1,720,958 research outputs found
Design, Development and Testing of an Attitude Determination Experiment for the European Student Earth Orbiter
No full textThe European Student Earth Orbiter (ESEO) is the main educational project of the European Space Agency that allows students to design, develop and test scientific payloads. The contribution to be made by the TU Delft is a software-based Attitude Determination Experiment (ADE) that contains four different algorithms for attitude estimation that are to be tested in-situ for comparative analysis through the telemetry sent down by the satellite. The four algorithms are the Optimal REQUEST, the Additive Quaternion Kalman Filter, the Pseudolinear Quaternion Kalman Filter and the Multiplicative Extended Kalman Filter. The Additive Quaternion Kalman Filter has been further adjusted with the incorporation of the Maximum Information Rate Filter, which reduces the measurement matrix into six candidates and selects the one corresponding to the highest information rate for use in the algorithm. Though this filter has the benefit of using reduced matrices, computational efficiency is only really increased if the selection process is as computationally lean as possible as well. Therefore, an analysis was performed of the selection pattern of the Maximum Information Rate filter. This analysis shows that a clear pattern exists for the Earth sensor (based solely on the hemisphere), a more complicated pattern is visible for the Sun sensor, while the magnetometer has no useful pattern to speak of. The ADE has been programmed in the C-language and adjusted for the RTEMS real-time operating system. All operations to be performed by the payload have been verified to operate within the assigned budgets and limitations of the hardware on board the satellite. The payload is capable of running the four algorithms within 100 milliseconds while retaining a code size 24 kB, which is lower than the 35 kB budget and a memory size of 8.8 kB, which is lower than the 10 kB budget. All algorithms have undergone extensive Monte-Carlo simulations to test for stability and sensitivity to the involved parameters. All algorithms manage to retain a steady-state angular estimation error lower than 0.5 degrees under conditions varying by about 30% from the expected parameters. At the time of writing, the ADE has passed the Critical Design Review and is ready to be integrated onto the ESEO satellite.Space EngineeringEarth Observation and Space SystemsAerospace Engineerin
Photovoltaic Concentrator Cells: Electro-Thermal Modelling And Experimental Analysis
No full textAn interesting concept related to photovoltaic energy is Concentrated Photovoltaics (CPV), in which sunlight is focussed on a PV cell through lenses and mirrors, thereby increasing the incident irradiance on the PV cell. Solar concentration is proven to not only increase the output power of PV cells, but also to increase the electrical efficiency of PV cells. This concept is expected to further push PV energy to the scale of MW power plants for large-scale energy production, and increase the power density of standalone PV modules on Earth and in space. Increasing the irradiation on a PV cell inevitably also increases the temperature of the PV cell due to thermal losses. Cell temperature has a negative effect on the output power and electrical efficiency of a PV cell, and given a high enough concentration ratio, may cause the PV cell to lose electrical efficiency and ultimately break down. Adequate cooling is therefore required for CPV systems to keep the PV cell in its optimal operating temperature range. For this purpose a model is proposed that simulates the output characteristics under influence of solar concentration and temperature variations, most notably the output power and electrical efficiency of a PV cell. The electro-thermal model is fundamentally based on the detailed balance model, which dictates that the absorbed and emitted photon flux must be equal in equilibrium conditions. From detailed balance, the absorption, recombination and photo-generation processes in a PV cell are determined, from which the Shockley-Queisser limit is deduced. This fundamental model is extended to the single-diode model, which serves as the ultimate baseline of PV simulation, taking into account cell temperature, concentration ratio and other internal PV cell factors. Sensitivity analyses on the single-diode model show that solar concentration indeed increases the output power and electrical efficiency. Taking into account solar concentration and temperature effects however, shows that the electrical efficiency drops by 4% points at a concentration ratio of 20, thereby confirming that without cooling, increasing the solar concentration on a PV cell will yield lower electrical efficiencies due to thermal effects. Laboratory experiments are conducted on an Emcore 3J gallium-arsenide PV cell (DUT) to verify the electro-thermal model. Baseline tests are conducted using a calibrated light source, and secondary tests involving a secondary light source are performed at controlled ambient and elevated temperatures. These results show that the model has a fit of 98.9% with respect to the verified specifications of the DUT PV cell at an ambient temperature of 25 ◦C. At an elevated cell temperature of 60 ◦C, discrepancies exist between the simulated single-diode model and test results. A new in-plane heat conduction concept developed by Airbus NL called Hiper is added to the test set-up to assess its suitability in conjunction with a heat radiator for PV cells. Hiper is a novel thin-film material particularly suited to spread heat effectively over a surface, from which it can be dissipated using a radiating material. Experimental results show that heat is spread slightly more effectively with Hiper, than in the same test set-up without Hiper, highlighting its heat spreading capabilities.Aerospace EngineeringSpace EngineeringSpace Systems Egineerin
System design and orbit analysis for SpooQySat-1.
