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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Magnetic Attitude Control of Microsatellites In Geocentric Orbits

Dutia, Jiten 18 March 2013 (has links)
Attitude control of spacecraft in low Earth orbits can be achieved by exploiting the torques generated by the geomagnetic field. Recent research has demonstrated that attitude stability of a spacecraft is possible using a linear combination of Euler parameters and angular velocity feedback. The research carried out in this thesis implements a hybrid scheme consisting of magnetic control using on-board dipole moments and a three-axis actuation scheme such as reaction wheels and thrusters. A stability analysis is formulated and analyzed using Floquet and Lyapunov stability theorems.
12

Investigation of Active Vibration Suppression of a Flexible Satellite using Magnetic Attitude Control

Findlay, Everett 07 December 2011 (has links)
The problem of attitude control of a flexible satellite using magnetic attitude control is investigated. The work is motivated by JC2Sat - a joint CSA and JAXA mission whose main purpose is a proof of concept of two satellites performing differential drag formation flying. The impact of additional flexible drag panels (of various sizes) on the attitude control is assessed. JC2Sat's attitude control system consists of three perpendicular magnetorquers and one reaction/bias-momentum wheel. Four Linear Quadratic Regulator controllers are compared, ranging in complexity from being time-invariant and assuming a rigid satellite, to being periodic and actively suppressing panel vibrations. These include the first controllers which use magnetic attitude control to actively suppress vibrations, and where the periodic vibration suppression controller is able to guarantee asymptotic stability of the linearized system. It was found that for larger panels, the controllers which actively suppressed the vibrations outperformed those that did not.
13

On some aspects of dynamics, modelling, and attitude analysis of satellites

Marandi, Said Rashed January 1988 (has links)
The thesis identifies several limitations in the modelling and attitude stability analysis of two classes of spacecraft: rigid and flexible satellites. Attractive methods are proposed which promise to have far reaching consequences in spacecraft dynamics. These alternatives, developed based on techniques of differential equations, classical mechanics, and differential topology, are indicated below. (a) An Alternate Transition from the Lagrangian of a Satellite to Equations of Motion The classical procedure requires the Lagrangian to be expressed in terms of the corresponding generalized coordinates of the problem. This requirement significantly complicates the derivation of the equations of motion through an introduction of a set of librational generalized coordinates, which is strictly not a part of the dynamical system. Using the Lagrangian in the natural variables (angular velocity, direction cosines, and vibrational coordinates), one develops a procedure for derivation of equations of motion without an a priori choice of rotational generalized coordinates. For the case of a satellite with two flexible plate-type appendages, for example, the approach reduced the formulation time to one-third. (b) Synthesis and Depiction of Rotational Motion of Satellites and Robots The rotational coordinates in use for numerical prediction of orientation of a satellite are either singular or redundant. Furthermore, they lack a convenient visual interpretation. A new set of coordinates is proposed and an associated representation is developed which avoids these limitations. The procedure is applied to represent and integrate numerically the librational response of the flexible satellite mentioned in (a). (c) Resolution of Attitude Stability of Delp Satellites The development here tackles a long outstanding problem in the area of attitude stability of satellites. The resolution of this problem through normalization of the Hamiltonian leads to a better appreciation of stability associated with the class of gravity gradient structures such as the proposed Space Station. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate
14

