The viability of developing the design and manufacture of the structure of a small satellite CubeSat, at the School of Telecommunications and Aerospace Engineering of Castelldefels( EETAC), at the Polytechnical University of Catalonia (UPC), is analyzed. The design and detailed simulations of the most relevant mechanical tests have been performed by using the software SolidWorks. A honeycomb pattern monocoque structural design -called Hexagon- is proposed for a single unit CubeSat primary structure. Additionaly, Hexagon's mechanical behaviour is compared to that of the operational CubeSat structure Pumpkin. A preliminary viability study is developed, based on the results of structure simulations and theoretical studies. The resulting structure meets the corresponding CubeSat design requirements, both at the Qualification and at the Acceptance testing levels. Therefore Hexagon can be considered a viable design of a CubeSat's primary structure. After a process of research of manufacture techniques and appropriate materials, we propose to use laser sintering 3D-printing, and justify its convenience versus the use of traditional construction technologies. We suggest the material to use is a polyamide based (PA11) carbon fiber reinforced composite (PA11CF), provided by ADVANC3D Materials. We describe the construction and testing procedure and justify that the entire process can be completed by EETAC students, using equipment available to them. Finally, we propose the lines of future work to test PA11CF and, eventually, build and test the entire CubeSat structure.