No full textThe Center for Quantum Technologies (CQT), which belongs to the National University of Singapore (NUS) is developing a nanosatellite to host their miniaturized Quantum Key Distribution (QKD) payload called SPEQS. QKD makes it possible to generate encryption keys through the use of strongly correlated photons. This would allow two parties to securely communicate with each other without any possibility of their conversation being hacked. CQT has already demonstrated a QKD free space-link in 2005. The main challenge now lies within the creation of a global QKD network. One possible way to do this is through the use of nanosatellites. As CQT has no experience in designing nanosatellites, a first step towards this goal is to design a satellite which allows the team to test a version of their payload. The main purpose of the thesis work is to present a reliable design for CQT’s first nanosatellite, SpooQySat-1, through the implementation of a systems engineering approach. The requirements as first defined by CQT are revised and redefined through the use of a requirements discovery tree. After the requirements list was complete, an orbit analysis has been carried out to ensure the best suitable orbit was selected for the mission. This, together with the requirements, served as input for the design analysis. A concept of operations has been generated, leading to a realistic power budget that has been compared to the estimated incoming power for various cases. A communication analysis has been carried out taking into account the noisy environment of Singapore. COTS component selection has been carried out for all subsystems. To ensure maximum reliability, a risk analysis has been implemented. Data regarding CubeSat failures has been gathered to inform the risk analysis. The outcome of the risk analysis was a mitigation strategy that allowed a new design iteration to ensure maximum reliability.Space System EngineeringAerospace Engineerin
Broadband Liquid Dampers to Stabilize Flexible Spacecraft Structures
No full textMass-spring and liquid dampers enable structural vibration control to attenuate single, coupled lateral and torsional vibrations in diverse structures. Out of these, the passively tuned liquid damper (TLD) class is wanted due to its broad applicability, extreme reliability, robustness, long life time and ease of manufacturability. In this PhD thesis, the theory, design, verification and validation of multi-mode TLDs in terrestrial and mainly spacecraft (S/C) applications have been studied. The most challenging TLD design of the type “tube-with-endpots” was the Chinese meteorological FY-2 S/C nutation damper in the 90s. The extreme performance requirements like the 0.5” residual nutation damping angle implied an extended test program which led to refined insights in the recursive calibration method and limiting damping performance. The test analysis results and the involvement in the in-orbit analysis of the Ulysses S/C nutation anomaly in the same period, led the author to the idea of a multi-mode TLD system. The concept was proposed and successfully applied in the Cluster S/C for the effective damping of both nutation and coupled wire boom (antenna) oscillation modes. To come that far, the essentials of spacecraft dynamics and its control required an extension of the liquid flow models and an appropriate TLD design methodology to include multi-mode excitations. The TLD key performance parameters are the dissipation rate, residual damping angle and the resonance frequency which is directly related to the effective damping length. This parameter used to be obtained by an educated guess on basis of test heritage. The existing practical design rules, however, were overruled by new insights which are based on the latest scientific results from fluid mechanics. This knowledge and the extensive analysis of all available TLD damping performance tests resulted in a new refined methodology to estimate the effective damping length properly. The eventual value, however, must still be determined via recursive calibration cycles but better initial estimates reduce the required test times significantly. The residual damping angle is limited by the TLD endpot behavior which is determined by the physics of the liquid meniscus interaction with the endpot wall. Though the TLD design is characterized by a very low residual angle with almost zero dead-band, the very limit is not clear. This issue was investigated using multiple models and experiments whilst the state-of-the-art in the scientific literature from nano-tribology and wetting transitions on biomimetic surfaces was explored. Test refinements are proposed to decrease damping fluctuations and extend the low angular test range. Although, the limiting angle is not known, there is strong evidence that the limits can be extended beyond the 0.1” flight value. The early design phase of the broadband Cluster TLDs in 1991 and the TLD developments up to 2012 were studied. Moreover, the spin-stabilized magneto-spherical S/C Bepi-Colombo, Cluster, RBSP, DICE, Themis and FAST are compared which confirm the applicability of the multi-mode TLD concept. The study of the generic theory of wire boom oscillations, gyroscopically coupled to the S/C hub spin and nutation modes, resulted in a new harmonized parameterization and derived equations. The Cluster TLD system with in addition the internal wire boom damping enable the boom deflection limit and