 Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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- Neural Network Applied to Telescope Pointing Inaccuracy Model
Abstract: In the course of satellite observations using satellite laser ranging (SLR), a key task is pointing the telescope with high precision. Positioning the steering system’s mechanical parts with zero error is impossible. Accordingly, we must analyze and account for pointing errors by incorporating the telescope mounting errors themselves into the modeling error. Such models are far from trivial owing to the factors such as satellite azimuth, altitude, perhaps distance, or meteorological data.In this article, we explain how the data for the telescope pointing inaccuracy model (TIM) was collected and how a neural network was used to build a very precise TIM for the Golisiiv 1824 SLR station in Kyiv.We have focused our efforts on the suggested approach’s positive aspects based on our experience of using it to find practical solutions. Our practical recommendations may also be interesting for anyone working with hardware, especially in analyzing their errors. The key proof of the effectiveness of the approach is the serious increase in the number of satellites successfully tracked, especially for “blind” paths, when the satellite is not visible to the observer through the telescope guide.
PubDate: Sat, 06 Jul 2024 00:00:00 GMT
- Modeling of Resident Space Object Light Curves with Blender Software
Abstract: Modeling the behavior and shape of space objects is widely used in modern astrophysical research methods. Such studies are often used to determine the shape and modeling of physical parameters of variable stars and asteroids. Therefore, based on the database of photometric observations of resident space objects (RSO) available in the Laboratory of Space Research of Uzhhorod National University, it was decided to find a means for modeling light curves to confirm the shape of objects and determine the parameters of their rotation by analogy with objects in deep space. We attempted to use Blender software to model the RSO synthetic light curves (LCs). While Blender has been a popular open-source software among animators and visual effects artists, in recent years, it has also become a tool for researchers: for example, it is used for visualizing astrophysical datasets and generating asteroid light curves. In the process of modeling, we used all the advantages of Blender software such as Python scripting and used GPU. We made synthetic LCs for two objects – TOPEX/Poseidon and COSMOS-2502. A 3D model for Topex/Poseidon was available on the NASA website, but after research of official datasheets, we figured out that the available 3D model requires corrections in the dimensions of the RSO body and solar panel. A 3D model of COSMOS-2502 was made according to available information from the internet. A manual modeling process was performed according to well-known RSO’s self-rotation parameters. For example, we also show the results of LC modeling using the Markov chain Monte Carlo (MCMC) method. All synthetic LCs obtained in the research process are well correlated with real observed LCs.
PubDate: Sat, 06 Jul 2024 00:00:00 GMT
- Determination of the Topography-Bounded Atmospheric Gravity Correction for
the Area of Poland
Abstract: The standard recommended atmospheric gravity correction is based on the International Association of Geodesy (IAG) approach. This correction introduced into the results of gravimetric measurements reduces, in a simplified way, the influence of the actual atmospheric masses and the atmospheric masses contained inside a reference ellipsoid from the determined gravity anomalies or disturbances. Model of the actual atmosphere used in the IAG approach does not take into account topography as the lower boundary of the atmosphere, assuming that the atmosphere consists of spherical, constant density layers. In this study, we determined and analysed the components of atmospheric gravity correction for the area of Poland and its surroundings, considering topography as the lower limit of the atmosphere. In the calculations, we used algorithms typical for determining the topographic gravity reduction, assuming a model of atmospheric density based on the United States Standard Atmosphere 1976 model. The topography-bounded gravity atmospheric correction values determined were within the limits of 0.748–0.886 mGal and were different from standard, approximate atmospheric correction values in the range of 0.011 mGal for points at the sea level up to 0.105 mGal for points located at an altitude of approximately 2600 m.
