CubeSats are 10 × 10 × 10 cm small satellites, and are revolutionising access to space through their simple and low-cost design, with over 100 educational institutions and companies around the world developing their own CubeSats for educational, scientific and commercial purposes. The University of Southampton Small Satellite (UoS3) is the first ever CubeSat developed at the University of Southampton with a scientific mission to collect position and attitude data to model its orbital trajectory and validate re-entry models. The current group design project worked on finalising the design, testing each subsystem of the UoS3, integrating them into a complete system, and performing environmental tests to industry standards. Environmental testing was performed using the vacuum chamber facility at Highfield Campus, the thermal chamber and vibration shaker table facilities at the National Oceanographic Centre (NOC), and the thermal vacuum chamber at TS-Space Systems in Marlow. The UoS3 is participating in the European Space Agency (ESA) 2017 Fly Your Satellite! (FYS) programme to be considered for a launch opportunity, competing with other European and Canadian universities. The team was invited to and has since presented at the FYS Selection Workshop in the ESA European Space Research and Technology Centre (ESTEC), Netherlands.