1,720,984 research outputs found
Meta-heuristic-based design of high-order stable digital filters using pole-zero placement
No full textThis study presents a meta-heuristic optimization approach for digital IIR filter design that addresses fundamental limitations of conventional coefficient-based methods. Rather than optimizing filter coefficients directly, the proposed method identifies optimal locations of zeros, poles, and gain in the z-plane for a given frequency response. This pole-zero formulation provides an intuitive framework for managing filter characteristics, particularly stability constraints. The fitness function simultaneously optimizes magnitude and phase responses, enabling frequency response shaping for a wide range of applications. Extensive simulations across four complex design scenarios-including low-order filter, low-pass filters, curved frequency responses, and stabilized inverse systems-demonstrate the algorithm's superior performance compared to related work for high-order implementations. Results show that the proposed approach maintains strong exploration capability even in high-dimensional optimization landscapes while guaranteeing stable filter realizations. This methodology provides engineers with a flexible and reliable tool for prototyping digital filters that accommodate specific operational requirements beyond conventional filter designs.
Satellite Scanning Pattern for Optical Acquisition Considering Elliptical Shaped Field of Uncertainty
No full textThis article proposes a scan method to reduce the acquisition time of intersatellite links based on the satellite position error distribution. The errors are modeled as an anisotropic multivariate Gaussian distribution, and the field of uncertainty (FOU) is defined as the five-sigma region of this distribution. Due to the significant errors typically found in the along-track direction, the FOU often takes an elliptical shape. We propose a scanning pattern to scan the elliptical FOU efficiently. Our approach was validated through Monte-Carlo simulations and analyses using GPS data from NEXTSat-2. The results indicate that the proposed scan method is more effective than the traditional method when the FOU is more elliptical. In the case of NEXTSat-2, the efficiency of the proposed method was confirmed, with the ratio of the semiminor to the semimajor axis was less than 0.2 in 70% of cases.
Analytic pointing error evaluation on nano-satellite laser communication system
No full textThis study uses comprehensive pointing control analysis to calculate laser pointing errors for nano -satellite laser communication systems. This methodology especially enables the performance evaluation of the pointing system during the satellite pointing budget design phase. The analysis consists of a two -stage pointing approach: a body pointing stage of a satellite and a fine pointing stage within the optical payload. By simplifying each pointing stage to a single -axis model, we derive their error transfer functions, which are converted into power spectral density (PSD). The PSD of the two stages are combined using linear interpolation due to the difference in their sampling frequencies. This process yields the final laser pointing error PSD. Our method is validated against Monte -Carlo simulation results and control experiments of the fine pointing stage. The simulation and the experimental results maintained correspondence with the modeled power spectral density. These comparisons can suggest the proposed approach can predict the pointing performance of the system. Based on these results, a method to determine controller gains is introduced, aiming to minimize final pointing errors.
Multiantenna-Based Data Filling Method for Retrieving Electron Density Profiles From GNSS Radio Occultation Data
No full textRetrieval of ionospheric electron density below low Earth orbit (LEO) altitude using global navigation satellite system radio occultation (RO) sounding requires total electron content (TEC) calibration by subtracting TEC on the non-occultation side from that on the occultation side. However, this calibration is not applicable to RO missions, where the occultation antennas cannot observe non-occultation side TEC. This article proposes a methodology for retrieving ionospheric electron density through multiantenna-based data filling. The non-occultation side TEC observed by using a precise orbit determination (POD) antenna data is connected to the occultation side TEC observed by an occultation antenna, enabling the application of the calibration technique. The methodology involves modeling TEC in the remaining gap between the data from POD and occultation antennas by utilizing the Epstein function with a varying scale height. The interior-point method is used to determine the optimal parameters for the function that best fits the observations. The proposed method is validated by applying it to Korean multipurpose satellite-5 (KOMPSAT-5) data and comparing the electron densities retrieved from KOMPSAT-5 data with collocated ionosonde observations. The results demonstrate that the electron density values retrieved by the proposed algorithm are in good agreement with those obtained from ionosonde measurements.
Experimental erosion analysis and computational modeling of SiOx-coated polyimide in atomic oxygen under super-low-Earth-orbit conditions
No full textThis study investigates the erosion mechanisms and the mechanical durability of Silicon-coated Kapton HN films exposed to atomic oxygen (AO) under Super-Low-Earth-Orbit (SLEO) conditions. A ground experiment was conducted to analyze the effects of AO on silicon-coated Kapton HN films, focusing on surface erosion and chemical property changes under varying levels of AO fluence and exposure durations. The surface chemical composition and morphological changes were analyzed using X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy, Focused Ion Beam, and a UV-VIS/NIR spectrometer. The results reveal that the significant surface degradation due to AO exposure, including mass loss, chemical bond breakage, and increased roughness. Furthermore, the study identifies a three-stage erosion process in silicon-coated Kapton HN films: first, the formation of a silica layer reduced the erosion yield; second, accelerated degradation occurred after the coating is depleted; and finally, erosion stabilized as steady-state interactions between the polymer and AO are established. Based on these experimental findings, a surface erosion model was developed and employed in conjunction with the Direct Simulation Monte Carlo method. This integrated approach can predict the erosion of the AO and the durability of the SLEO satellite under various atmospheric conditions, such as the attitude of the satellite and seasonal atmospheric variations.
Fabrication of Laser-Induced Graphene (LIG) Diffractive Lenses on Flexible Coloeless Polyimide (CPI) Substrates for Aerospace Applications
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