Significant latency issues in global content delivery primarily arise from insufficient terrestrial network infrastructure. Deploying space-based content delivery networks within emerging mega-constellations provides an effective solution to bridging the digital divide. However, space-based caching is constrained by physical-layer dynamics, including dynamic topologies, time-varying inter-satellite link conditions, and limited onboard energy resources. Moreover, existing caching mechanisms typically lack fine-grained content categorization and comprehensive global optimization. In this paper, we proposed MegaCacheX, a cost-effective and hierarchical collaborative content distribution framework that achieves "Earth-Independence" by providing cloud services directly from space. Specifically, data centers in Sun-synchronous orbit (SSO) act as primary content sources, while caching nodes within mega-constellations and ground stations collaboratively constitute a distributed edge layer. MegaCacheX optimizes caching strategies by integrating content popularity, regional user distribution, and satellite trajectory predictions. Multi-tier caching nodes serve as service anchors, ensuring seamless content delivery with low latency. We implemented a MegaCacheX prototype on a microservices-based and containerized testbed. Evaluation results indicate that MegaCacheX reduces global content access latency by approximately 36% compared to baseline approaches, while maintaining cost efficiency.

It is critical to achieve the following objectives in partially synchronous Byzantine Fault Tolerance (BFT) protocols: (1) two-phase commit regime, (2) standard optimistic responsiveness, and (3) linear communication complexity. These three properties significantly affect the efficiency of BFT protocols. A number of attempts, such as HotStuff and Tendermint, have been made to solve this problem, but they typically manage to achieve only a subset of these properties. In this work, we propose a two-phase BFT protocol called TockCuckoo that fully achieves the aforementioned three properties. A primary challenge intwo-phaseBFT protocols is HiddenLock: when a leader lacks visibility into the latest locked block states of honest replicas, it cannot safely proceed, potentially stalling the protocol. To address this issue, we introduce the proactive voting paradigm, which explicitly distinguishes between rejection and non-receipt states. After global stable time, an honest leader can always collect sufficient votes through proactive voting, enabling quick responses. TockCuckoo operates in continuous rounds of proactive voting, ensuring responsiveness. The proactive voting process requires only linear communication overhead, which directly results in TockCuckoo achieving linear communication complexity overall. Furthermore, we introduce TockCuckoo+, an extension of TockCuckoo. By introducing a cross-pipelined design, TockCuckoo+ enables more frequent block proposals without sacrificing the key characteristics of TockCuckoo, leading to improved throughput. Our experiments in wide-area networks demonstrate that, TockCuckoo reduces commit latency by 20% to 40% compared to HotStuff across different network sizes, and TockCuckoo+ achieves a throughput increase of 1.1× to 1.5× over HotStuff.

Target tracking is a fundamental task in the domain of robotics. The effectiveness of target tracking hinges upon various factors, such as tracking distance, occlusions, collision avoidance, etc. However, few existing works can simultaneously tackle these considerations of tracking single and multiple targets in complex environments. In this study, the interaction mechanism of target tracking between the robot, the environment and the targets is analyzed, and a general measure named detectability is introduced to correlate the tracking performance for guiding robotic motion planning. Based on the detectability measure, the robotic motion planning framework based on Model Predictive Control (MPC) is proposed to achieve continuous and robust tracking of single, two and three targets in complex environments. Simulations and experiments are performed and verify the performances of our method better than the state-of-the-art methods.

Considering the limitation of off-line simulation and the high cost of many real-time simulation equipments used in aeronautical and astronautical fields, a low-cost embedded real-time simulation system has been developed for the research of satellite attitude control. By using the mature ARM/DSP chip as the processor and the embedded Linux operating system in the target machine, and the monitoring and management interface based on the graphical programming language LabVIEW in the host computer, this system has successfully addressed key technical issues of real-time simulation. It has optimized the four essential components of the satellite attitude control closed-loop system. Initial application of the system has validated its effectiveness, and therefore proved that it will be significant in the engineering applications.