PubDate: Sat, 06 Jul 2024 00:00:00 GMT
- Space Debris Capture - About New Methods of Tethered Space Net Opening by
Tubular Booms
Abstract: Nowadays, space debris is one of the main subjects of discussion regarding satellites in Earth's orbit. Right now, there are about 26,000 orbiting satellites and only few of these satellites are operational. Recently, the Polish space sector has been strongly growing and delivering instruments working in space. The first part of this paper describes the several space instruments designed in the Space Research Centre Polish Academy of Science (SRC PAS). Instruments such as SWI, RPPWI, LPPWI, Ebox or Pre-boxes have been created for a mission to Jupiter named “JUICE”. After fulfilling their scientific mission, these instruments can increase the amount of debris in space. This is one of the reasons for taking up the topic of space debris reduction and the use of technical solutions used in this mission for the proposed solution presented later.The second part of this paper describes the new methods related to space debris. The activities can be related to the space debris removal programmes. The paper describes two methods developed by Polish scientists used for removal of space debris. One of them is the new capture method and mechanism designed for it. The special mechanism is based on tubular boom application for opening the net, to capture the space debris. The main parts of the mechanism are mechanisms which have been used in the JUICE space mission. The paper describes the main idea for these new methods, and for the design part prepared the strength confirmation by structural analysis. The main function of the mechanism has been verified by simulations and tests performed in laboratories.
PubDate: Tue, 09 Apr 2024 00:00:00 GMT
- A Conceptual Open Pit Mine Architecture for the Moon Environment
Abstract: In situ resource utilization (ISRU) activities are receiving increasing attention, both from space agencies and among the international science and industrial community. Prominent examples of ongoing ISRU space programs are the NASA Artemis program and the Terrae Novae program run by the European Space Agency. In technical sciences, there are at least three groups of activities related to ISRU: prospecting bodies in the context of space missions, technological investigations related to surface infrastructure and operations, and conceptual analyses of future mining activities. The present paper belongs to the third group and brings new insights into a potential open pit mine operating on the Moon. There are several novel contributions: the definition of the objectives of the mine, based on economic indicators; a conceptual description of a pit architecture dedicated to excavating ilmenite-rich feedstock; and a qualitative and quantitative description of the chosen processes and the mine’s topology. In the paper, there are also added links to other papers connected with ISRU activities.
PubDate: Tue, 09 Apr 2024 00:00:00 GMT
- Orbit Determination of Chinese Rocket Bodies from the Picosecond Full-Rate
Laser Measurements
Abstract: In this paper, the results of the orbit determination of two Chinese rocket bodies from low earth orbit (LEO) regime based on the picosecond laser measurements provided by one laser sensor are presented. A new approach was implemented that involved using a set of single laser measurements known as full-rate measurements instead of normal points. The computation strategy was applied using three different scenarios, and several key parameters such as root mean square (RMS), RMS of position (RMSPOS), RMS of velocity (RMSVEL), and alert time were determined. The results obtained indicate that the most optimal solution is to use short orbital arcs that are 24 h long. In this case, the average RMSPOS is approximately 345–530 m, the average RMSVEL is approximately 1 m/s, and the average arc RMS is approximately 3.7–7.0 cm. The determined alert time parameter, which refers to the time during which the laser observation of a given object should be repeated, is on average approximately 19.5 h.If longer orbital arcs, such as 2 days or more, are used, RMSPOS and RMSVEL actually reach the level of single centimeters and single millimeters per second, respectively. However, the arc RMS increases significantly to at least decimeters and even above 1 m in some cases. This suggests that the long arc approach is not a favorable solution.In addition, an interesting discovery has been presented that some Chinese launchers are equipped likely with the laser retroreflectors that can easily reflect the laser beam.
PubDate: Fri, 19 Jan 2024 00:00:00 GMT
- Evaluation of Triple-Frequency GPS/Galileo/Beidou Kinematic Precise Point
Positioning Using Real-Time CNES Products for Maritime Applications
Abstract: Our research aims to evaluate the triple-frequency GPS/Galileo/BeiDou kinematic precise point positioning (PPP) accuracy for the international maritime organization (IMO) positioning accuracy and integrity requirements. The real-time Centre National d’Etudes Spatiales (CNES) satellite orbit and clock products are used to simulate real-time scenarios. GPS/Galileo/BeiDou observations are collected from a moving vessel. Both dual-frequency and triple-frequency ionosphere-free PPP models are developed. Different satellite system combinations are used, including GPS-only, GPS/Galileo, GPS/BeiDou, and GPS/Galileo/BeiDou. The GPS-only differential solution is used as a reference. It is found that both dual- and triple-frequency kinematic PPP solutions achieve the IMO accuracy requirements at 95% confidence level for ocean, coastal, port approach, port, inland waterways, and track control navigation applications, except the automatic docking application. Moreover, the PPP solutions fulfilled the IMO integrity requirements for all navigation phase applications, but the GPS and GPS/BeiDou PPP solutions did not fulfill the automatic docking integrity requirement.
