In 2007, the Government of Costa Rica announced to the world its ambitious goal of turning into the first carbon neutral country by 2021. Following the announcement, governmental institutions, universities, NGOs and private companies have worked arduously on the creation of different initiatives to reach that goal. One innovative project is Irazú, consisting of the design, construction, launch, and operation of the first Central American satellite. The project is not just intended to enable a baseline for training scientists, engineers, and managers in the necessary skills to execute an end-to-end space project. It also aims to demonstrate a CubeSat Store & Forward (CS&F) System that enables transmission of biomass and carbon dioxide fixation data from a remote fast growth tree plantation in the lowlands of Costa Rica to a research facility for its post-processing and analysis. The Irazú project is led jointly by the Central American Association for Aeronautics and Space (ACAE) and the Costa Rica Institute of Technology (TEC). It also involves a variety of national and international stakeholders from government, academia, and industry. This paper is a continuation of previous reports on Irazú that were presented at the Workshop on Small Satellite Programs at the Service of Developing Countries over the last five International Astronautical Congresses. The project has already reached major milestones, such as the approval of the final design presented in the Critical Design Review (CDR), successful assembly of the manufactured structure and the components received from different CubeSat component providers, and successful performance during various environmental tests. The mission and satellite system architecture for a CS&F system were defined, which included the three primary components: the remote station, the spacecraft, and the ground segment. Experts from the National Aeronautics and Space Administration (NASA), Kyushu Institute of Technology (Kyutech) and Delft University of Technology (TU Delft) revised the design of Irazú. Advances in the Assembly, Integration & Testing (AI&T) phase are presented and discussed, which include the development of spacecraft components, testing of the communication link, assembly of the satellite and initial results of environmental testing. International cooperation is emphasized in this phase, because Costa Rican engineers carry out testing at the laboratories of the Kyushu Institute of Technology. Furthermore, advances in the satellite frequency coordination process and spacecraft registration for an emerging space nation are presented, as well as the lessons learned from the AI&T phase.@en