its damping time constant to be design parameters. On basis of this knowledge, a recursive bottom-up TLD design methodology was developed. The stability study including the wire boom composition made clear where the limit of multi-mode modeling is reached and breadboard experiments and practical engineering trade-offs are required. The optimal wire boom deployment strategy using the multi-mode damping principle was analyzed. At small angular deflections, however, material artifacts and anelastic flexure dominate and only dedicated engineering tests can clarify these issues. The current status of the TLD design was investigated by comparing the RBSP S/C [2012] ring TLD and the Cluster S/C [2000] endpot TLD designs. The combination of the Cluster TLD bottom-up design methodology with the 9 degrees of freedom RBSP top-down model completed the model base for the design of multi-mode TLDs in flexible S/C. The RBSP TLD suffers with considerable angular off-sets and inrush time constants which are not accounted for in the RBSP model. The Cluster TLD design, however, lacks these artifacts. RBSP S/C flight validation data, however, are not yet available. The nutation related Cluster flight data validate the TLD model predictions firmly within the requirements. This renders an indirect but incomplete prove of the effectiveness of the TLD system design. It is hard, however, to trace and validate the designed multi-mode performance itself. It is, therefore, of great scientific value to obtain Attitude Determination and Control System flight data. A successful TLD development requires risk mitigation as an essential part of systems engineering (SE). An inventory of boundary conditions was made thinking ahead for production and project cost escalations. In the high-tech industry, however, there is little focus on a scientifically based bottom-up SE approach though such effort does pay off. It was one of the quests of this thesis to prove the added value of such an investment. As a result, the developed methodologies do contribute to a profound SE approach in the development of multi-mode TLDs. The space qualified broadband TLD design with endpots is an excellent choice for use in future spin-stabilized S/C with wire boom configurations. The results of the PhD thesis enable the extreme refinement of the given damper concept. Market research and the allocation of dedicated solutions are a way towards valorization. Terrestrial spin-offs in the engineering fields of refined (ultra) centrifuges, pulsating industrial piping systems, windmills, earthquake control of building structures, shipbuilding and bridge stabilization offer the best valorization opportunities in short terms.Earth Observation and Space SystemsAerospace Engineerin
Heliodromus: Renewable energy from space
No full textClimate change and the related running out of fossil fuel reserves drive the development of renewable energy sources. To contribute to a solution of these problems, we present the results of a BSc student design synthesis exercise project on Space Based Solar Power (SBSP). A SBSP system generates power in space using solar cells concentrator systems and wireless power transmittance to Earth. Main advantages compared to terrestrial solar conversion systems are a higher surface power density and continuous power supply. The project includes an analysis of the current and future electricity market, its technical performance, the conceptual design of a SBSP system, the economical aspects and sustainability. The SBPS top level requirements are an operational lifetime greater than 10 years, an end of life effective power output on Earth exceeding 1 GW, a launch before 2025 and being cost-competitive with terrestrial energy sources. Besides these top level requirements, numerous derived requirements are established on sustainability, safety and (subsystem) design. The SBPS concept, termed Heliodromus, resulted from a broad study starting with three existing concepts. A systems engineering tradeoff resulted in a new constellation concept: Ten satellites orbiting in Low-Earth Orbit and two satellites orbiting in geostationary Earth orbit each having five mirrors. The performance of Heliodromus was evaluated by the following criterea: overall efficiency, technical readiness levels, energy payback time and total cost. The major losses occur during the initial energy conversion, with only 15% efficiency, by the photovoltaic thin films. Heliodromus is 5 to 10 times more expensive compared to existing Earth based solar farms, both photovoltaic and solar dynamic. The energy payback time is 6 years compared to 3 years for terrestrial solutions. The worst case estimate of Heliodromus' efficiency is 2% which is not sufficient to compete with Earth-based solar systems. However, due to the ongoing rapid developments, an overall efficiency of 10% efficiency is credible in the present decade. The (worst case) electricity cost is 1 per kWh for a (2010) terrestrial power plant. The cost of Heliodromus is around $98 billion and at this stage it is not price-competitive with fossil or Earth-based renewable energy sources. The required assembly in orbit was never done on the scale required for Heliodromus, therefore it opens totally new fields of research and development. The total efficiency was defined worst case but the improvement of electronic components efficiency will continue. Therefore a factor 5 improvement in the near future is probable, getting Heliodromus closer to becoming market viable.Space EngineeringAerospace Engineerin