PubDate: Fri, 19 Jan 2024 00:00:00 GMT
- Time Series Analysis of Landsat Images for Monitoring Flooded Areas in the
Inner Niger Delta, Mali
Abstract: This paper presents an R-based approach to mapping dynamics of the flooded areas in the Inner Niger Delta (IND), Mali, using time series analysis of Landsat 8–9 satellite images. As the largest inland wetland in West Africa, the habitats of IND offers high potential for biodiversity of the flood-dependent eco systems. IND is one of the most productive areas in West Africa. Mapping flooded areas based on satellite images enables to provide strategies for land management and rice planting and modelling vegetation types of IND. Our approach is based on using libraries of R programming language for processing six Landsat images, and each image was taken on November from 2013 to 2022. By capturing spatial and temporal structures of the satellite images on 2013, 2015, 2018, 2020, 2021 and 2022, the remote sensing data are combined to yield estimates of landscape dynamics that is temporally coherent, while helping to analyse fluctuations of spatial extent in fluvial wetlands caused by the hydrological processes of seasonal flooding. Further, by allowing packages of R to support image processing, an approach to mapping vegetation by NDVI, SAVI and EVI indices and visualising changes in distribution of different land cover classes over time is realised. In this context, processing Earth observation data by advanced scripting tools of R language provides new insights into complex interlace of climate-hydrological processes and vegetation responses. Our study contributes to the sustainable management of natural resources and improving knowledge on the functioning of IND ecosystems in Mali, West Africa.
PubDate: Fri, 19 Jan 2024 00:00:00 GMT
- Using GNSS Phase Observation Residuals and Wavelet Analysis to Detect
Earthquakes
Abstract: Global Navigation Satellite Systems (GNSSs) are one of the techniques that can be used for the deformation monitoring caused by earthquakes. GNSSs enable the monitoring of specific areas affected by earthquakes in real-time and post-processing modes. This paper provides a novel method for the short-term displacement detection based on the phase residuals of GNSS observations. The study examines a natural earthquake from October 26, 2016, in Italy with Mw 6.1. In the proposed methodology, the residuals of the GNSS phase observations are derived using Precise Point Positioning. Then, residuals are transformed to the frequency domain using a wavelet transform, and the earthquake moment is identified using the anomalies detected in the scalogram, which do not appear in stable conditions. The described methodology allows for detecting the starting and ending moments of the earthquake. The methods described detected that the moment of the earthquake is visible in the residues 8 seconds after the seismic catalog time. The conducted experiments show that the use of signal analysis tools allows it to properly detect the ground vibrations in the residuals of GNSS phase observations and thus confirms the registration of ground vibrations in satellite observation data recorded by a GNSS receiver.
PubDate: Fri, 19 Jan 2024 00:00:00 GMT
- ESMGFZ EAM Products for EOP Prediction: Toward the Quantification of Time
Variable EAM Forecast Errors
Abstract: Since more than 10 years, the Earth system modeling group at GFZ (ESMGFZ) provides effective angular momentum (EAM) functions for Earth orientation parameter assessment on a routinely daily basis. In addition to EAM of the individual Earth’s subsystems atmosphere, ocean, and hydrology, the global mass balance is calculated as barystatic sea level variation by solving explicitly the sea-level equation. ESMGFZ provides also 6-day forecasts for all of these EAM products. EAM forecasts are naturally degraded by forecast errors that typically grow with increasing forecast length, but they also show recurring patterns with occasionally higher errors at very short forecast horizons. To characterize such errors which are not randomly distributed in time, we divided the errors into a systematic and a stochastic contribution. In an earlier study, we were able to detect and remove the large systematic fraction occurring in the atmospheric angular momentum (AAM) wind term forecast errors with a cascading forward neural network model, thereby reducing the total forecast error by about 50%. In contrast, we were not able to remove the random error component assed in this study. Nevertheless, we show that machine learning methods are able to predict quasi-daily variations in time variable EAM forecasts error levels. We plan to provide these forecast error estimates along with the deterministic EAM forecast products for subsequent use in, for example, EOP Kalman filter prediction schemes.
