The rapid deployment of Low Earth Orbit (LEO) satellites, driven by technological advancements and cost reductions, has led to the emergence of mega-constellations for satellite-based Internet services. Among them, the networking problem has become a significant area of research. Specifically, breaking away from the traditional Grid-Mesh + topology schemes has been a focal point. Although some related studies have been conducted, there are still three major challenges in optimizing the topology of laser inter-satellite links: the lack of theoretical derivation for satellite visibility, the need for comprehensive modeling goals, and the absence of network simulation verification. To address these challenges, we introduce the theory of visibility analysis of laser terminals in real scenarios and propose a theoretical model of topologically feasible solutions for integer linear programming. Furthermore, a mathematical model is developed that considers time delay, hop count, and link load as optimization objectives. The Many-objective Non-Grid-Mesh Topology Optimization (M-NGTO) algorithm, based on Non-dominated Sorting Genetic Algorithm III (NSGA-III), is then designed to effectively optimize the topology. The optimized Non-Grid-Mesh topology is validated through packet-level simulations on the Hypatia platform. Additionally, consistency analysis is performed to establish agreement between theory and simulation results. The results of simulations conducted on two megaLEO satellite Internet constellations, GW and Starlink, demonstrate that the performance of the Non-Grid-Mesh topology in the above three optimization objectives is approximately 39.11% better than the average of the Grid-Mesh + topology, confirming the effectiveness of the M-NGTO algorithm. The findings have significant implications for enhancing the communication performance and load balancing of satellite Internet systems.

Given the crucial role of the earth observation satellites in numerous key applications, using Low Earth Orbit (LEO) satellite internet as intermediaries via Laser Inter-Satellite Links (LISLs) has emerged as a promising solution to help transmit substantial amounts of observation data to ground stations. For Very Low Earth Orbit (VLEO) observation satellites, optimizing the cross-layer topology between themselves and LEO communication satellites has become paramount. To mitigate existing centralized algorithms’ reliance on global data transfer requirement information, a Novel Distributed Interactive Mechanism (NDIM) for cross-layer LISL establishment is proposed. Here, the VLEO observation satellite decides its own access strategy based on local network information gleaned from three information exchanges with the LEO communication satellite. Within this mechanism, the cross-layer link optimization is performed via the formulation of a multi-objective topology optimization model, which considers the transmission requirements of observation satellites, load balancing amongst the communication satellite layer, and the transmission delay of emergency tasks. Based on this framework, we propose a Distributed Multi-objective cross-layer Topology Optimization (DMTO) algorithm. Our algorithm is novel in considering the remaining load of the intermediary communication satellites, and it allows observation satellites to decide on access plans on demand, given incoming data. Additionally, we used real data from Typhoon LEKIMA to establish a multi-task scenario and conducted packet-level simulations based on the Starlink and Dove constellations. The results indicate that, compared to the existing baseline, the DMTO algorithm increased the observation data throughput by 1.37% (326.95 GB) and reduced the average transmission delay of emergency task data by 4.20% (20.5 seconds).

With the rapid development of large-scale Low Earth Orbit (LEO) satellite internet, Very Low Earth Orbit (VLEO) Earth observation constellations are increasingly using Inter-Satellite Links (LISLs) for cross-layer access to Internet satellites. It is an effective means to enhance data return throughput. When both observation and communication satellite constellations use lasers for networking, cross-layer access between the VLEO and LEO satellite networks requires reallocating lasers. This reallocation disrupts the original topology and impacts network performance. To maximize the collaborative operational efficiency of the double-layer network, we fundamentally analyze the relationship between topology links, throughput, and delay using graph and queuing theory. Innovatively, we discover the superiority of two axioms in addressing the cross-layer topology optimization problem, including the “Minimum Hop Count” and “Minimum Overlap Path”. Based on these axioms, a many-objective cross-layer topology optimization model is established that considers the hop count and the average link utilization frequency of both VLEO and LEO satellite networks. To reduce the reliance on centralized algorithms on global transmission demand, a Local Distributed Interaction Mechanism (LDIM) is proposed for cross-layer LISL establishment. An onboard Novel Distributed Many-Objective Topology Optimization (NDMTO) algorithm is also introduced for VLEO satellites to manage access strategies. Finally, we use real data from Typhoon LEKIMA to create a multi-task scenario and conduct packet-level simulations based on the Starlink and Dove constellations. The results indicate that, compared to existing benchmarks, the NDMTO algorithm improves data throughput by 26.73% and reduces the average transmission delay of emergency task data by 20.7%.

The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations. This operational mode relies heavily on the support of ground stations. To enhance the high-precision autonomous timing capability of next-generation navigation satellites, it is necessary to autonomously generate a comprehensive space-based time scale on orbit and make long-term, high-precision predictions for the clock error of this time scale. In order to solve these two problems, this paper proposed a two-level satellite timing system, and used multiple time-keeping node satellites to generate a more stable space-based time scale. Then this paper used the sparse sampling Long Short-Term Memory (LSTM) algorithm to improve the accuracy of clock error long-term prediction on space-based time scale. After simulation, at sampling times of 300 s, 8.64 × 10⁴ s, and 1 × 10⁶ s, the frequency stabilities of the spaceborne timescale reach 1.35 × 10^–15, 3.37 × 10^–16, and 2.81 × 10^–16, respectively. When applying the improved clock error prediction algorithm, the ten-day prediction error is 3.16 × 10^–10 s. Compared with those of the continuous sampling LSTM, Kalman filter, polynomial and quadratic polynomial models, the corresponding prediction accuracies are 1.72, 1.56, 1.83 and 1.36 times greater, respectively.

The application of the new type Atomic Frequency Standard (AFS) and the onboard clock ensemble technology is the evolution trend to realize the high precision and stability space-based time reference establishment and maintenance for next-generation Global Navigation Satellite System (GNSS). The architecture upgrade with ensemble clock group management mode provides the on-orbit continuous direct measurement and autonomous fault detection and recovery of the AFS group. This research proposes a framework of the GNSS robust heterogeneous ensemble clock system which includes the two-stage Kalman filter logic structure. For the application scenario of single satellite resilient Ensemble Time Scale (ETS) generation, a resilient Kalman Plus Weights (KPW) time-scale algorithm considering dynamic weight factors is designed, and its robustness against clock outages and anomalies is analyzed when using multiple heterogeneous AFS configuration presets. Then an intuitive and practical strategy of control parameter determination is introduced to support the Linear Quadratic Gaussian (LQG) control model to generate appropriate control inputs for optimal frequency steering. The simulation results show that the spaceborne composite clock signal combines the advantages of short and long-term frequency stability, and improves the overall stability performance compared with a single AFS. The long-term stability of the designed primary timekeeping satellite node can reach 4.68E-16/1day and 5.71E-16/1day respectively when adopting two heterogeneous AFS configurations. The research results are expected to be applied to the next-generation GNSS spaceborne time-frequency system development, and improve the operational robustness and autonomous timekeeping capacity of the ensemble clock group.