Low-Earth Orbit (LEO) satellites are increasingly proposed for communication and in-orbit computing, achieving low-latency global services. However, their sustainability remains largely unexamined. This paper investigates the carbon footprint of computing in space, focusing on lifecycle emissions from launch over orbital operation to re-entry. We present ESpaS, a lightweight tool for estimating carbon intensities across CPU usage, memory, and networking in orbital vs. terrestrial settings. Three worked examples compare (i) launch technologies (state-of-the-art rocket vs. potential next generation), (ii) operational emissions of data center workloads in orbit and on the ground and, (iii) in-orbit aggregation with raw data transmission. Results show that, even under optimistic assumptions, in-orbit systems incur significantly higher carbon costs - primarily due to embodied emissions from launch and re-entry. Our findings advocate for carbon-aware design principles and regulatory oversight in developing sustainable digital infrastructure in orbit.

翻译：低地球轨道（LEO）卫星越来越多地被提议用于通信和轨道计算，以实现低延迟的全球服务。然而，其可持续性在很大程度上仍未得到审视。本文研究了太空计算的碳足迹，重点关注从发射、轨道运行到再入的整个生命周期的排放。我们提出了ESpaS，这是一个轻量级工具，用于估算轨道与地面环境中CPU使用、内存和网络活动的碳强度。通过三个实例分析，我们比较了：（i）发射技术（最先进的火箭与潜在的下一代技术），（ii）轨道与地面数据中心工作负载的运行排放，以及（iii）轨道数据聚合与原始数据传输。结果表明，即使在乐观假设下，轨道系统的碳成本也显著更高——这主要源于发射和再入过程所蕴含的排放。我们的研究主张，在开发可持续的轨道数字基础设施时，应采用碳感知设计原则并加强监管。