Aerospace Science and Technology
Majid Bakhtiari; Amirhossein Panahyazdan; Siavash Sabzy
Abstract
The Earth Orientation parameters (EOPs), such as polar motion, universal time, and length of day, play a prominent role in procedures such as monitoring the Earth's rotation, weather modeling, and disaster prevention. This paper estimates the EOPs series based on a combined series approach proposed ...
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The Earth Orientation parameters (EOPs), such as polar motion, universal time, and length of day, play a prominent role in procedures such as monitoring the Earth's rotation, weather modeling, and disaster prevention. This paper estimates the EOPs series based on a combined series approach proposed by the International Earth Rotation and Reference System Observatory between 1962 and 2023, incorporating data from diverse space geodetic techniques, including DORIS, laser ranging (LLR and SLR), GNSS, and VLBI to create EOPs series. This paper proposes a hybrid deep-learning prediction model, combining a Convolutional Neural Network (CNN) and Gated Recurrent Unit (GRU) with an attention mechanism. The CNN effectively extracts and enhances features, while the GRU facilitates medium- to long-term predictions based on historical time series data. The attention mechanism prioritizes relevant data aspects, enhancing the Model's ability to discern intricate patterns, particularly for Length of Day (LOD) variations, where some covariants affect its pattern and should be considered. One of the most practical applications of these parameters is mapping the points in the terrestrial and celestial reference systems to each other. These predicted EOPs are used to create a high-accuracy coordinate transformation matrix from ECEF to ECI for applications such as high-precision navigation.
Aerospace Science and Technology
Amir reza Kosari; Ehsan Abbasali; Majid Bakhtiyari; Hamed Golpour
Abstract
The main purpose of this article is to examine the periodic coupled orbit-attitude of a satellite at restricted three body problem considering both primaries oblateness perturbations. The proposed model was based on a simplified coupled model meaning that the time evolution of the orbital state variables ...
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The main purpose of this article is to examine the periodic coupled orbit-attitude of a satellite at restricted three body problem considering both primaries oblateness perturbations. The proposed model was based on a simplified coupled model meaning that the time evolution of the orbital state variables was not a function of the attitude state variables. Since, the problem has no closed-formed solution, and the numerical methods must be used, so the problem can have different periodic or non-periodic responses to the initial conditions. The initial guess vector of the coupled model’s states was introduced to achieve the optimal initial conditions leading to the periodic responses, and then the P-CR3BP coupled orbit-attitude correction algorithm was proposed to correct this initial guess. Since, the number of periodic solutions is restricted; the suitable initial guess vector as the inputs of the coupled orbit-attitude correction algorithm increases the chances of achieving more accurate initial conditions. The initial guess of orbital states close to the initial conditions of the P-CR3BP periodic orbit, along with initial guess vector of attitude dynamics states with Poincaré mapping was suggested as the suitable initial guess vector of the coupled model.
Aerospace Science and Technology
Ehsan Abbasali; Amir reza Kosari; Majid Bakhteiari
Abstract
In this paper, the effect of perturbations of oblate primaries in the Circular Restricted Three-Body Problem is studied, and the equations of satellite orbital motion in the Circular Restricted Three-Body Problem are developed by employing Lagrangian mechanics. Since the equations have no closed-form ...
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In this paper, the effect of perturbations of oblate primaries in the Circular Restricted Three-Body Problem is studied, and the equations of satellite orbital motion in the Circular Restricted Three-Body Problem are developed by employing Lagrangian mechanics. Since the equations have no closed-form solution and numerical methods must be applied, the problem can have different periodic or quasi-periodic solutions depending on the equation's initial conditions of orbital state parameters. For this purpose, an algorithm named “orbital correction algorithm” is proposed to correct the initial conditions of orbital state parameters. The limited number of periodic orbits in the study environment indicates the algorithm’s need for suitable initial guesses as input. In the present paper, suitable initial guesses for orbital state parameters are selected from the third-order approximation of the Unperturbed Circular Restricted Three-Body Problem’s periodic solutions, increasing the chance of obtaining desired periodic solutions. The obtained perturbed and unperturbed periodic orbits are compared in order to understand the effect of perturbations. Adding the perturbations brings the study environment closer to the real environment and helps understand satellites' natural motion.