Browsing by Subject "Attitude Determination"
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Item Characterizing Performance and Errors of Coarse Sun Sensors(2017-12) Saborio, Ricardo JThis presentation focuses on outlining the experimental setup and results for the characterization of Coarse Sun Sensor performance for in-orbit attitude determination in small satellites. Coarse Sun Sensors provide an inexpensive alternative to the more commonly used Fine Sun Sensors in the aerospace industry. These sensors are a fraction of the cost ($1.50 vs $3500 per unit) of the space grade sun sensors in regular satellites and, based on the results obtained in this work, the sensors themselves prove to be relatively effective at measuring the incoming sun vector. The work done in this Undergraduate Research Opportunity (UROP) is intended to serve as a stepping-stone for the development of an inexpensive sun-sensor packet for the University of Minnesota small satellite research group’s payloads. These payloads require accurate pointing at the sun while in orbit and thus such a sensor packet would be key to mission success.Item Methods for enhancing carrier phase GNSS positioning and attitude determination performance.(2010-05) Zheng, GuijinThis thesis explores the methods for enhancing the performance of using low cost, single frequency Carrier phase Differential Global Navigation Satellite System (CDGNSS) in real-time, safety or liability critical applications. This is done by improving the integer ambiguity resolution performance and carrier phase error modeling. CDGNSS is considered for a broad range of real-time applications which require both a high precision relative positioning and attitude determination system. This is because of the drift-free nature of the GNSS measurement errors and the precise nature of the carrier phase measurement. The key to making full use of the precise nature of the carrier phase measurement is to fix the integer ambiguity quickly and reliably. This poses the biggest challenge for a low cost single frequency system. For the attitude determination problem, the precisely known baseline lengths can be used to improve the integer ambiguity resolution performance. Traditionally, the relative positioning problem was solved independently of the attitude determination problem and, thus could not leverage the precisely known baseline lengths of the attitude determination system. However, by integrating the two systems together, the precisely known baseline lengths can be used to improve the relative positioning system as well. The first part of the thesis develops an integration framework to improve the integer ambiguity resolution performance for the relative positioning system and the attitude determination system simultaneously. The second part of the thesis provides a GNSS antenna Phase Center Variation (PCV) error model development to improve the accuracy of the integrated system. It also examines the feasibility analysis of using the developed error model for a real-time dynamic application. The challenging of using this in the real time lies in the fact that PCV error magnitude is small (less than 2cm) and the developed error model is a function of unknown parameter such as attitude. A feasibility analysis of the developed model with a set of specific antennas is performed and assessed.Item Real Time Angle Of Attack Estimation For The Hycube Flight Vehicle In Gps-Denied Re-Entry(2024-01) Vedvik, SophiaWith global interests in the study of hypersonic flow, large research efforts have gone towards collecting statistically significant amounts of high speed flow data at low costs. CubeSats are proving to be an economical testing platform for a variety of scientific experiments, where valuable hypersonic data can be collected and relayed upon re-entry to Earth. However, due to the budget, volume, and power constraints of CubeSats, many of the on-board sensors, including inertial measurement units (IMUS), have decreased accuracy. For purposeful data collection to occur, the sensors on-board typically work in conjunction with robust synthetic air data algorithms. To back out useful data on the vehicle's response during re-entry, the angle of attack of the vehicle must be estimated with one of such algorithms. This work proposes using an Extended Kalman Filter (EKF) which fuses an attitude determination algorithm with low-grade IMU angular rates and measurements of Earth's magnetic field. But in the case of re-entry, the vehicle will become deprived of Global Positioning System (GPS) data, which is required to obtain estimates of the Earth's magnetic field that work in conjunction with magnetometer magnetic field measurements. Thus, after developing the EKF framework, this work will perform a trade study to analyze ways in which Earth's magnetic field can still be a viable method to aid low-grade IMU attitude estimates. The trade study environment is modeled after the Hypersonic Configurable Unit Ballistic Experiment (HyCUBE), a project in development at the University of Minnesota that is leveraging the CubeSat form factors to collect valuable hypersonic flow data upon re-entry. Future work and improvements to the EKF, as well as the impact of this work will then be discussed.Item Single-Vector Aiding of an IMU for CubeSat Attitude Determination(2020-07) Laughlin, KailThis thesis examines CubeSat attitude determination using the Earth’s magnetic field (EMF) vector aiding a low-cost IMU. CubeSats provide relatively cost-effective methods of performing scientific research in orbital environments. However, to adequately perform this research, knowledge of the CubeSat’s orientation in 3D space (attitude) is often required. To that end, the design of a reliable attitude determination (AD) system on-board a CubeSat is a critical aspect for many mission designers. As a primary goal of CubeSat design is to ensure science objectives are met while minimizing, cost, mass, and volume, this thesis investigates a minimal sensor approach to CubeSat AD. Specifically, an inertial based AD scheme reliant on the use of an inertial measurement unit (IMU) aided only by vector measurements of the Earth’s magnetic field (EMF) is developed. An extended Kalman filter (EKF) approach to recursively estimate the attitude on-orbit using an IMU and a three-axis magnetometer (TAM) is detailed. Additionally, we describe a test to assess the stochastic observability of the EKF developed. We present simulation results showcasing the performance of the AD system for multiple orbital inclinations and initial attitude errors. Moreover, we discuss conditions in which the EMF vector can and cannot be effectively utilized as the sole aiding measurement, and we evaluate the stochastic observability of the linearized discrete time system. We extend the AD system discussed here to two current University of Minnesota Small Satellite Research Lab CubeSat designs: IMPRESS and EXACT. We describe future work for the implementation of the AD system and potential improvements to the EKF design.