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，应对环境挑战的对地观测（EO）需求急剧增长，推动其核心载体——低轨卫星数量空前激增。作为这些网络的出口节点，地面站（GS）因海量EO业务流量而面临拥塞，且其部署受制于地理、政治及预算因素。尽管星间链路（ISL）可通过将流量转发至备选地面站部分缓解拥塞，但现有基于ISL的方法难以解决因地面站分布不均引发的流量竞争，且可能因延长ISL路径引发可持续性问题。本文提出OrbitTransit——一种基于"拾取-携带-卸载"（PCO）范式的方法，利用卫星移动性实现数据\textit{投递}，并集成ISL实现流量\textit{扩散}，以缓解PCO投递固有的资源竞争。所提出的"轨道即节点"框架与避竞争投递机制联合优化混合PCO-ISL路径，在最小化能耗的同时平衡地面站业务负载。大量实验表明，与现有最优的地面站选择与路由算法相比，OrbitTransit使电池消耗降低47.16%，任务失败率下降1.09倍，并改善了地面站负载均衡。