Low-Earth orbit (LEO) satellite systems have been deemed a promising key enabler for current 5G and the forthcoming 6G wireless networks. Such LEO satellite constellations can provide worldwide three-dimensional coverage, high data rate, and scalability, thus enabling truly ubiquitous connectivity. On the other hand, another promising technology, reconfigurable intelligent surfaces (RISs), has emerged with favorable features, such as flexible deployment, cost & power efficiency, less transmission delay, noise-free nature, and in-band full-duplex structure. LEO satellite networks have many practical imperfections and limitations; however, exploiting RISs has been shown to be a potential solution to overcome these challenges. Particularly, RISs can enhance link quality, reduce the Doppler shift effect, and mitigate inter-/intra beam interference. In this article, we delve into exploiting RISs in LEO satellite networks. First, we present a holistic overview of LEO satellite communication and RIS technology, highlighting potential benefits and challenges. Second, we describe promising usage scenarios and applications in detail. Finally, we discuss potential future directions and challenges on RIS-empowered LEO networks, offering futuristic visions of the upcoming 6G era.

翻译：低地球轨道卫星系统已被视为当前5G及未来6G无线网络的关键使能技术。这类低轨星座能够提供全球三维覆盖、高数据速率和可扩展性，从而实现真正意义上的泛在连接。另一方面，可重构智能表面作为一种新兴技术，展现出灵活部署、成本与能效优势、低传输延迟、无噪声特性以及带内全双工结构等显著特征。尽管低轨卫星网络存在诸多实际缺陷与限制，但研究表明利用RIS可有效克服这些挑战：具体而言，RIS能够提升链路质量、降低多普勒频移效应并缓解波束内/波束间干扰。本文深入探讨了RIS在低轨卫星网络中的应用。首先，我们系统梳理了低轨卫星通信与RIS技术，重点阐释其潜在优势与挑战；其次，详细描述了前景应用场景与具体案例；最后，探讨了RIS赋能低轨网络的未来方向与挑战，为即将到来的6G时代提供前瞻性展望。