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Lightsey,
E. Glenn
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ItemDevelopment and Testing of a 3-D-Printed Cold Gas Thruster for an Interplanetary CubeSat(Georgia Institute of Technology, 2018-03) Lightsey, E. Glenn ; Stevenson, Terry ; Sorgenfrei, MatthewThis paper describes the development and testing of a cold gas attitude control thruster produced for the BioSentinel spacecraft, a CubeSat that will operate beyond Earth orbit. The thruster will reduce the spacecraft rotational velocity after deployment, and for the remainder of the mission it will periodically unload momentum from the reaction wheels. The majority of the thruster is a single piece of 3-D-printed additive material which incorporates the propellant tanks, feed pipes, and nozzles. Combining these elements allows for more efficient use of the available volume and reduces the potential for leaks. The system uses a high-density commercial refrigerant as the propellant, due to its high volumetric impulse efficiency, as well as low toxicity and low storage pressure. Two engineering development units and one flight unit have been produced for the BioSentinel mission. The design, development, and test campaign for the thruster system is presented.
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ItemAccuracy/Computation Performance of a New Trilateration Scheme for GPS-Style Localization(Georgia Institute of Technology, 2018-03) Cheung, Kar-Ming ; Lightsey, E. Glenn ; Lee, Charles H.We recently introduced a new geometric trilateration (GT) method for GPS-style positioning. Preliminary single-point analysis using simplistic error assumptions indicates that the new scheme delivers almost indistinguishable localization accuracy as the traditional Newton-Raphson (NR) approach. Also, the same computation procedure can be used to perform high-accuracy relative positioning between a reference vehicle and an arbitrary number of target vehicles. This scheme has the potential to enable a) new mission concepts in collaborative science, b) in-situ navigation services for human Mars missions, and c) lower cost and faster acquisition of GPS signals for consumer-grade GPS products. The new GT scheme differs from the NR scheme in the following ways: 1. The new scheme is derived from Pythagoras Theorem, whereas the NR method is based on the principle of linear regression. 2. The NR method uses the absolute locations (xi, yi, zi)’s of the GPS satellites as input to each step of the localization computation. The GT method uses the Directional Cosines Ui’s from Earth’s center to the GPS satellite Si. 3. Both the NR method and the GT method iterate to converge to a localized solution. In each iteration step, multiple matrix operations are performed. The NR method constructs a different matrix in each iterative step, thus requires performing a new set of matrix operations in each step. The GT scheme uses the same matrix in each iteration, thus requiring computing the matrix operations only once for all subsequent iterations. In this paper, we perform an in-depth comparison between the GT scheme and the NR method in terms of a) GPS localization accuracy in the GPS operation environment, b) its sensitivity with respect to systematic errors and random errors, and c) computation load required to converge to a localization solution.
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ItemCupid's Arrow: A Small Satellite Concept to Measure Noble Gases in Venus' Atmosphere(Georgia Institute of Technology, 2018-03) Sotin, Christophe ; Avice, Guillaume ; Baker, John ; Freeman, Anthony ; Madzunkov, Stojan ; Stevenson, Terry ; Arora, Nitin ; Darrach, M. R. ; Lightsey, E. Glenn ; Marty, B.Getting reliable measurements of noble gases in Venus’ atmosphere with a CubeSat-derived mission concept is very challenging. But if feasible it could change how we make this fundamental geochemical measurement in planetary atmospheres and other gaseous environments (e.g., plumes emanating from icy moons or dwarf planets) across the solar system. Venus poses the most urgent and nearby target for such measurements, to fill in a key piece of the puzzle of Venus’ origin, evolution, and divergence from Earth’s geophysical history. Understanding Venus’ geophysical evolution is also key to interpreting observations of “Earth-like” exoplanets in order to assess whether they are Earth-like or Venus-like, which has obvious implications for their habitability potential. Noble gases are tracers of the evolution of planets. They trace processes such as the original supply of volatiles from the solar nebula, delivery of volatiles by asteroids and comets, escape rate of planetary atmospheres, degassing of the interior, and its timing in the planet’s history. However, a major observational missing link in our understanding of Venus’ evolution is the elementary and isotopic pattern of noble gases and stable isotopes in its atmosphere, which remain poorly known [1]. The concentrations of heavy noble gases (Kr, Xe) and their isotopes are mostly unknown, and our knowledge of light noble gases (He, Ne, Ar) is incomplete and imprecise. The Cupid’s Arrow mission concept would measure those quantities below the homopause where gas compounds are well mixed.
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ItemMicroNimbus: A CubeSat Mission for Millimeter-Wave Atmospheric Temperature Profiling(Georgia Institute of Technology, 2018-01) Himani, Tanish ; Lightsey, E. Glenn ; Frounchi, Milad ; Cressler, John D. ; Coen, Christopher ; Williams, WymanMicroNimbus is a small satellite mission being developed by the Georgia Institute of Technology and Georgia Tech Research Institute that will utilize a frequency-agile mmwave radiometer to measure and update the temperature profile of the atmosphere from a 3U CubeSat platform. The on-board radiometer instrument will provide atmospheric temperature profile data at an altitude resolution of 10 km, a geographic resolution of 0.5°, and a temperature resolution of 2K RMS. The mission strongly aligns with the goals set forth in NASA’s Science Plan and will generate data valuable to researchers in the fields of weather forecasting, LIDAR, and laser communications. MicroNimbus has passed its Preliminary Design Review (PDR) phase and is moving towards the Critical Design Review (CDR) for the mission. If successful, MicroNimbus will serve as a first step towards the creation of a constellation of satellites designed to perform near real-time temperature profiling of the atmosphere.
