion and Lyapunov’s direct method. The second approach is intended for aerospace systems that can attain large attitude angles (e.g. space systems in gravity-less environments), the adaptation is incorporated on a baseline architecture that uses partial feedback linearization of quaternions kinematics. In this case, the closed loop stability was analyzed using Lyapunov’s direct method and Barbalat’s Lemma. It is expected that some results presented in this dissertation can contribute towards the validation and certification of direct adaptive controllers