Volume 33, Issue 1

A generalized super-twisting second-order sliding mode adaptive fixed-time control law, which is used for spacecraft pose tracking in the presence of internal and external uncertainties, is proposed. Lie group SE(3) (for special Euclidean group), which is the configuration space for rigid body motion, is used for modeling the six-degrees-of-freedom dynamics of spacecraft. A fixed-time sliding mode surface is proposed and applied to design an generalized super-twisting sliding mode control law. A novel dual-layer adaption law for the controller is proposed to the ensure the gains varying rapidly with the disturbance. The adaptive second-order sliding mode controller guarantees a uniform exact convergence for the closed-loop tracking control system with less energy consumption. Numerical simulations are performed to demonstrate the excellent performances of the control law.

We present the results of numerical simulations focused on the accretion of intergalactic gas onto a gas-rich S-type disc galaxy. Our investigation explores the conditions favouring the emergence of counterrotating stellar and gaseous components within the galaxy, leading to the inflow of gas towards the central kiloparsec of the galaxy. Notably, we find that the most substantial reservoir of gas, serving as fuel for galactic nucleus activity, resides within the central region during the retrograde infall of gas at an incident angle of approximately 2 0 ° 2{0}^{^\circ } relative to the galactic plane. Departures from this angle significantly diminish the gas flow rate towards the galactic centre. Conversely, the prograde infall of intergalactic gas makes a marginal contribution to the gas content in the central region and cannot supply fuel to the active galactic nucleus. An intriguing characteristic of the observed retrograde impact is the emergence of a rotating polar ring at the galaxy’s periphery, primarily originating from intergalactic gas.

The increasing amount of massive data generated by commercial spacecraft in orbit puts forward higher and higher requirements for the stability, reliability, and computing power of computer systems for commercial aerospace data center. Data center computer systems are gradually transforming from X86 architecture and IP network model to a platform model with cloud computing and software-defined network (SDN) technology. This article proposes a new network architecture based on a unicast/multicast protocol for data interaction between the SDN and IP network. There are three main contributions of this article. The first is that the architecture proposed in this article aims to reduce end-to-end transmission latency and packet loss. The second is to improve the flexibility of system configuration and precise control when the SND controller state changes. The third is to verify the feasibility of deploying network architecture in a real data center environment.

We report the Korean records for comet C/1652 Y1, which have not been introduced in previous studies on historical comets. According to Korean historical documents, this comet, described as bai xing (white star, in literal) or ke xing (guest star, in literal), was observed with the naked eye for 22 days from December 19, 1652 to January 9, 1653. In this study, we first cross-checked the records of comet C/1652 Y1 among Korean documents and presented the translations in the Appendix for future reference. We then compared the Korean observations with the orbital path determined from calculations using the orbital elements provided by Marsden (1983. Catalog of cometary orbit. Hillside: Enslow Publishers). We also compared the illustrations depicted by Weigelius and Schiltero (1653. Commentatio astronomica de cometa novo qui sub finem anni 1652 lumine sub obscuro nobis illuxit. Jenae: Typis Georgii Sengenvvaldi) and by Hevelius (1668. Cometographia, Totam Naturam Cometarum; Exhibens. Gedani: Typis Auctoris, & Sumptibus, Simon Reiniger). We found that the Korean observations show discrepancies with the orbital path calculated by Marsden and the illustration of Weigelius and Schiltero, particularly near the end of the observation period. In conclusion, we believe that this study will contribute to improving the orbital path calculation of comet C/1652 Y1.

Polytropic equations (Lane–Emden [LE] equations) are valuable because they offer a simple explanation for a star’s interior structure, interstellar matter, molecular clouds, and even spiral arms that can be calculated and used to estimate various physical parameters. Many analytical and numerical methods are used to solve the polytropic LE equation. The series expansion method played an essential role in many areas of science and has found application in many branches of physical science. This work uses the series expansion method to examine N -dimensional polytropes ( i.e. , slab, cylinder, and sphere). To solve LE-type equations, a computational method based on accelerated series expansion (ASE) is applied. We calculate several models for the N -dimensional polytropes. The numerical results show good agreement between the ASE and numerical and analytical models of the N -dimensional polytropes.

