*1.1. Replicas for Aerospace Industrial Heritage*

Heritage conservation awareness has increased and therefore, engineering graphics literature has recognized more and more research in different areas of heritage, whether industrial [8], sculptural [9], fossil [10], or architectural [11]. The term industrial heritage has been related to remains of constructions or inventions. However, in certain areas of engineering that possibility does not come to be, as it is in the aerospace sector. Therefore, space engineering projects has become critical evidence of the development of humanity, and consequently they remain part of our heritage [12]. For this reason, some researchers have demanded the need to act in the cataloguing and storage of aerospace heritage, indicating that published data are insufficient since they simply state the launch date, the name of the satellite, and the orbit [13].

Graphic representation is one of the tools that can contain and relate more information. In this sense, there are investigations focused on the use of digital representation such as the use of photogrammetry for the generation of three-dimensional modeling [14], augmented reality to visualize the industrial heritage [15], the application of BIM techniques for the representation of architectural heritage with a high level of detail [16] and the use of simplified models in educational environments to promote cultural heritage [17], including the supply of NASA stl files [18].

Photogrammetry and BIM can make a digital 3D model, the first one is faster has lower precision than the second one. Once the 3D model is created, it can be viewed digitally (augmented reality) or physically (scale model). The first has the level of detail that has been granted in digital modeling, while physical models usually entails geometric simplifications of the engineering project due to manufacturing or financial limitations. However, physical models allow a person to approach them in their real environment, so they can manipulate and understand them through the sense of touch. Meanwhile, the digital environment uses zoom or rotation tools to approach the pieces or rotate them, which can generate a distorted view of reality.

Although the 3D modeling programs have increased their use in engineering environments for the visualization and evaluation of the designed elements [19], tangible models are still indispensable because the physical interaction with the model helps to understand it, evaluate it and detect design problems [20]. The additional information incorporated in the models has been a focus of analysis in historical research [21]. In addition, it allows a more direct and personal interaction and visualization by investors, clients, designers, and other professionals who may be involved in the project.

#### *1.2. Scale Models: Architecture vs. Engineering*

The model has been a vital tool for the design of architectural projects, since it was necessary to understand and visualize large-scale buildings in different stages in order to minimize and prevent problems that might arise. The feasibility of its elaboration was based on the use of straight geometries and orthogonal angles, which can reduce three dimensions to two dimensions, and the need to simplify details in order to address reducing scale models.

However, engineering projects need to reproduce complex geometries with high detail, such as the engine of a car. For this reason, scale models in this area have normally corresponded to industrial objects, made with the same process, cost, and materials as the original one.

Likewise, scale models of small elements have traditionally been made enlarging scale (instead of full scale), which has not allowed to visualize them in the context of the project. Currently, this precision can be achieved with low cost 3D imaging, by reaching resolutions up to 20 μm in PLA (polylactic acid by fused deposition modeling) and 0.01 μm in photosensitive resin (by digital light processing—DLP). Therefore, they become a fundamental tool for the development of full scale HDMs.

In architecture and design, prototyping has been conceived as a design method to study and test how a new product is going to be used, and how it will look [19]. This concept has conceived utility in models beyond the final result, so that there are different categories for the objectives of each phase of the project design. These categories can be classified as follows [22]:


Nonetheless, technological progress has generated changes in the manufacturing process of scale models, from conventional model making to methods such as rapid prototyping. The first method involves creative approaches and is more efficient in economic terms, while the second is an automated process through a digital model of the project, and higher cost. Thus, standardization of the use of low-cost 3D printers allows complex geometries and a high level of detail to be created whether both model manufacturing methods are combined.
