卫星已成为现代技术系统的基础性组成部分，支撑通信、导航、地球观测及科学研究等关键基础设施。随着空间探索的深入和卫星赋能服务需求的增长，对复杂、异构卫星软件的依赖持续增强。因此，系统性理解卫星软件生态愈发重要，但现有研究仍缺乏全面的经验性考察。为弥补这一空白，本文开展了首项针对开源卫星软件的特征刻画研究，对其生态系统与开发实践进行分析。我们通过三个研究问题——流行度趋势（RQ1）、软件目标（RQ2）与开发实践（RQ3）——挖掘并分析了 GitHub 上 22,286 个卫星相关项目。首先，我们刻画了项目数量与活跃开发者数量的时间演化规律，揭示其流行度持续上升的趋势；其次，通过对 646 个项目的人工审查，构建了一个涵盖概念设计、数据集、系统实现、仿真、测试及工具等六大类别的 43 项软件目标分类体系；第三，我们对含源代码的项目展开深入分析，发现该生态系统高度异构且任务高度专业化，共使用 66 种编程语言，并呈现多样化的实现策略。最后，我们总结关键发现，并为卫星开发者与研究人员提出可操作的启示。

Satellites have become fundamental components of modern technological systems, supporting critical infrastructure in communication, navigation, Earth observation, and scientific research. As space exploration advances and demand for satellite-enabled services grows, reliance on complex, heterogeneous satellite software continues to increase. A systematic understanding of the satellite software landscape is therefore increasingly important, yet existing studies still lack a comprehensive empirical examination. To address this gap, we present the first characterization study of open-source satellite software, examining its ecosystem and development practices. We mine and analyze 22,286 satellite-related GitHub projects through three research questions on popularity trends (RQ1), software goals (RQ2), and development practices (RQ3). First, we characterize the temporal evolution of projects and active developers, revealing increasing popularity. Second, through manual inspection of 646 projects, we construct a taxonomy of 43 software-goal categories spanning conceptual design, datasets, system implementation, simulation, testing, and tools. Third, we conduct an in-depth analysis of projects with source code, revealing a highly heterogeneous and task-specialized ecosystem with 66 programming languages and diverse implementation strategies. Finally, we summarize key findings and derive actionable implications for satellite developers and researchers.