Browsing by Subject "Artificial satellites--Control systems"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Generalized approach to navigation of spacecraft formations using multiple sensors(2006) Holt, Greg Nate; Lightsey, E. GlennAn investigation was performed to evaluate sensor suitability and performance for formation flying in a variety of spaceborne environments. This was done as a precursor to the development of strategies for novel uses of satellite formations in environments other than Low Earth Orbit. Sensor models were developed to allow for a uniform treatment in processing range measurements. A formation simulation environment was then produced which included representative formation geometries, sensor noises, and navigation filters. The simulated formations included Low-Earth, highly elliptical, and libration point orbits. Equations of motion were modified to account for more accurate propagation of elliptical orbits, and an estimator was designed that allowed for large propagation times without GPS measurements. A high-accuracy transponder measurement was added and evaluated to give improved performance to accuracies of a few meters. A similar study was performed for the libration point orbit without the capability to track GPS signals.Item Navigation and control of large satellite formations(2004) Bamford, William Alfred; Lightsey, E. GlennIn recent years, there has been substantial interest in autonomous satellite formations, driven by the new technologies that enable smaller and cheaper spacecraft. Formation flying allows for mission designs, such as stereoscopic imaging, that are impractical or impossible for a single satellite. Much of the current work focuses upon small formations, which can be defined as four or less satellites in a relatively tight grouping. Next generation formations may be composed of more satellites spanning greater spatial distances. The large formation problem becomes more difficult for several reasons, including an increased amount of communication required between the satellites, and orbit perturbations, which become more important as the formation size grows. The purpose of this dissertation is to examine formation flying for large formations, and determine whether or not generalizations can be made linking the large and small formation regimes. In order to model formations with many satellites, a simulation environment was constructed in which different observers, controllers, and formation architectures can be modelled. This dissertation focuses on a decentralized control scheme, but the software is general enough to accommodate a variety of control architectures. Validation of the large formation models is accomplished by initially modelling only a pair of satellites and comparing the results against those found in the literature. As a demonstration of the theoretical results, a real-time, closed-loop, hardware-in-the-loop simulation was constructed using GPS receivers as the measurement source. A large constellation, real-time simulation system was developed that utilized the Internet to connect simulation equipment from research centers in different locations.Item Orbit and attitude state estimation accuracy of an autonomous satellite navigation system(1987) Powell, George Edward, 1963-; Schutz, Bob E.Monte Carlo analysis is employed to evaluate the ability of an autonomous satellite navigation system to determine its orbital and attitude states. Estimation of the orbit and attitude states are treated in a coupled fashion. The navigational system considered consists of a sun sensor, a landmark sensor, and a three-axis rate gyro package. The observation data are processed in a batch-sequential filter which decomposes into an extended Kalman filter as the duration of the batch interval becomes less than the time between two consecutive observations. To avoid singularities in the propagation of the attitude states, quaternions were used to represent the rotation from the body-fixed axes to the inertial coordinate system. However, the attitude was estimated in terms of Euler angles to avoid a singular covariance matrix. Test cases indicate that the estimates of the position in the transverse direction contain the greatest uncertainty