Browsing by Subject "CubeSat"
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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 CubeSat autonomous rendezvous and docking software(2014-12) Fear, Andrew John; Lightsey, E. GlennAn autonomous mission manager is being developed for use on CubeSats to perform proximity operations with other vehicles. The mission manager software is designed to run in real-time on a microprocessor used on a CubeSat. A simulation tool was developed that provides orbital dynamics and sensor measurements to test the mission manager software. A scenario was developed to demonstrate the control of a spacecraft from 1 km to 1 m to a target vehicle. Two small satellites were simulated in near-circular orbits around Earth at an approximate 400 km altitude. Each satellite is incorporated with simulated sensors and a Kalman filter. The simulation tool includes models for accelerometers and Global Positioning System receivers. Noise corruption is added to the modeled sensors to simulate imperfect knowledge. The simulation environment is capable of modeling Earth as a spherical or non-spherical body with spherical gravitational harmonics. Simulation parameters, such as the vehicle's initial states, Earth gravity model, and sensor noise are easily changed without recompiling the program through a simulation input file.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 Magnetic control for spinning 3-unit science CubeSat(2014-12) McDonald, Karl JosephA control system is designed and validated for a 3-unit CubeSat science mission. Utilizing three magnetorquers and one reaction wheel the system achieves a 6 rotation per minute spin rate and orbit normal pointing vector of the long axis of a 3-unit CubeSat. The design is validated across an evolution of scenarios, from idealized to flight-like with expected bias and noise terms added in. Estimated mass imbalances and the limitations of the power system driving the magnetorquers force the final system design to use only magnetorquers. Considerations are also taken for the science instrument to limit the interference of magnetorquers. The overall satellite design and software implementation are also briefly discussed.Item Magnetic control for spinning 3-unit science CubeSat(2014-12) McDonald, Karl Joseph; Lightsey, E. GlennA control system is designed and validated for a 3-unit CubeSat science mission. Utilizing three magnetorquers and one reaction wheel the system achieves a 6 rotation per minute spin rate and orbit normal pointing vector of the long axis of a 3-unit CubeSat. The design is validated across an evolution of scenarios, from idealized to flight-like with expected bias and noise terms added in. Estimated mass imbalances and the limitations of the power system driving the magnetorquers force the final system design to use only magnetorquers. Considerations are also taken for the science instrument to limit the interference of magnetorquers. The overall satellite design and software implementation are also briefly discussed.Item The metrics of spacecraft design reusability and cost analysis as applied to CubeSats(2012-05) Brumbaugh, Katharine Mary; Lightsey, E. Glenn; Guerra, LisaThe University of Texas at Austin (UT-Austin) Satellite Design Lab (SDL) is currently designing two 3U CubeSat spacecraft – Bevo-2 and ARMADILLO – which serve as the foundation for the design reusability and cost analysis of this thesis. The thesis explores the reasons why a small satellite would want to incorporate a reusable design and the processes needed in order for this reusable design to be implemented for future projects. Design and process reusability reduces the total cost of the spacecraft, as future projects need only alter the components or documents necessary in order to create a new mission. The thesis also details a grassroots approach to determining the total cost of a 3U CubeSat satellite development project and highlights the costs which may be considered non-recurring and recurring in order to show the financial benefit of reusability. The thesis then compares these results to typical models used for cost analysis in industry applications. The cost analysis determines that there is a crucial gap in the cost estimating of nanosatellites which may be seen by comparing two widely-used cost models, the Small Satellite Cost Model (SSCM <100 kg) and the NASA/Air Force Cost Model (NAFCOM), as they apply to a 3U CubeSat project. While each of these models provides a basic understanding of the elements which go into cost estimating, the Cost Estimating Relationships (CERs) do not have enough historical data of picosatellites and nanosatellites (<50 kg) to accurately reflect mission costs. Thus, the thesis documents a discrepancy between widely used industry spacecraft cost models and the needs of the picosatellite and nanosatellite community, specifically universities, to accurately predict their mission costs. It is recommended to develop a nanosatellite/CubeSat cost model with which university and industry developers alike can determine their mission costs during the designing, building and operational stages. Because cost models require the use of many missions to form a database, it is important to start this process now at the beginning of the nanosatellite/CubeSat boom.Item A reusable command and data handling system for university CubeSat missions(2013-12) Johl, Shaina Ashley Mattu; Lightsey, E. GlennA Command and Data Handling (C&DH) system is being developed as part of a series of CubeSat missions being built at The University of Texas at Austin’s Texas Spacecraft Laboratory (TSL). With concurrent development of four missions, and with more missions planned for the future, the C&DH team is developing a system