Browsing by Subject "Guidance"
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Item A homotopic approach to solve the fuel optimal spacecraft proximity operations problem(2017-05) Gulino, Marco; Akella, Maruthi Ram, 1972-This report focuses on finding the low-thrust fuel optimal solution to a class of spacecraft proximity operations subject to path constraints. The mission is for a service spacecraft to perform a surveying orbit relative to a reference within a prescribed period, without violating a no fly zone represented by a sphere centered on the reference vehicle. Clohessy-Wiltshire equations are used, together with the controllability Gramian of the resulting linear system, to obtain an analytical solution to the energy optimal problem. A homotopic approach is subsequently shown to serve as an effective bridge from the energy optimal solution toward the fuel optimal solution.Item Analysis and order reduction of an autonomous lunar lander navigation system(2009-08) Newman, Clark Patrick; Bishop, Robert H., 1957-; Akella, Maruthi R.A navigation system for precision lunar descent and landing is presented and analyzed. The navigation algorithm is based upon the extended Kalman Filter and employs measurements from an inertial measurement unit to propagate the vehicle position, velocity, and attitude forward in time. External measurements from an altimeter, star camera, terrain camera, and velocimeter are utilized in state estimate updates. The navigation algorithm also attempts to estimate the values of uncertain parameters associated with the sensors. The navigation algorithm also estimates the map-tie angle of the landing site which is a measure of the misalignment of the actual landing site location on the surface of the Moon versus the estimated position of the landing site. The navigation algorithm is subject to a sensitivity analysis which investigates the contribution of each error source to the total estimation performance of the navigation system. Per the results of the sensitivity analysis, it is found that certain error sources need not be actively estimated to achieve similar estimation performance at a reduced computational burden. A new, reduced-order system is presented and tested through covariance analysis and a monte carlo analysis. The new system is shown to have comparable estimation performance at a fraction of the computer run-time, making it more suitable for a real-time implementation.Item An attitude determination and control system for small satellites(2015-05) Tam, Margaret Hoi Ting; Fowler, Wallace T.; Lightsey, E. GlennA flexible, robust attitude determination and control (ADC) system is presented for small satellite platforms. Using commercial-off-the-shelf sensors, reaction wheels, and magnetorquers which fit within the 3U CubeSat form factor, the system delivers arc-minute pointing precision. The ADC system includes a multiplicative extended Kalman filter for attitude determination and a slew rate controller that acquires a view of the Sun for navigation purposes. A pointing system is developed that includes a choice of two pointing controllers -- a proportional derivative controller and a nonlinear sliding mode controller. This system can reorient the spacecraft to satisfy a variety of mission objectives, but it does not enforce attitude constraints. A constrained attitude guidance system that can enforce an arbitrary set of attitude constraints is then proposed as an improvement upon the unconstrained pointing system. The momentum stored by the reaction wheels is managed using magnetorquers to prevent wheel saturation. The system was thoroughly tested in realistic software- and hardware-in-the-loop simulations that included environmental disturbances, parameter uncertainty, actuator dynamics, and sensor bias and noise.Item Computationally efficient algorithms for spacecraft relative navigation and rendezvous(2023-08-02) Kaki, Siddarth Bhargava; Akella, Maruthi Ram, 1972-; Jones, Brandon; Zanetti, Renato; Russell, Ryan; D’Souza, ChristopherThere is tremendous interest in the development of spacecraft guidance, navigation, and control technologies that enable on-orbit servicing, assembly, and manufacturing missions with limited human supervisory support. These applications provide strong motivations for the design of computationally lightweight algorithms that enable autonomous operations, especially for missions constrained by size, weight, power, and cost (SWaP-C) such as cubesats. However, the more democratic access to space has also further contributed to the space debris problem, with worryingly many defunct and derelict spacecraft crowding up precious space. Dealing with such noncooperative objects poses significant challenges, with large uncertainties in mass properties and applied forces by the environment. This dissertation addresses such problems related to SWaP-C constraints and also noncooperative targets within the fields of relative spacecraft navigation and rendezvous. The first topic addresses relative angular velocity and associated