EXTENDED ORBITAL FLIGHT OF A CUBESAT IN THE LOWER THERMOSPHERE WITH ACTIVE ATTITUDE CONTROL

Moorthy, Ananthalakshmy Krishna 03 July 2019 (has links)
A wide variety of scientifically interesting missions could be enabled by orbital flight altitudes of 150 – 250 km. For the present work, this range of altitudes is defined as extremely Low Earth Orbit (eLEO). The use of low-cost nanosatellites (mass < 10 kg) has reduced the cost barrier to orbital flight over the last decade and the present study investigates the feasibility of using primarily commercial, off-the-shelf (COTS) hardware to build a nanosat specifically to allow extended mission times in eLEO. CubeSats flying in the lower thermosphere have the potential to enable close monitoring of the Earth’s surface for scientific, commercial, and defense-related missions. The results of this research show that the proper selection of primary and attitude control thrusters combined with precise control techniques result in significant extension of the orbital life of a CubeSat in eLEO, thus allowing detailed explorations of the atmosphere. In this study, the orbit maintenance controller is designed to maintain a mission-averaged, mean altitude of 244 km. An estimate is made of the primary disturbance torque due to aerodynamic drag using a high-fidelity calculation of the rarefied gas drag based on a Direct Simulation, Monte-Carlo simulation. The primary propulsion system consists of a pair of electrospray thrusters providing a combined thrust of 0.12 mN at 1 W. Results of a trade study to select the best attitude control option indicate pulsed plasma thrusters operating at 1 W are preferable to reaction wheels or mangetorquers at the selected altitude. An extended Kalman filter is used for orbital position and spacecraft attitude estimations. The attitude determination system consists of sun sensors, magnetometers, gyroscopes serving as attitude sensors. The mission consists of two phases. In Phase I, a 4U CubeSat is deployed from a 414 km orbit and uses the primary propulsion system to deorbit to an initial altitude within the targeted range of 244 +/- 10 km. Phase I lasts 12.73 days with the propulsion system consuming 5.6 g of propellant to deliver a ∆V of 28.12 m/s. In Phase II the mission is maintained until the remaining 25.2 g of propellant is consumed. Phase II lasts for 30.27 days, corresponding to a ∆V of 57.22 m/s with a mean altitude of 244 km. The mean altitude for an individual orbit over the entire mission was found to vary from a maximum of 252 km to a minimum of 236 km. Using this approach, a primary mission life of 30.27 days could be achieved, compared with 3.1 days without primary propulsion.
15

Coupled Attitude And Orbital Control System Using Spacecraft Simulators

Lennox, Scott Evan 16 July 2004 (has links)
Translational and rotational motion are coupled for spacecraft performing formation flying missions. This motion is coupled because orbital control is dependent on the spacecraft attitude for vectored thrust. Formation flying spacecraft have a limited mass and volume for propulsion systems. We want to maximize the efficiency of the spacecraft, which leads to minimizing the error introduced by thrusting in the wrong direction. This thrust direction error leads to the need for a coupled attitude and orbital control strategy. In this thesis a coupled control system is developed using a nonlinear Lyapunov attitude controller and a nonlinear Lyapunov-based orbital controller. A nonlinear Lyapunov attitude controller is presented for a spacecraft with three-axis momentum wheel control. The nonlinear Lyapunov-based orbital controller is combined with a mean motion control strategy to provide a globally asymptotically stable controller. The attitude and orbit control laws are verified separately using numerical simulation, and then are integrated into a coupled control strategy. The coupled system simulations verify that the coupled control strategy is able to correct for an initial relative position error between two spacecraft. / Master of Science
16

Attitude determination for the three-axis spacecraft simulator (TASS) by application of particle filtering techniques

Kassalias, Ioannis 06 1900 (has links)
The accurate determination of spacecraft attitude has always been a critical issue in many applications. The presence of imperfect sensors introduces errors in the system and affects the outcome of the mission. One of the most significant sensors is the rate gyroscope. Particularly, the rate gyros are known to degrade with time, introducing random noise and bias. This calls for estimation algorithms which process the measured data in order to reduce the effects of the disturbances to a minimum. This research presents an approach which takes full advantage on the nonlinear dynamics and possibly non-Gaussian disturbances. It is based on recent work involving particle filters, where the probability density functions are approximated by a relatively large number of parameters. It is shown that accurate attitude estimation can be obtained with a manageable number of particles.
17

Design and simulation of a three-axis stabilized satellite and Kalman filter rate estimator

Vitalich, John 06 1900 (has links)
Approved for public release; distribution is unlimited / Design requirements for a small satellite (NPSAT-1) Attitude Determination and Control Subsystem (ADCS) is a three-axis stabilized spacecraft which requires a control attitude of +/- 1.0 degrees and knowledge attitude of +/- 0.1 degree. Several design aspects are considered in development of attitude control systems for a small satellite, such as: spacecraft dynamics, space environment, disturbance torques, orbit type, and spacecraft complexity. The ideal spacecraft's attitude sensor is a rate gyroscope, which provides rate information to the attitude control system. In the case of NPSAT-1, due to budget constraints alternative sensors will be utilized, such as: a three-axis magnetometer, earth sensors, and a Global Positioning System (GPS). A small satellite designed to have a three-axis stabilized, biased momentum system, must have a robust control system and requires a momentum wheel to provide stiffness to maintain attitude, and magnetic torque rods on each axis. The current design of NPSAT-1 uses all of these sensors to provide rate information for damping and stability to the control system that requires a complicated attitude control design. The purpose of this attitude control design simulation is to investigate and propose a control law utilizing a single pitch momentum wheel and three magnetic torque rods. A further proposal is to utilize a constant speed momentum wheel to avoid momentum damping and over speed, replace the pitch control with magnetic torquers, and develop a Kalman filter estimator to provide all the required angular rates. / Lieutenant Commander, United States Navy
18