PubDate: Fri, 19 Jan 2024 00:00:00 GMT
- Application of the Kuka Kube Test-Bed for the Hardware-in-the-Loop
Validation of the Space Manipulator Control System
Abstract: The on-ground validation of control systems designed for manipulators working in orbit is very difficult due to the necessity of simulating the microgravity environment on Earth. In this paper, we present the possibilities of utilising the KUKA KUBE test-bed with industrial robots to experimentally verify space systems using hardware-in-the-loop tests. The fixed-base KUKA industrial robot is operated in gravitational environment, while the space system model plant is solved in real time parallel to on-ground experiment. The test-bed measurements are the input of the model plant, and the output of the model is treated as an input for the industrial robot actuation. In the performed experiment, the control system based on the Dynamic Jacobian is validated. The desired point that is reached by the manipulator's end-effector is constant in the simulated environment and moving with respect to the test-bed frame. The position of the space manipulator's end-effector is calculated by evaluating dynamics of the satellite in real-time model. The results show that the control system applied to the KUKA robot works correctly. The measurements from the torque sensors mounted in KUKA robot's joints are in accordance with the simulation results. This fact enhances the possibilities of gravity compensation, thus simulating microgravity environment on the test-bed.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Sensitivity Analysis of the DEM Model Numerical Parameters on the Value of
the Angle of Repose of Lunar Regolith Analogs
Abstract: The discrete element method (DEM) is a numerical technique used in many areas of modern science to describe the behavior of bulk materials. Terramechanics of planetary soil analogs for in situ resource utilization activities is a research field where the use of DEM appears to be beneficial. Indeed, the close-to-physics modeling approach of DEM allows the researcher to gain much insight into the mechanical behavior of the regolith when it interacts with external devices in conditions that are hard to test experimentally. Nevertheless, DEM models are very difficult to calibrate due to their high complexity. In this paper, we study the influence of fundamental model parameters on specific simulation outcomes. We provide qualitative and quantitative assessments of the influence of DEM model parameters on the simulated repose angle and computational time. These results help to understand the behavior of the numerical model and are useful in the model calibration process.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Magnetic Separation of Lunar Regolith as its Beneficiation for
Construction Effort on the Moon
Abstract: A concept of magnetic separation of regolith for production of lunar aggregate is presented in the paper. Future construction effort on the Moon will require significant amounts of concrete-like composites. The authors formulate a hypothesis that magnetic separation of regolith would be a very efficient beneficiation procedure solving multiple civil engineering problems associated with properties of raw lunar soil. For the research program, 10 lunar soil simulants were used. The magnetic separation was feasible in majority of cases. Acquired lunar aggregate would be useful for both concrete-like composite production and covering the surface of a habitat. The aims of future research are pointed out in the paper.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Estimation of the Needed Regolith for Covering Lunar Habitat by Protective
Layer
Abstract: The article deals with estimation of the amount of regolith to be mined with respect to the preparation of lunar habitat. Estimation of the size of the pit is related to the overlay of regolith for habitat made of a composite concrete-like structure. The evaluation is based on the number of inhabitants, necessary floor area, and the considered structure that is made of three segments. The first segment is a linear vault with a half cylinder cross section ending with a half sphere on both sides of the vault. Elementary formulas for the computation of volume of cylinder and sphere are applied.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Application of the Obstacle Vector Field Method for Trajectory Planning of
a Planar Manipulator in Simulated Microgravity
Abstract: Capture and removal of large space debris is needed to prevent the growth of the debris population in low Earth orbit. Capture of a non-cooperative object by a manipulator mounted on a chaser satellite requires collision-free trajectory of the manipulator. The obstacle vector field (OVF) method allows to solve the trajectory planning problem in difficult scenarios. The OVF method is based on a vector field that surrounds the obstacles and generates virtual forces that drive the manipulator around the obstacles. The original formulation of the OVF method allows to obtain the desired position of the gripper, but not the desired orientation. To perform the grasping manoeuvre, the gripper has to be positioned in a specific point and aligned with the grasping interface. In this paper, we propose a modification to the OVF method that allows to obtain the desired position and orientation of the gripper. Moreover, we investigate the practical applicability of the OVF method. The OVF method is demonstrated in experiments performed on a planar air-bearing microgravity simulator. The presented results prove that the OVF method can be applied for a real system operating in simulated microgravity conditions.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Active 6 DoF Force/Torque Control Based on Dynamic Jacobian for