In planetary surfaces, oblique impact events are commonplace, and their study holds significant importance for understanding planetary impact processes and aiding in the design of landers and impactors. Current research predominantly focuses on simplified models to study the force and motion under vertical impact craters in terms of scale and impact loading. For oblique impacts, investigations have primarily concentrated on the final crater shape. However, the specific influence of impact load motion on particle bed movement and the precise impact angle’s effect on the ultimate crater shape during the impact process remain unclear. In this study, we used a custom-built oblique impact experimental setup to analyze changes in the velocity field of the particle bed and the horizontal movement of the impact load. Using quasi-static region to assess ellipticity, we aimed to reveal the state of particle movement during oblique impacts and explore the impact of impact angles and energies on crater formation. The results indicate that under large impact angles, the obliquely acquired kinetic energy is minimal, leading to a predominant static point source movement of the particle bed. At higher energy levels, the impact load primarily excavates downward, resulting in the formation of circular impact craters. These findings underscore the sensitivity of particle bed motion to impact angles, making it a crucial metric for assessing the impact of oblique angles on final crater morphology.

The all-electric propulsion Geostationary Earth Orbit (GEO) satellite, characterized by its low launch cost, high precision control, and long operational lifespan, has become a focal point in aerospace research worldwide. During its orbital transfer control, this satellite continuously performs weak maneuvers across various orbits including LEO, MEO, and GEO, creating a potential “weavin” effect with other space objects, thereby dramatically increasing the risk of collisions. To effectively mitigate collision risks, this article proposes a collision warning analysis strategy based on deviation orbits. Through the categorization of warning space domain interval level, deviation orbit coverage calculation, and dynamic analysis of control parameters, a collision warning success rate of 100% is ensured. In addition, a collision avoidance algorithm based on deviation orbit control strategy is established, ensuring a 100% success rate in collision avoidance through precision calibration of electric thrust, optimization of deviation orbit control strategy, and autonomous generation of control strategy. Furthermore, a dynamic intelligent collision avoidance model based on orbit prediction error compensation is designed. By constructing an orbit prediction error analysis model, error learning model, and error compensation model, perturbation error in the orbit model are corrected, leading to an accuracy improvement of over 25% in prediction. The experimental results validate the correctness and effectiveness of the proposed methods, ensuring the safety requirements for collision warning and avoidance during the orbital transfer control process of all-electric propulsion GEO satellites.

We discovered 83 asteroids at the Baldone Astrophysical Observatory (MPC code 069) in 2017–2022. We studied one of the dynamically interesting Apollo (Near Earth object) observed at the Baldone Astronomical Observatory, namely 428694 Saule (2008 OS9) and the Centaur-type asteroid 330836 Orius (2009 HW77). We studied the evolution of the asteroid Saule’s rotation period, obliquity, and spin axis together with its non-gravitational parameter d a ∕ d t {\rm{d}}a/{\rm{d}}t connected with the Yarkovsky effect. Additionally, we studied the orbit of the Amor-type asteroid 2017 UW42, which has the significant non-gravitational parameter A 2 A2 .

Photometric study and light curve modeling for the systems V0876 Lyr, V3660 Oph, and V0988 Mon were carried out by means of their first charge-coupled device observations and the Wilson–Devinney code based on model atmospheres by Kurucz (1993. In: Milone, E. (Ed.), Light curve modeling of eclipsing binary stars. New York: Springer-Verlag. p. 93). The accepted models reveal physical parameters that show that all the primary components of the studied systems are more massive and hotter than the secondary ones. The systems V0876 Lyr and V0988 Mon were classified as over contact, with mass ratios of 0.8940 and 0.3904, respectively, while the system V366Oph was classified as detached, with a mass ratio of 0.1181. The evolutionary state of the system components was investigated, and their spectral types were adopted. Both components of the system V0876 Lyr and secondary components of the systems V3660 Oph and V0988 Mon show lower radii and luminosities than expected for Zero Age Main Sequence (ZAMS). Secondary components of the system, V3660 Oph and V0988 Mon, deviated from ZAMS and the Terminal-age Main Sequence (TAMS) with a higher radius and luminosity than expected for ZAMS and TAMS.