Development of a high-precision sensor for the attitude determination of the bifocal spacecraft simulator

Connolly, Brian D. 06 1900 (has links)
Approved for public release; distribution is unlimited / Design Center of the Naval Postgraduate School. The objective of this simulator is to provide on-the-ground simulation of the dynamics and control of spacecraft for high precision Acquisition, Tracking and Pointing applications associated with space based laser relay. The required initial attitude determination accuracy for the Bifocal Relay Mirror test-bed is 10 æ-radians. Normally, in laboratories where very high initial attitude knowledge is required, actual (space qualified) star trackers are incorporated into the testbed design. This is not possible at NPS as the laboratory does not have a skylight to allow visual access to the stars, and the photosensitive nature of many of the experiments would make such an opening inconvenient. Since it is critical to the operation of the testbed to provide accurate attitude knowledge, a substitute system was required. The present thesis documents the development of a new attitude sensor capable of providing attitude information within the required 10æ-radians (within a field of view of the order of 1 deg). The concepts leading up to the final design, the testing and selection of the equipment used in the final configuration, and a detailed explanation of how the final system calibration was performed are discussed in detail. / Lieutenant, United States Navy
19

Orbital aerodynamic attitude control for spacecraft

Hao, Zhou January 2018 (has links)
This dissertation introduces novel techniques for exploiting the environmental aerodynamic forces to actively control the attitude of the spacecraft operating in the lower and middle thermosphere. It includes both simulations and real spacecraft attitude determination and control subsystem development, which provide a complete picture of the application of the aerodynamic forces to benefit space missions that are operating very close to Earth, as well as contribute to the knowledge of rarefied gas aerodynamics in the lower and middle part of the thermosphere. The research starts by reviewing the current progress of thermosphere science and rarefied gas aerodynamics to construct a high fidelity aerodynamic model for spacecraft operating in the rarefied gas (mainly atomic oxygen) environment in very low Earth orbits (below 450 km) and following by a brief system level analysis of the benefits and challenges for the spacecraft flying lower to Earth. A real spacecraft is also developed to validate of the application of the aerodynamic forces for attitude control. The aspect of the design included in this dissertation focuses mainly on the attitude determination and control system development of satellite. The CubeSat has a generic design with deployable solar panels that can be rotated to control the aerodynamic torques. Based on the common attitude control requirements of spacecraft operating in very low Earth orbits, and the hardware capability of the satellite three novel orbital aerodynamic attitude control strategies are proposed: Energy Optimized B-dot Detumbling into an Aerostable State; Active Orbital Aerodynamic Coarse Pitch/Yaw Control; a 3-axis Orbital Aerodynamic Torques Adaptive Sliding Mode Control. The control performance for each control algorithm is validated numerically in high-fidelity attitude propagators. Knowledge of the thermospheric winds is important as they influence the control performance and the dynamic response of the spacecraft, aerostable designs steering into the thermosphere wind vector. Two novel computational methods to measure the thermospheric wind from the dynamic response of the spacecraft due to aerodynamic forces are proposed. The in-situ measured wind vector benefits the attitude observation in the feedback control systems, which helps to improve the adapting performance and to increase the control accuracy. The proposed novel aerodynamic attitude control algorithms can be adapted for similar spacecraft operating in the very low Earth orbits with modifications to the deployable solar panels or adding movable aerodynamic control surfaces. In addition, this proposed orbital aerodynamic attitude control system works not only in the very low Earth orbits but can also be potentially implemented for spacecraft operating in the rarefied gas region of the atmospheres of other planets.
20

High Performance Attitude Determination and Control for Nanosatellite Missions

Johnston-Lemke, Bryan 08 December 2011 (has links)
Small satellites are growing in popularity because they offer an effective option that enables missions otherwise too schedule or cost limited. However, many possible missions require improved platform capabilities without sacrificing the cost effective nature of small satellites before they become viable. Described is the development and validation of high performance attitude determination and control for nanosatellite missions. Considered are astronomy missions, requiring very fine pointing stability, and formation flying missions requiring rapid manoeuvring while maintaining antenna coverage towards secondary pointing targets. It will be shown that power and volume limited nanosatellites are capable of this level of attitude performance by leveraging the techniques normally reserved for larger spacecraft. Discussed are attitude state estimation techniques and control laws developed for the BRITE stellar photometry constellation and CanX-4 and CanX-5 formation flying mission, along with the challenges associated with implementing and validating these designs for real space missions.

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