Free-Floating Space Manipulator
Abstract: In-orbit capture of a non-cooperative satellite will be a major challenge in the proposed servicing and active debris removal missions. The contact forces between the manipulator end-effector and the elements of the target object will occur in the grasping phase. In this paper, an active 6 Degrees of Freedom (DoF) force/torque control method for manipulator mounted on a free-floating servicing satellite is proposed. The main aim of the presented method is to balance the relation between end-effector position and force along each direction in the Cartesian space. The control law is based on the Dynamic Jacobian, which takes into account the influence of the manipulator motion on the state of the servicing satellite. The proposed approach is validated in numerical simulations with a simplified model of contact. Comparison with the classical Cartesian control shows that the active 6 DoF force/torque control method allows to obtain better positioning accuracy of the end-effector and lower control torques in manipulator joints in the presence of external forces.
PubDate: Fri, 29 Dec 2023 00:00:00 GMT
- Analysis of The Itsg-Grace Daily Models in The Determination of Polar
Motion Excitation Function
Abstract: ABSTRACTThe main aim of this study is to evaluate the usefulness of Institute of Geodesy at Graz University of Technology (ITSG) daily gravity field models in the determination of hydrological angular momentum (HAM) at nonseasonal time scales. We compared the equatorial components (χ1 and χ2) of HAM calculated with the ITSG daily gravity field models (ITSG-Gravity Recovery and Climate Experiment [ITSG-GRACE] 2016 and ITSG-GRACE 2018) with HAM and sea-level angular momentum (SLAM) from hydrological land surface discharge model (LSDM) and the hydrological signal in the polar motion excitation (known as geodetic residuals [GAO]). Data from ITSG have a daily temporal resolution and allow us to determine oscillations with higher frequencies than the more commonly used monthly data. We limited our study to the period between 2004 and 2011 because of the gaps in GRACE observations before and after this period. We evaluated HAM obtained from ITSG GRACE models in spectral and time domains and determined the amplitude spectra of the analyzed series in the spectral range from 2 to 120 days. Our analyses confirm the existence of a sub-monthly signal in the HAM series determined from ITSG daily data. We observed a similar signal in LSDM-based HAM, but with notably weaker amplitudes. We also observed common peaks around 14 days in the amplitude spectra for the GAO- and ITSG-based series, which may be related to the Earth’s tides. ITSG daily gravity field models can be useful to determine the equatorial components of HAM at nonseasonal time scales.
PubDate: Tue, 10 Oct 2023 00:00:00 GMT
- A Proposed Merging Methods of Digital Elevation Model Based on Artificial
Neural Network and Interpolation Techniques for Improved Accuracy
Abstract: ABSTRACTThe digital elevation model (DEM) is one of the most critical sources of terrain elevations, which are essential in various geoscience applications. Most of these applications need precise elevations, which are available at a high cost. Thus, sources like the Shuttle Radar Topography Mission (SRTM) DEM are frequently accessible to all users but with low accuracy. Consequently, many studies have tried to improve the accuracy of DEMs acquired from these free sources. Importantly, using the SRTM DEM is not recommended for an area that partly contains high-accuracy data. Thus, there is a need for a merging technique to produce a merged DEM of the whole area with improved accuracy. In recent years, advancements in geographic information systems (GIS) have improved data analysis by providing tools for applying merging techniques (like the minimum, maximum, last, first, mean, and blend (conventional methods)) to improve DEMs. In this article, DEM merging methods based on artificial neural network (ANN) and interpolation techniques are proposed. The methods are compared with other existing methods in commercial GIS software. The kriging, inverse distance weighted (IDW), and spline interpolation methods were considered for this investigation. The essential step for achieving the merging stage is the correction surface generation, which is used for modifying the SRTM DEM. Moreover, two cases were taken into consideration, i.e., the zeros border and the H border. The findings show that the proposed DEM merging methods (PDMMs) improved the accuracy of the SRTM DEM more than the conventional methods (CDMMs). The findings further show that the PDMMs of the H border achieved higher accuracy than the PDMMs of the zeros border, while kriging outperformed the other interpolation methods in both cases. The ANN outperformed all methods with the highest accuracy. Its improvements in the zeros and H border respectively reached 22.38% and 75.73% in elevation, 34.67% and 54.83% in the slope, and 40.28% and 52.22% in the aspect. Therefore, this approach would be cost-effective, especially in critical engineering projects.
