The practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols and methods. This non-standard approach requires testing and validation phases in order to optimise instrumental setups and improve data interpretation; this can occur prior to, during, or even after a mission. Flight instruments, and/or their spare models, may be evaluated using relevant terrestrial materials and/or locations. These materials are called analogues: “analogue sites” for large-scale locations, and “analogue samples” for smaller-scale materials. Depending on the scientific domain, the word “analogue” may carry different meanings but is invariably used to denote objects having compositions and/or physical properties similar to specific extraterrestrial objects. However, due to the variability in composition and properties of natural materials, there are always – inevitably – some differences between the analogue and the object(s) to which it refers. In analogue studies, it is, thus, important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone. Here, we introduce the concept of “functional analogues”. We first make an overview of the different types of analogues and sort them according to their utility. We then describe how different types of functional analogues can be used throughout the timeline of space missions, from the evaluation of different methods in the definition of a mission to understanding the results acquired by probes exploring extraterrestrial bodies. Finally, logical pathways are outlined that facilitate the selection of the best-suited functional analogue(s) according to their intended use and taking into account practical limitations.

人类和机器人行星探索固有的实际局限性要求开发特定的协议和方法。这种非标准方法需要测试和验证阶段，以优化仪器设置并改善数据解释。这可以在任务之前，期间甚至之后发生。可以使用相关的地面材料和/或位置评估飞行仪表和/或其备用模型。这些材料称为类似物：用于大型地点的“模拟地点”，用于较小规模的材料的“模拟样本”。取决于科学领域，“模拟”一词可能具有不同的含义，但总是用来表示具有类似于特定外星物体的成分和/或物理特性的物体。然而，由于天然材料的成分和特性的可变性，类似物与它所指代的对象之间总是（不可避免地）存在一些差异。因此，在类似物研究中，重要的是集中于需要模仿的特定特性，并考虑类似物特性，而不是仅考虑类似物位点或样品。在这里，我们介绍“功能类似物”的概念。我们首先概述不同类型的类似物，然后根据其用途对其进行分类。然后，我们将描述如何在整个太空任务的整个时间表中使用不同类型的功能类似物，从评估任务定义中的不同方法到了解通过探索外星体的探测器获得的结果。最后，