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ItemDesign and Operation of a Thrust Test Stand for University Small Satellite Thrusters(Georgia Institute of Technology, 2018-01) Stevenson, Terry ; Lightsey, E. GlennA small, low cost thrust test stand was developed at the Georgia Institute of Technology to support ongoing small spacecraft propulsion research. The test stand is a torsional pendulum with a low natural frequency, designed to respond to thruster pulses in the range of milliseconds to hundreds of milliseconds as if they were instantaneous impulses. The stand displacement is measured by an LVDT, and the magnitude of the oscillation resulting from the thrust is used to determine the impulse delivered. The stand is not actively damped, and is operated with less time between impulses than the oscillations take to decay. A postprocessing method was developed to separate the oscillation caused by an impulse from the previous oscillations, by fitting a damped oscillator equation before and after the impulse, and determining the instantaneous angular velocity change across the impulse. The stand was used to test a thruster developed at Georgia Tech for the NASA BioSentinel mission.
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ItemSolar Activity Investigation (SAI): A 6U CubeSat Mission Concept(Georgia Institute of Technology, 2017-12) Murphy, Neil ; Jefferies, Stuart ; Fleck, Bernhard ; Berrilli, Francesco ; Velli, Marco ; Lightsey, E. Glenn ; Gizon, Laurent ; Braun, Doug
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ItemSpacecraft Relative Navigation Using Appearance Matching and Sensor Fusion(Georgia Institute of Technology, 2017-02) McBryde, Christopher R. ; Lightsey, E. GlennIn this research, the task of object recognition and relative navigation is accomplished by fusing visible spectrum and infrared images. The appearance matching technique is briefly explained and it is shown how it can be extended to infrared images. A series of tests are performed to demonstrate the object recognition and pose estimation capabilities of the system in the visible and infrared spectra. It is also shown how the fusion of both types of images can provide greater accuracy and robustness in relative navigation than either visual or infrared images alone. Additionally, a simulation environment software tool has been developed to facilitate the creation of training images and to perform software-in-the-loop verification.
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ItemPerformance Characterization of a Cold Gas Propulsion System for a Deep Space Cubesat(Georgia Institute of Technology, 2017-02) Sorgenfrei, Matt ; Stevenson, Terry ; Lightsey, E. GlennOne challenge facing the developers of CubeSats that operate in deep space is that magnetic torque rods cannot be used for unloading the momentum stored in reaction wheels. Rather, this task is performed by a system of thrusters. While a wide variety of attitude control thrusters have been deployed on larger spacecraft, there remain very few examples of such systems being used on CubeSats. The upcoming BioSentinel mission, under development at NASA Ames Research Center, is an example of a CubeSat-class spacecraft that requires thrusters for momentum management. A new 3D-printed cold gas thruster was developed for this application. This paper will describe the test campaign that was completed for the engineering development unit (EDU), and will present a variety of preliminary results describing the performance characteristics of the thruster. The test campaign for the propulsion system EDU was carried out in partnership with members of the In-Space Propulsion Branch at Glenn Research Center in Cleveland, OH.
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ItemReference Ground Station Design for University Satellite Missions with Varying Communication Requirements(Georgia Institute of Technology, 2017-01) Choi, Thomas ; Stevenson, Terry H. ; Lightsey, E. GlennThe Georgia Institute of Technology will support five small satellite missions within a two year frame (2017 to 2019). Each satellite has different communication requirements because the mission requirements and hardware components are different for every mission. This paper discusses a common ground station architecture which will support every small satellite mission from Georgia Tech. Georgia Tech will use a network of three different ground stations, utilizing commercial off the shelf (COTS) operations software, software defined radios (SDR), and open source tracking software. This paper describes the Georgia Tech ground station and how challenges were addressed to meet the multi-mission communication requirements.
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ItemDesign and Characterization of a 3D-Printed Attitude Control Thruster for an Interplanetary 6U CubeSat(Georgia Institute of Technology, 2016-08) Stevenson, Terry ; Lightsey, E. GlennThis paper describes the design and testing of a miniature, 3D-printed cold gas attitude control thruster for the NASA Ames Research Center BioSentinel mission, an interplanetary small spacecraft that will be launched on the Em-1 flight of SLS. Earth-orbiting small satellites typically use magnetic torque rods for momentum unloading, but these cannot be employed in interplanetary space due to the lack of a strong external magnetic field. ACS thrusters can be used to unload reaction wheels or used directly for attitude control, regardless of the external environment. By 3D printing the propellant tanks, pipes, and nozzles into a single component, the complexity and cost of the thruster are reduced. The use of 3D printing also allows the thruster to better utilize its allocated volume to store more propellant. This is especially important for strictly volume-constrained spacecraft, such as CubeSats. The thruster has seven nozzles that are printed directly into the surface of the structure. The BioSentinel thruster has been tested at the Georgia Institute of Technology by the Space Systems Design Lab. The thrust of each nozzle has been measured to be approximately 50 milliNewtons, with a specific impulse of approximately 31 seconds.