## 1 Introduction  
CubeSats are becoming increasingly popular in the landscape of recent space missions [1]. The main CubeSat form factors are the 1U, a cube whose side length is 10 cm [2] (app. B); the 3U, a stack of three 1 Us [2] (app. B); and the 6U, composed of two 3 Us assembled side by side [3] (app. B). A growing tendency to adopt multiple form factors, mainly 3U and 6U, can be noticed [1]. This can be due to the increasing complexity of CubeSat missions, that are mostly operated by companies and universities [1]. This recent trend to increase the spacecraft size goes against the original intentions of the CubeSat project [4], increasing the spacecraft mass and volume. This in turn may lead to higher launch costs [5] (p. 13757) and to more limited piggyback launch possibilities. The early CubeSats architecture is described by Professors [PERSON] and [PERSON] [4] (p. 7):  
\"The basic design of the satellite is comprised of a cube structure with a stack of circuit boards inside. Each face of the satellite will be covered with solar cells. The center of the satellite will have two rechargeable batteries. The batteries split the functions of the satellite into two parts. One half of the satellite contains the satellite computer, communications electronics, and attitude control system. The other half is available for a payload.\"  
This traditional architecture is still widely used today [6]. The improvement of this traditional architecture, aimed at minimizing the structural mass ratio, was recommended [7] (p. 4). Lightweight space structures have been widely researched [8] and it has been shown that the use of composite fiber-reinforced polymers (CFRPs) can reduce the 1U primary structure mass to 104.5 g [9] (p. 9). One possible approach to optimize the spacecraft volume and mass is to adopt multifunctional structures, which integrate spacecraft bus functions in the CubeSat primary or secondary structure. Multifunctional structures are already researched in automotive, aeronautical and marine applications [10; 11] at various levels of structural integration [12] (pp. 3-4). This design approach looks promising, since it has been shown that the optimization of spacecraft geometric parameters may lead to significant improvements in accomplishing the mission objectives [13]. Nevertheless, the integration of the spacecraft bus subsystems in the primary structure may represent a challenging task, due to the required miniaturization, leading to technological issues, and to the conflict between the structure and the bus subsystems requirements, for example, at the mechanical, thermal, and electromagnetic compatibility levels. The multifunctional structures design approach integrates well and further develops the ARAMIS satellite design philosophy [14]. The objective of the ARAMIS project is to design and produce a set of modular \"smart tiles\" that form the spacecraft bus. The tiles form the secondary structure of the spacecraft, i.e., the external faces of the 1U cube. They are designed to be interchangeable to reduce the design, assembly, and testing time and costs. To reduce production costs, commercial off-the-shelf (COTS) components are adopted. Within this framework, the prototype of an embedded battery tile has been designed, produced, and tested. The design of a battery tile has been chosen because batteries are an essential component of each satellite bus electrical power system (EPS). The tile design adopts composite fiber reinforced plastics (CFRP) that are lightweight and can be integrated into the design at a relatively low cost. To comply with the low cost requirement, a low degree of structural integration has been chosen [12] (pp. 3-4). Commercial lithium polymer (LiPo) batteries have been selected, rather than storing electric energy in the structure, e.g., in the CFRP components [15].