Browsing by Subject "Satellite"
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Item Analytical approach to the design of optimal satellite constellations for space-based space situational awareness applications(2011-12) Biria, Ashley Darius; Marchand, Belinda G.; Lightsey, E. GlennIn recent years, the accumulation of space debris has become an increasingly pressing issue, and adequately monitoring it is a formidable task for designated ground-based sensors. Supplementing the capabilities of these ground-based networks with orbiting sensing platforms would dramatically enhance the ability of such systems to detect, track, identify, and characterize resident space objects -- the primary goals of modern space situational awareness (SSA). Space-based space situational awareness (SBSSA), then, is concerned with achieving the stated SSA goals through coordinated orbiting sensing platforms. To facilitate the design of satellite constellations that promote SSA goals, an optimization approach is selected, which inherently requires a pre-defined mathematical representation of a cost index or measure of merit. Such representations are often analytically available, but when considering optimal constellation design for SBSSA applications, a closed-form expression for the cost index is only available under certain assumptions. The present study focuses on a subset of cases that admit exact representations. In this case, geometrical arguments are employed to establish an analytical formulation for the coverage area provided as well as for the coverage multiplicity. These analytical results are essential in validating numerical approximations that are able to simulate more complex configurations.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 Development and testing of a miniaturized, dual-frequency, software-defined gps receiver for space applications(2011-12) Joplin, Andrew Jonathan; Lightsey, E. Glenn; Humphreys, ToddWhile dual-frequency GPS receivers have been used in space for more than two decades, the size, power, and cost of this technology is an important driver for future space missions. The growing availability of launch opportunities for very small satellites known as nanosatellites and CubeSats raises the possibility of more affordable access to space measurements if the observation quality is sufficient to support the user's needs. This thesis presents the initial development and testing of the Fast, Orbital, TEC, Observables, and Navigation (FOTON) receiver: a small, reconfigurable, dual-frequency, space-based GPS receiver. Originally developed as a science-grade software receiver for monitoring ionospheric scintillation and total electron content (TEC), this receiver was designed to provide high-quality GPS signal observations. The original receiver hardware was miniaturized and the software has been adapted for low earth orbit (LEO) operations. FOTON now fits within a 0.5U CubeSat form factor (8.3 x 9.6 x 3.8 cm), weighs 326 g, and consumes 4.5 W of instantaneous power, which can be reduced to <1 W orbit average power with on-off duty cycling. The receiver has been designed with commercial parts to keep manufacturing costs low. Significant testing of FOTON has been performed with live signals and with signals generated by a Spirent GPS signal simulator. Initial terrestrial tests demonstrate behavioral consistency with the original heritage high-performance receiver. Several LEO simulations are presented, demonstrating FOTON's single-frequency and dual-frequency-enhanced positioning down to 0.5 m and 1.5 m, respectively, which can be improved using Kalman filter based POD. FOTON's potential for GPS radio occultation observation is also demonstrated. In addition, its acquisition and reacquisition performance is presented; on average, FOTON's time to first fix is approximately 45 seconds. Finally, navigation in geostationary orbit (GEO), a challenging application for space-based GPS receivers, is demonstrated. Extensive testing demonstrates that FOTON is a robust, versatile, high-precision dual-frequency space receiver. Its low cost, size, weight, and power requirements are key enablers for future small-satellite missions.Item G.R.A.C.E. satellite thermal model(2012-12) Jones, Fraser Black III; Howell, John R.I developed a thermal model of the Gravity Recovery and Climate Experiment satellite for the Center for Space Research to use in verifying their thermal models and for developing the next generation of satellites for their experiments. I chose COMSOL to model the satellite and used ProEngineer and 3Ds Max to generate the mesh from a .STEP file provided by DaimlerChrysler. I adjusted the model based on previous computer models and actual telemetry data from the GRACE satellite provided from 2002 through 2008. Using the model, I developed a sensitivity analysis of the satellites key thermal environment components and used that to recommend design changed for the next generation of satellites. Special attention should be given to redesigning the Star Camera Arrays and the heat transfer between the Main Equipment Platform and the Radiator.Item Measuring liquefaction-induced deformation from optical satellite imagery(2014-05) Martin, Jonathan Grant; Rathje, Ellen M.Liquefaction-induced deformations associated with lateral spreading represent a significant hazard that can cause substantial damage during earthquakes. The ability to accurately predict lateral-spreading displacement is hampered by a lack of field data from previous earthquakes. Remote sensing via optical image correlation can fill this gap and provide data regarding liquefaction-induced lateral spreading displacements. In this thesis, deformations from three earthquakes (2010 Darfield, February 2011 Christchurch, and 2011 Tohoku Earthquakes) are measured using optical image correlation applied to 0.5-m resolution satellite imagery. The resulting deformations from optical image correlation are compared to the geologic conditions, as well as field observations and measurements of liquefaction. Measurements from optical image correlation are found to have a precision within 0.40 m in all three cases, and results agree well with field measurements.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 Mission planning tool for small satellites(2013-12) Mathieu, Perrine; Lightsey, E. GlennThe Texas Spacecraft Laboratory (TSL) at the University of Texas at Austin is currently planning to launch two CubeSat missions in 2014. Innovations are more readily attempted on such low-risk small satellites than with higher-cost payloads, which puts CubeSats at the forefront of space research. The TSL CubeSats will thus be used to pioneer and demonstrate new on-orbit technology. Due to the innovative aspect of the CubeSat missions, limited prior experience exists with the technology used. It is thus important to have an accurate understanding of mission operations prior to launch through computer simulation. In order to improve the success and reliability of current and future TSL missions, a MATLAB tool was developed to simulate on-orbit operations. The various capabilities of the user-friendly tool developed include power budget calculations, pass determination and orbit simulation. The comprehensive program can predict the life of the spacecraft at critical moments of its operation and, in general, help improve understanding of how to successfully meet mission requirements and design mission operations.Item Numerical analysis and design of satellite constellations for above the horizon coverage(2010-12) Takano, Andrew Takeshi; Marchand, Belinda G.; Fowler, Wallace T.As near-Earth space becomes increasingly crowded with spacecraft and debris, the need for improved space situational awareness has become paramount. Contemporary ground-based systems are limited in the detection of very small or dim targets. In contrast, space-based systems, above most atmospheric interference, can achieve significant improvements in dim target detection by observing targets against a clutter-free space background, i.e. targets above the horizon (ATH). In this study, numerical methods for the evaluation of ATH coverage provided by constellations of satellites are developed. Analysis of ATH coverage volume is reduced to a planar analysis of cross-sectional coverage area in the orbit plane. The coverage model performs sequences of boolean operations between polygons representing cross-sections of satellite sensor coverage regions and regions of interest, returning the coverage area at the desired multiplicity. This methodology allows investigation of any coverage multiplicity for planar constellations of any size, and use of arbitrary sensor profiles and regions of interest. The implementation is applied to several constellation design problems demonstrating the utility of the numerical ATH coverage model in a constellation design process.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 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.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.