architecture that can support many mission requirements. The presented research aims to establish itself as a reference for the development of the C&DH system architecture so that it can be reused for future university missions. The C&DH system is designed using a centralized architecture with one main flight computer controlling the actions and the state of the satellite. A Commercial Off-The-Shelf (COTS) system-on-module embedded computer running a Linux environment hosted on a custom interface board is used as the platform for the mission software. This design choice and the implementation details of the flight software are described in detail in this report. The design of the flight software and the associated hardware are integral components of the spacecraft for the current missions in the TSL which, when flown, will be some of the most operationally complex CubeSat missions attempted to date.Item Single station Doppler tracking for satellite orbit prediction and propagation(2015-05) Dykstra, Matthew C.; Fowler, Wallace T.; Lightsey, E. GlennPresently, there are two main methods of launching a cube satellite into Earth orbit. The first method is to purchase a secondary payload slot on a major launch vehicle. For the second method, the satellite must first be transported via a major launch vehicle to the International Space Station. From there, the satellite is loaded into one of two deployment mechanisms, and deployed at a specified time. In each case, the satellite's initial orbit is not accurately known. For ground operators this poses a problem of position uncertainty. In order to solve this problem, a satellite tracking algorithm was developed to use an initial two-line element set for coarse orbit prediction, followed by Doppler measurements for continuous processing and updating. The system was tested using simulated data. The analysis showed that this low-cost, scalable system will satisfy the tracking requirements of many cube satellite missions, including current missions at the University of Texas.Item A software tool suite for small satellite risk management(2015-05) Gamble, Katharine Brumbaugh; Fowler, Wallace T.Risk management plans improve the likelihood of mission success by identifying potential failures early and planning mitigation methods to circumvent any issues. However, in the aerospace industry to date, risk management plans have typically only been used for larger and more expensive satellites, and have rarely been applied to satellites in the shape of 10 x 10 x 10 centimeter cubes, called CubeSats. Furthermore, existing risk management plans typically require experienced personnel and significant time to run the analysis. The purpose of this research was to develop two risk management software tools, the CubeSat Risk Analysis tool and the CubeSat Decision Advisor tool, which could be used by anyone with any level of experience. Moreover, the tools simply require the user to enter their mission-specific data; the software tools calculate the required analysis. The CubeSat Risk Analysis tool was developed for the purpose of reducing the subjectivity associated with estimating the likelihood and consequence of spacecraft mission risks. The tool estimates mission risk in terms of input characteristics, such as satellite form factor, mass, and development cycle. Using a historical database of small satellite missions, which was gathered in the course of this research, the software determines the mission risk root causes which are of the highest concern for the given mission. The CubeSat Decision Advisor tool uses components of decision theory such as decision trees, multi-attribute utility theory, and utility elicitation methods to determine the expected utility of a mitigation technique alternative. Based on the user’s value preference system, assessment of success probabilities, and resources required for a given mitigation technique, the tool suggests the course of action which will normatively yield the most value for the cost, personnel, and time resources required. The goals of this research were met in the development of two easily-accessible and free risk management software tools to assist in university satellite mission development. But more importantly, these tools will reach beyond the academic setting and allow small satellites to continue to evolve as a platform to accomplish educational, scientific, and military objectives.Item A star tracker design for CubeSats(2012-05) McBryde, Christopher Ryan; Lightsey, E. Glenn; D'Souza, ChristopherThis research outlines a low-cost, low-power, arc-minute accurate star tracker that is designed for use on a CubeSat. The device is being developed at the University of Texas at Austin for use on two different 3-unit CubeSat missions. The hardware consists of commercial off-the-shelf parts designed for use in industrial machine vision systems and employs a 1024x768 grey-scale charge coupled device (CCD) sensor. The software includes the three standard steps in star tracking: centroiding, star identification, and attitude determination. Centroiding algorithms were developed in-house. The star identification code was adapted from the voting method developed by Kolomenkin, et al. Attitude determination was performed using Markley's singular value decomposition method. The star tracker was then tested with internal simulated star-fields. The resulting accuracy was less than an arcminute. It was concluded that this system is a viable option for CubeSats looking to improve their attitude determination. On-orbit demonstration of the system is planned when the star tracker flies on the planned CubeSat missions in 2013 or later. Further testing with external simulated star fields and night sky tests are also planned.