uncertainty estimation from a geometrical perspective via batch processes. The second topic addresses real-time relative pose estimation and tracking using monocular imagery for cubesat applications. The third topic addresses analytical guidance solutions for radial-thrust-based far-field rendezvous and orbit rotations. Finally, the fourth topic addresses semi-analytical techniques to achieve circular orbit changes with radial and velocity-normal thrust.Item A critical evaluation of modern low-thrust, feedback-driven spacecraft control laws(2012-12) Hatten, Noble Ariel; Ocampo, Cesar; Akella, MaruthiLow-thrust spacecraft trajectory optimization is often a difficult and time-consuming process. One alternative is to instead use a closed-loop, feedback-driven control law, which calculates the control using knowledge of only the current state and target state, and does not require the solution of a nonlinear optimization problem or system of nonlinear equations. Though generally suboptimal, such control laws are attractive because of the ease and speed with which they may be implemented and used to calculate feasible low-thrust maneuvers. This thesis presents the theoretical foundations for seven modern low-thrust control laws based on control law "blending" and Lyapunov control theory for a particle spacecraft operating in an inverse-square gravitational field. The control laws are evaluated critically to determine those that present the best combinations of thoroughness of method and minimization of user input required. The three control laws judged to exhibit the most favorable characteristics are then compared quantitatively through three numerical simulations. The simulations demonstrate the effectiveness of feedback-driven control laws, but also reveal several situations in which the control laws may perform poorly or break down altogether due to either theoretical shortcomings or numerical difficulties. The causes and effects of these issues are explained, and methods of handling them are proposed, implemented, and evaluated. Various opportunities for further work in the area are also described.Item Design of a CubeSat guidance, navigation, and control module(2011-08) Kjellberg, Henri Christian; Lightsey, E. Glenn.; Fowler, Wallace T.A guidance, navigation, and control (GN&C) module is being designed and fabricated as part of a series of CubeSats being built by the Satellite Design Laboratory at the University of Texas. A spacecraft attitude control simulation environment called StarBox was created in order to perform trade studies and conduct performance analysis for the GN&C module. Navigation and control algorithms were tested using StarBox and then implemented onto an embedded flight computer. These algorithms were then tested in a hardware-in-the-loop simulation. In addition, the feasibility of utilizing advanced constrained attitude control algorithms was investigated by focusing on implementation in flight software. A mechanical and electrical design for the GN&C module was completed. A prototype system was set up on a bench-top for integrated testing. The analysis indicates that the system will satisfy the requirements of several CubeSat missions, including the current missions at the University of Texas known as Bevo2 and ARMADILLO.Item Love, guidance, and parental relationships : protective factors and barriers identified by youth living the school-to-prison pipeline(2019-05) Hermosura, Lorna Mae N.; Valenzuela, Angela; Somers, Patricia (Patricia A.); Green, Terrance L.; Crosnoe, Robert; Davis, King E.Studies on risk and protective factors for juvenile incarceration rarely include the perspectives of youth who are directly effected. This research is an analysis of 325 essays written by youth who are living the school-to-prison pipeline. Of the participants (ages 13 to 17), nearly half (46%) were incarcerated, 11% were "inside the pipeline," as they were truant or known by the police, and the remaining 43% were identified as "at-risk" due to their location in a high crime neighborhood or their voluntarily attendance at an alternative high school. The youth essays were in response to the prompt known as the IF Question: If there was something that someone could have said or done to help you, what would it be? Data were collected during structured workshops facilitated by trained workshop facilitators from The IF Project, who were also formerly incarcerated. The essays yielded 614 coded excerpts revealing risk and protective factors identified by youth living the school-to-prison pipeline while highlighting their high level of self-awareness. Despite some variance between the three groups, the overall findings reveal that youth most frequently identified love followed by guidance as protective factors. Youth also identified difficult life circumstances as barriers to their progress with parental relationships being the most frequent barrier cited across all three groups of youth within the sample. Implications and recommendations for those working to intervene or prevent juvenile