We study Jeans instability with generalized Maxwellian distribution. The results reveal two significant features of the modified Jeans instability. First, the Jeans wavelength of the system covers the original λ J {\lambda }_{J} when k = 1 k=1 . Second, as k k approaches 0, the modified Jeans wavelength approaches infinity. This means that the system is always gravitationally stable. Furthermore, we examine the implications of the modified Maxwellian distribution on the Friedmann equation. Our analysis suggests that the effective gravitational constant should incorporate the contribution of temperature T T in order to describe the system dynamics.

With the deployment of global navigation systems such as GPS, GLONASS, GALILEO, and BeiDou, and the construction of the global observation network, global navigation satellite system (GNSS) data have greatly expanded. Traditional relational databases and file systems can no longer efficiently store and process GNSS data. In addition, multidimensional, in-depth visual analysis methods for such data are lacking. In this paper, we provide a solution and implement a GNSS data visualization system based on MapV and cesium running on the Hadoop platform, which can effectively solve the problems of the lack of storage and computing resources for these massive multisource heterogeneous data. The proposed system provides multidimensional presentations to show how the space and ground segments of the entire system are organized by analyzing GNSS data.

To meet various requirements of the future deep space missions of China, State Key Laboratory of Astronautic Dynamics constructs a new orbit determinatin software with parallel observations process. By using 32 threads, the computational efficiency per iteration (including spacecraft’s integration) could be promoted to 10 times as that of single-threaded orbit determination. Suppose the number of observations is p p , the number of estimated parameters (including spacecraft’s state) is q q , the amount of computation of one observation is x x , the amount of computation of one Givens transformation is y y and the best number of threads is proved to be [ p ⋅ ( x + y ) / ( q ⋅ y ) ] 1 / 2 {\left[p\cdot \left(x+y)\text{/}\left(q\cdot y)]}^{1\text{/}2} for one-step threads combination. The root mean square of the postfit residuals of China’s deep space monitoring network (CDSMN) and China’s Very Long Baseline Interferometry (VLBI) network (CVN) observations in the Earth-Mars transfer phase and the Mars-orbiting phase are almost the same: about 0.3 m for Ranging, about 0.3 mm/s for Doppler, about 3 cm for VLBI delay and about 0.5 mm/s for VLBI delay rate. It is also found that all the four types of observations of CDSMN and CVN are needed in orbit determination for deep space maneuver and braking at periareion calculation. In the Mars-orbiting phase, the position accuracy after orbit determination under CDSMN-only tracking mode can reach about 1 km.

With more and more activities in cislunar space and deep space, a navigation system that can provide autonomous navigation service for cislunar or even deep space missions has become an urgent need. This article proposes a new type of navigation constellation which is placed on two kinds of special orbits, namely the dynamical substitutes around the triangular libration points and the distant retrograde orbits (DROs). Both types of orbits have the same characteristics of long-term stability under the full force model, so no orbit control is needed and it can operate autonomously without ground support. First, using inter-satellite range data, the autonomous orbit determination between navigation satellites on the dynamical substitutes and the DROs is investigated under the full force model. Then, taking a translunar orbit as an example, the constellation’s navigation performance based on inter-satellite range observation is evaluated. With range errors of 1, 10, and 100 m, respectively, the navigation capability of the constellation is successfully verified in the sense that the accuracy of the determined orbit reaches the level of the observation data. From the viewpoint of stable autonomous navigation, the current results are meaningful and deserve further consideration when deploying the navigation constellation in the Earth–Moon system.