Browsing by Subject "Small satellites"
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Item Design and testing of a 3D printed propulsion system for small satellites(2015-05) Stevenson, Terry Hurley; Fowler, Wallace T.; Lightsey, E. GlennA cold gas propulsion system for small spacecraft orbital maneuvers was developed by the University of Texas at Austin's Texas Spacecraft Laboratory. The thruster will allow the Prox-1 spacecraft, developed by the Georgia Institute of Technology, to conduct small scale maneuvers in Earth orbit. 3D printing was used to create a geometrically complex design at a low cost, and allowed the thruster to make efficient use of the available volume. The system was equipped with an onboard microcontroller that provides precise timing for firings, and can collect data from various sensors to send to the flight computer. The testing of this thruster focused on determining the level of thrust available and the specific impulse of the system. The thrust was found to be considerably higher during short pulses (2 milliseconds) than during long pulses (10 milliseconds), from 50±16 mN to 35±2.4 mN, respectively. The specific impulse was found to be 55.4±17.7 seconds, which is sufficient to provide the Prox-1 thruster with a required velocity change of 15 m/s. A testing unit of the thruster was assembled and delivered in January of 2015, and the flight unit is scheduled for delivery in summer of 2015.Item Examining differential drag control in a full system simulation(2011-12) Lum, Annie Megan; Lightsey, E. Glenn; Ocampo, CesarDifferential drag controllers have been examined in the context of a full system simulation of a target/chaser pair of spacecraft in low Earth orbit. An Extended Kalman Filter has been designed to process measurement sets from GPS receivers on the target and chaser spacecraft. The estimated state from the Kalman Filter is used in a differential drag control algorithm to determine the appropriate control action. Modifications are made to the standard differential drag control algorithms to reduce unnecessary actuations in the presence of errors in the dynamic modeling, control actuation, and incoming measurements. Detailed explanations of the algorithms, dynamic models, and derivations for both the Kalman Filter and the differential drag control laws are presented. Multiple test cases are used to validate the controller performance under a variety of initial conditions. In these simulations, the differential drag control algorithms successfully maneuver the chaser spacecraft from the initial conditions to a final state with instantaneous time-average position (relative to the target spacecraft) of not more than 10 meters in the radial and in-track directions. Modifications to the standard control algorithms ensure that extraneous control actuations are minimized. An optimization algorithm is used determine the time-optimal differential drag control history, and the results are compared to the standard control logic and modified control logic. Based on the optimization results, it is recommended that a system employing differential drag control (especially those with limited computational resources) should use the modified control logic, as it provides a standardized methodology that can be followed in any mission.Item Small Satellite Applications of Commercial off the Shelf Radio Frequency Integrated Circuits(2012-02-14) Graves, JohnWithin the first decade of the 21st century, the aerospace community has seen many more opportunities to launch small spacecraft in the 10 to 100 kg mass class. Coupled with this has been consistent interest from the government in developing small-spacecraft platforms to expand civil and military mission possibilities. Small spacecraft have also given small organizations such as universities an increased access to space. Because small satellites are limited in size, power, and mass, new and often nontraditional capabilities must be explored and developed to make them viable and attractive when compared with larger and more proven spacecraft. Moreover, small organizations that wish to contribute technically are often limited by the small size of their teams and available resources, and need creative solutions for meeting mission requirements. A key need is in space-to-ground communications. Complex missions typically require large amounts of data transfer to the ground and in a timely fashion. Available options trade hardware cost, available ground stations or networks, available operating-frequency range, data-rate performance, and ease of use. A system for small spacecraft will be presented based upon Radio Frequency Integrated Circuits (RFIC) that minimizes development effort and maximizes interface control to meet typical small-spacecraft communications requirements. RFICs are low-cost components that feature pre-built radio hardware on a chip that can be expanded easily by developers with little or no radio experience. These devices are widespread in domestic applications for short-range connectivity. A preliminary design and prototype is presented that meets basic spaceflight requirements, offers data rates in the 55 to 85 kbps range, and has completed basic proof-of-concept testing. While there are higher-data-rate alternatives in existence, the solution presented here strikes a useful balance among data rate, parts cost, and ease of use for non experts, and gives the user operational control necessary to make air-to-ground communications time effective.