Low Earth orbit (LEO) satellite mega constellations are beginning to include laser inter-satellite links (LISLs) to extend the Internet to the most remote locations on Earth. Since the process of establishing these links incurs a setup delay on the order of seconds, a static network topology is generally established well in advance, which is then used for the routing calculations. However, this involves keeping links active even when they are not being used to forward traffic, leading to poor energy efficiency. Motivated by technological advances that are gradually decreasing the LISL setup delays, we foresee scenarios where it will be possible to compute routes and establish dynamic LISLs on demand. This will require considering setup delays as penalties that will affect the end-to-end latency. In this paper, we present a nonlinear optimization model that considers these penalties in the cost function and propose three heuristic algorithms that solve the problem in a tractable way. The algorithms establish different trade-offs in terms of performance and computational complexity. We extensively analyze metrics including average latency, route change rate, outage probability, and jitter in Starlink's Phase I version 2 constellation. The results show the benefit of adaptive routing schemes according to the link setup delay. In particular, more complex schemes can decrease the average end-to-end latency in exchange for an increase in execution time. On the other hand, depending on the maximum tolerated latency, it is possible to use less computationally complex schemes which will be more scalable for the satellite mega constellations of the future.

翻译：低地球轨道（LEO）卫星巨型星座正开始引入激光星间链路（LISL），以将互联网延伸至地球上最偏远的地区。由于建立这些链路的过程会产生秒量级的建立延迟，通常需要提前建立静态网络拓扑，并以此进行路由计算。然而，这会导致即使链路未被用于转发流量时也保持激活状态，从而造成能源效率低下。受技术发展逐步降低LISL建立延迟的推动，我们预见到未来将能够按需计算路由并建立动态LISL。这需要将建立延迟视为影响端到端时延的惩罚项加以考量。本文提出了一种在成本函数中考虑此类惩罚的非线性优化模型，并提出了三种启发式算法以可行方式求解该问题。这些算法在性能与计算复杂度之间实现了不同的权衡。我们在Starlink第一阶段版本2星座中深入分析了平均时延、路由变更率、中断概率和抖动等指标。结果表明，根据链路建立延迟采用自适应路由方案具有优势。具体而言，更复杂的方案能够降低平均端到端时延，但代价是执行时间的增加。另一方面，根据最大可容忍时延的要求，可以采用计算复杂度较低的方案，这将更适应未来卫星巨型星座的可扩展性需求。