The emerging demand for Earth observation (EO) to address environmental challenges has driven unprecedented growth in its primary carrier, Low Earth Orbit satellites, in recent years. Ground stations (GSs), the egress points of these networks, are congested due to the massive volume of EO traffic, and their deployment is constrained by geographic, political, and budgetary factors. Although inter-satellite links (ISLs) can partially relieve this congestion by forwarding traffic to alternative GSs, existing ISL-based approaches can hardly address traffic contention caused by biased GS distribution and may also raise sustainability concerns due to prolonged ISL paths. In this paper, we propose OrbitTransit, a pickup-carry-offload (PCO) approach that leverages satellite mobility for data \textit{delivery} and integrates ISLs for traffic \textit{diffusion} to alleviate the resource contention inherent in PCO delivery. The proposed orbit-as-node framework and contention-avoidant delivery jointly determine the optimal hybrid PCO-ISL path, minimizing energy consumption and balancing GS traffic. Extensive experiments show that OrbitTransit reduces battery consumption by $47.16\%$, decreases task failures by $1.09\times$, and improves GS load balancing compared with state-of-the-art GS selection and routing algorithms.

翻译：近年来，为应对环境挑战而对地观测（EO）的需求日益增长，推动了其主要载体——低地球轨道卫星的指数级发展。地面站（GS）作为这些网络的出口节点，因海量EO流量而面临拥堵，其部署还受地理、政治和预算因素制约。尽管星间链路（ISL）可通过将流量转发至替代地面站部分缓解拥堵，但现有基于ISL的方法难以解决因地面站分布不均衡引发的流量竞争，且长距离ISL路径可能引发可持续性问题。本文提出OrbitTransit——一种“取-载-卸”（PCO）方案，利用卫星移动性实现数据*传输*，并融合ISL实现流量*扩散*，以缓解PCO传输固有的资源竞争。所提出的“轨道即节点”框架与竞争规避传输策略协同确定最优混合PCO-ISL路径，在最小化能耗的同时平衡地面站流量。大量实验表明，与现有最优地面站选择及路由算法相比，OrbitTransit可将电池消耗降低47.16%，任务失败率减少1.09倍，并显著提升地面站负载均衡性能。