## 1 Introduction  
In the recent decade, the space industry has witnessed fast-paced development due to humankind's desire to explore the farthest points of space, but also to benefit as much as possible from the services that this industry can provide. This usually translates to an increase in the complexity of the instruments and payloads and, subsequently, increased power demand at the spacecraft level [1]. As the power demand increases, so does the residual heat, which will be rejected into space in order to protect the sensitive spacecraft equipment. For this, the spacecraft must use thermal control systems [2], which can be either passive or active. The former stand out for their low complexity and lack of power to operate, while the latter have the advantage of transporting higher heat quantities over longer distances [3]. In the case of modern spacecrafts, due to the increase in power generated by the satellites, which is currently as high as 20 kW [4], the most reliable solution is the use of a mechanically pumped fluid loop system (hereinafter referred to as MPFL), a type of active thermal control system that circulates a liquid with good thermal properties and transports the heat from the payloads generating it to radiators [5], which in turn reject the heat in space. The \"heart\" of the MPFL system is the pump. The pump can have multiple configurations, such as centrifugal, geared, or diaphragm pumps, each one with its advantages and disadvantages. Of these configurations, the one that stands out for spacecraft active thermal control systems is the centrifugal one. Compared to the other two, the centrifugal pump can work for long periods of time (10 to 15 years [6]--typical lifetime of a communication satellite) and it delivers a more stable flow [7]. However, according to the ESA's Technology Harmonization Dossier [8], there is a need for more and more pump development for space applications, as the ESA intends to develop and qualify a MPFL centrifugal pump for satellite active thermal control systems. Considering the above, this study addresses this subject. One of the challenges in the overall development of this equipment is the manufacturing of the pump assembly. Moreover, manufacturing of closed impellers can prove difficult in terms of meeting the required complex and precise geometries obtained by calculations for a part with such low volume and dimensions. Classical machining techniques involve a subtractive process, where material is removed from a solid block using specialized tools (mills, drills, and grinders) to achieve the desired shape. The mechanical properties are not affected by this process, and the precision can be controlled. One main disadvantage, especially for complex parts, such as the closed impeller for a centrifugal pump, is that in order to start a classic manufacturing process, a special setup is required. Depending on the impeller geometry, the part can either be made of two parts (hub and shroud), which are joined afterwards by welding, or by a single piece, in case the geometry allows it. This preparation process requires significant time and effort. The manufacturing process is divided into multiple machining steps, which generate a considerable volume of non-reusable scrap material. Due to these reasons, complex shapes are not efficient for such manufacturing processes, and for the case of the closed impeller, it is considered that obtaining the required shape by means of classical machining is sometimes impractical and/or impossible. Opposite to classical machining, additive or 3D-printing technologies represent the processes where a part is built by fusing, crosslinking, or condensing, layer-by-layer, the material [9]. For the applications in the space industry, the 3D-printing process is more suitable for a wide variety of the applications since many components are custom made.