Advanced Nano Telescope: A cornerstone solution in Earth Observation
No full textRecent developments in satellite industry gaining strong attention are so called nanosatellites. These small satellites, with sizes of about a milk carton, are easy to build and much more adordable, promising great advantages for future space missions. Up until today no reliable mid-resolution Earth observation instrument has been build that can be operated on such a small, low cost satellite. In light of these events this years Design Synthesis Exercise group 9 developed such a camera system which is called the Advanced Nano Telescope (ANT) providing a novel instrument that can be carried as payload by nanosatellites. The novelty lies in the applied principles of miniaturization and intelligent distribution in order to compete with a single large scale instrument. The strength of the instrument developed lies in the fact that it can take images with 7.5 meter resolution, requiring a volume of only 10 x 10 x 15 cm at an estimated cost about EUR 100,000. The small dimensions allow it to ft into half a standard 3 unit CubeSat such as the Delfi-n3Xt. The resolution is achieved by limiting the system to sense a narrow band around a single color, making use of a well designed combination of lenses and mirrors folding the light path enabling a long focal length. The thermo-mechanical design is designed such that the instrument functions in the hostile space environment from altitudes of 540 to 1440 km altitude. ANT has a smart modular structure that allows a mission designer to simply purchase the instrument and plug it into a satellite. Since all required electronic components are already present in the instrument the host satellite only needs to provide power and pointing capability to be able to achieve a fully functional system. One ANT by itself can take mid-resolution mono-chromatic images, but its real value will show when it is launched in a constellation, something which the low cost per unit allows. Multiple constellations of ANT's can outperform single satellites systems with similar ground resolutions in terms of development time, construction costs, operating costs and revisit time, enabling color composite imagery and promising improved availability at a lower price per image. Furthermore dedicated relay satellites can be added to achieve higher data rates. Overall catastrophic failures are eliminated as multiple satellites performing independent tasks are present offering redundancy and the possibility of replacement. The conclusion is that the system developed holds a promising future with a wide range of possible applications. The instrument itself is striking due to its apparently simple but intelligent and robust design enabling Earth observation without the need of expensive large scale satellites. For future work it is recommended to further develop the concept in order to prototype and test the actual performance of the ANT instrument.Bachelor Aerospace EngineeringSpace EngineeringAerospace Engineerin
Thermo-Optical System Design of the Delft Deployable Space Telescope Baffle
No full textFurther development of the Delft Deployable Space Telescope (DST) was needed to solve for defocus due to thermal expansion. This thesis focuses on implementation of stray light design methodology on the deployable baffle to provide a more stable temperature environment. This methodology utilises various baffle shapes and the arrangement of vanes to absorb or reflect incoming light to the desired location. The effect on the thermal and stray light performance is analysed, to gather insight to form several baffle concepts. These are put in a trade-off with thermal and stray light performance in mind. The result is a deployable baffle using four vanes which increases the compliance to the defocus requirement by 28% for the visible light version of the DST. The baffle for the thermal infrared DST is a cylindrical baffle with one vane with a 100% compliance to the defocus requirement. The thesis provides the design of the baffle which reduces the defocus and reduces stray light.Delft Deployable Space TelescopeAerospace Engineerin
Design of the Secondary Mirror Support Structure for the Deployable Space Telescope
No full textThe thesis discusses the design of the secondary mirror support structure for the deployable space telescope. In the thesis the entire support system is considered, including system layout and mirror interface. A selection of hinge concepts were identified and final concepts were selected in trade-offs. The mid hinge was selected to be an integral slotted hinge, while the top and root hinges were selected to be CORE hinges. The concepts for the root and top hinges were worked out in detail to a point that the hinges can be produced and tested. Thermal and launch loads were considered during the detailed design of these hinges. Furthermore, it was investigated what the effect of adding ribbons to the structure was on the response of the system to harmonic disturbances. The results of this thesis can be used to produce a breadboard for testing the secondary mirror support structure, and as a baseline for further design work on the secondary mirror support structure.Deployable Space TelescopeAerospace Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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