incarceration include: ensuring intentionality regarding the quality of interaction between staff and participants; increasing opportunities for youth to build internal resources such as self-esteem and coping skills; preparing youth for independence and self-sufficiency given their difficult life circumstances; ensuring those who are truant and otherwise inside the pipeline have access to academic supports; and providing bias training to decision-makers that provide a historical context for the persistent state of disproportionate social outcomes among people of color and those from impoverished backgrounds.Item A self-contained guidance and targeting algorithm for spacecraft applications(2012-08) Scarritt, Sara Kathryn; Marchand, Belinda G.; Hull, David G.; Ocampo, Cesar A.; D'Souza, Christopher; Weeks, Michael W.The development of a self-contained, onboard, fully autonomous trajectory guidance tool for spacecraft is presented. To be considered completely autonomous requires the capability to both identify an appropriate startup solution, and then use that solution to target a set of user-defined path and endpoint constraints. To minimize the cost of flight software development and validation, both the generation of the startup solution and the targeting algorithm are designed to be as computationally efficient as possible. This study addresses both the determination of a startup arc and the subsequent targeting process. The first part of the investigation considers the targeting algorithm. Linear targeting through differential corrections is a well-known approach for identifying feasible solutions that meet specified mission and trajectory constraints. However, to date, these methods relied on the assumption that the associated control inputs were impulsive in nature. This research focuses on the theoretical development and numerical validation of a generalized linear targeting algorithm capable of accommodating finite periods of continuous control action for a wide range of applications. Examples are presented to illustrate the general concept and to contrast the performance of this new targeting process against more classical impulsive targeting methods. The second section of the study introduces a novel approach utilizing artificial potential function methods to identify suitable startup solutions. Although common in other types of path planning, these methods have not yet been used for orbital or interplanetary trajectory design, primarily due to their inherent suboptimality. However, results show that this issue can be addressed with relative ease by the targeting algorithm.Item Systems engineering processes for a student-based design laboratory(2009-12) Garner, Michael Dax; Bishop, Robert H., 1957-; Guerra, Lisa A.A student-based university environment for engineering design and development is much different from a product development environment within the aerospace industry. Therefore, a different approach to systems engineering should be considered. By its very nature, a university product development laboratory thrives on creativity and rejects bureaucracy. Experience shows that continuity and discipline within a project is crucial for success. The practice of systems engineering enables technical project discipline. Systems engineering is the art and science of developing an operable system that meets requirements within imposed constraints. The purpose of this thesis is to describe the systems engineering processes and techniques necessary for a student-based project, and explicitly show how to implement these processes. Although attempts have been made to utilize a few systems engineering techniques in past projects, many students did not properly and consistently apply those techniques to the technical design work. The goal of the thesis is to tailor the NASA systems engineering processes to a student-based design laboratory environment and to apply the methodologies to the mission design of Paradox. The Picosatellite for Autonomous Rendezvous and Docking on-Orbit eXperiment, or Paradox, is the second of four missions to demonstrate autonomous rendezvous and docking with a picosatellite-class satellite. A strong technical contribution highlighted within the thesis involves developing an open architecture rendezvous targeting algorithm for the Paradox mission in the face of large mission architecture uncertainties. The robust targeting algorithm builds from previous work utilizing an optimizer based on the Clohessey-Wiltshire equations and an iterative Lambert targeter. The contribution extends the rendezvous transfer times by including a multi-revolution Lambert targeter. The rendezvous algorithm will perform successfully given any launch vehicle and target spacecraft vehicle supporting the notion of an open architecture to satisfy the mission. The development of the algorithm is embedded within the context of the systems engineering processes to clearly showcase the intimate connection between systems engineering processes and the technical engineering design of a mission.