PubDate: Tue, 10 Oct 2023 00:00:00 GMT
- Similarities and Differences in the Earth’s Water Variations Signal
Provided by Grace and AMSR-E Observations Using Maximum Covariance
Analysis at Various Land Cover Data Backgrounds
Abstract: ABSTRACTThe study presents a compatibility analysis of gravimetric observations with passive microwave observations. Monitoring the variability of soil water content is one of the essential issues in climate-related research. Total water storage changes (ΔTWS) observed by Gravity Recovery and Climate Experiment (GRACE), enables the creation of many applications in hydrological monitoring. Soil moisture (SM) is a critical variable in hydrological studies. Advanced Microwave Scanning Radiometer (AMSR-E) satellite products provided unique observations on this variable in near-daily time resolutions. The study used maximum covariance analysis (MCA) to extract principal components for ΔTWS and SM signals. The analysis was carried out for the global area, dividing the discussion into individual continents. The amplitudes of gravimetric and microwave signals were computed via the complex empirical orthogonal function (EOF) and the complex conjugate EOF* to determine the regions for detailed comparison. Similarities and differences in signal convergence results were compared with land cover data describing soil conditions, vegetation cover, urbanization status, and cultivated land. Convergence was determined using Pearson correlation coefficients and cross-correlation. In order to compare ΔTWS and SM in individual seasons, ΔTWS observations were normalized. Results show that naturally forested areas and large open spaces used for agriculture support the compatibility between GRACE and AMSRE observations and are characterized by a good Pearson correlation coefficient >0.8. Subpolar regions with permafrost present constraints for AMSR-E observations and have little convergence with GRACE observations.
PubDate: Tue, 18 Jul 2023 00:00:00 GMT
- Geodynamic Studies in the Pieniny Klippen Belt in 2004–2020
Abstract: ABSTRACTThe Pieniny Geodynamic Test Field is situated in the middle of the region between the Inner and Outer Carpathians. Geodynamic research conducted in the past in the Pieniny Klippen Belt (PKB) region were suggestive of neotectonic activity. The goal of the investigation was to determine whether the nearby structures, the Podhale Flysh (FP) and the Magura Nappe (MN), are affected by neotectonic activity in the PKB. The goal of the study was to ascertain the velocity and direction of motion of stations situated close to the Pieniny Geodynamic Test Field’s 3 main structures. Twelve GNSS stations, including 6 in the PKB, 3 in the MN, and 3 in the FP, make up the Pieniny Geodynamic Test Field. Three GNSS sites in the Tatra Mountains (TM) complete the entire geodynamic test field. The satellite observations made between 2004 and 2020 (excluding the year 2005 due to lack of observation) were investigated to identify the horizontal movements. Using the IGb14 reference system, the station’s positions and velocities were calculated. First, daily sessions were used to process the horizontal coordinates of the points for an average observation epoch in a given year. Sixteen measurement epochs were included in the long-time solution. Based on the horizontal velocity residues in the north–south and east–west directions, the station’s movement was calculated. The collected results were compared to information from the EUREF Permanent GNSS Network (EUREF) and to the findings of prior research on the tectonic activity of the PKB. The results of horizontal displacements calculated using GNSS measurements in the area of the PKB and nearby structures—the MN and the FP are presented and analyzed in this article.
PubDate: Tue, 18 Jul 2023 00:00:00 GMT
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