Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： Satellite constellations are widely used for communication, navigation and Earth observation purposes. They provide good ground coverages and serve better for these needs. Of all the configurations, the Walker constellation is extensively applied in many navigation satellite systems and some low Earth orbit communication constellations, since it can be easily designed and has good coverage. Despite of these advantages, the satellites in Walker constellation generally have different ground tracks. When multiple Walker constellations are to be coordinated, in terms that the orbital planes precess synchronously with the same satellite mean motion $\Omega_1$, the semi-major axes of these Walker constellations would be significantly different even when the orbital inclinations differ by a small amount. The Space Exploration Corp (SpaceX) claimed a new constellation design in a patent for their multi-shell Starlink satellite constellation. Constellation shells with different inclinations have small altitude differences, which facilitates regulatory approval and deployment. Satellites in the same shell can also be easily designed to share the same ground track. Although they claimed these features in the patent, SpaceX shared little technical details regarding how to design these constellations. Here in this paper, we analyze the features of the Starlink constellation and try to find a practical approach to design a Starlink-like constellation, as well as how to determine the rules for inter-satellite links within the constellation.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： Tesseral perturbation is a major part in analytical orbit propagation, which involves a significant amount of calculations of inclination functions and their partial derivatives. Recursion formula is widely applied for accuracy and efficiency purposes. Based on the modified Gooding's method proposed in the literature, an optimized program is proved to reduce 24\% of calculation time for all inclination functions up to degree/order 50 ($L\le 50$). Furthermore, considering that the mean inclination varies slightly in orbit prediction for 1--3 days, the functions are expanded as Taylor series, which speeds up calculations significantly, and the time consumed during orbit prediction is reduced by 48\% while the tesseral perturbation is calculated up to degree/order 50. Moreover, with expansion of inclination functions up to the second order, the predicted ephemerides deviate slightly from those calculated using full recursion formula. For a 500\;km low Earth satellite, propagating its orbits for 3 days using modified Gooding's method and second-order Taylor expansion respectively to calculate the inclination functions within degree/order 50, the ephemeris deviation RMS (Root Mean Square) is less than 1\;mm and decreases as the altitude increases.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： The co-orbital motion occurs when a celestial body (e.g. an asteroid) shares the same semi-major axis with the perturbing object (e.g. a planet), and thus they are in a 1:1 mean motion resonance. Trojan asteroids in the tadpole orbits around planets in the Solar System are these co-orbital objects. The motion and origin of some Trojan asteroids, particularly those on high-inclination orbits, are still not fully understood. In this paper, a newly developed perturbation function expansion, which is applicable to the 1:1 resonance, is used to investigate the co-orbital motion in three-dimensional space. The position of the resonance center and the resonance width are calculated for different initial orbital elements, and the relationship between the orbital types and the initial orbital elements is analyzed. The results obtained by the analytical method are compared with and verified by the results from numerical simulations. A panorama of the co-orbital motion in the wide orbital elements space is obtained.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： The orbital eccentricity is one of the key parameters to describe the orbit of celestial bodies, which can provide important clues to reveal their dynamical evolution, and thus help to understand their formation and evolution processes along with the physical mechanisms behind them. The continuous improvement of observational technologies enables us to explore the orbit of celestial bodies beyond the Solar System, i.e., from stellar systems to planetary systems. Focusing on the orbital eccentricity of celestial bodies, this paper reviews the progress in stellar systems (including the main sequence stars, brown dwarfs, and compact stars) and planetary systems (including gas-giants, low-mass exoplanets such as ``super-Earth'' and ``sub-Neptune''), and summarizes several similarities and issues among the investigations of orbital eccentricity under different scales. Finally, based on the ongoing and future astronomical facilities and missions, we discuss the future prospect on eccentricity studies of stellar systems, extrasolar planetary systems and even extrasolar satellite systems.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： The Chinese Survey Space Telescope (CSST) is the first large space optical telescope of China. It will perform scientific observations and yield important scientific results, e.g. multi-color photometry to find and characterize exoplanets. The precision of time-domain photometry affected by various astrophysical and instrument noises is crucial for exoplanet detection and characterization. This paper constructs a time-domain model to simulate the stellar signal and various noises based on the main technical parameters of CSST published so far. The precision of photometry is analyzed by modeling the signal and noises for an example of the gazing mode in the i band. We investigate and discuss the contribution of various noises while doing aperture photometry, especially the jitter noise caused by pointing jitter and pixel response inhomogeneity. The test results also provide the recommended size of aperture photometry. Jitter noise can be suppressed by reducing jitter amplitude and uniforming pixel or by using differential photometry with reference stars. Our simulation results can be applied to the precision prediction of time-domain photometry, the refinement of CSST instrumental specifications, evaluation of exoplanet detection capabilities, and data reduction progress for CSST.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： Classical methods for initial orbit determination (IOD) include Laplace method, Gauss method and their variations. In addition to this, based on the characteristic of optical observation data nowadays, experts propose some other IOD methods, like Double-$r$ method and admissible region method. One of the ways to determinate the orbit through double-$r$ method is to guess distances of the target from the observer at two epochs---usually at the first and the last one. By doing so, we can solve the Lambert problem and use its solution as the initial guess of the orbit. Furthermore, we can improve the initial guess by iterations to reduce the root mean square (RMS) of the observations. The admissible method is based on the concept of attributable (longitude, latitude and their rates). With some conceptions, the admissible region described by the range and range rate from the observer is characterized. Using triangulation we can find the nodal point that makes the RMS minimal. In our work, we apply one intelligent optimization method---the particle swarm optimization method to the two methods, based on simulated and real data, and compare the results with that of modified Laplace method. At last, we briefly discuss the possibility of applying the double-$r$ method to the orbit link problem.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： In different orbit prediction scenarios, the dynamic models used are also different. For example, the atmospheric drag is a very important perturbation force in the prediction of space debris in low orbits, but at mid-to-high orbits, the atmospheric drag can be ignored. In order to select the most suitable dynamic models for orbit prediction in different scenarios, this article provides a large number of orbits for different accuracy requirements and different orbit types. By comparing the prediction results with different dynamic models, the optimal dynamic models for various prediction scenarios are recommended. This work can serve as references and standards for the selection of reference dynamics models for different orbital types of space debris in orbit prediction.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Over 99.9\% of the baryonic matter in the universe is plasma, hence plasma astrophysics is an important branch of modern astrophysics, which provides the sound foundation for us to understand the formation, evolution, and various eruptive phenomena in astrophysical systems. The 14 papers in this Special Issue systematically introduce the research progress in the solar and heliospheric plasmas made by the Plasma Astrophysics group in Purple Mountain Observatory, with the aim to help readers get a glimpse of the research frontiers and remaining questions.
Hits
YES
Hits
Downloads
Comment