The 3-STAR program is the new cubesat educational project at the Politecnico di Torino. It has been thought in response to the GEOID call for proposals issued by the Education Office of the European Space Agency. The GEOID (GENSO Experimental Orbital Initial Demonstration) initiative wants to settle an orbiting constellation of cubesats to be operated by the GENSO (Global Educational Network for Satellite Operations) ground-stations network. GEOID is expected to be the communication backbone of the initial version of the HUMSAT system. The main goal of HUMSAT is to use the constellation of satellites and the GENSO ground stations, to provide support for humanitarian initiatives, especially in developing areas or areas without infrastructure. The 3-STAR will be one of the nine cubesats in the GEOID constellation. It will be a 3U cubesat derived from the e-st@r cubesat experience. In addition, it will carry two payloads: the HumSat payload, consisting of a simple but extremely reliable communication module compatible with the elements of the HUMSAT system, and the P-GRESSION (Payload for GNSS remote sensing and signal detection) payload. The P-GRESSION payload aims at performing measurements by means of radio-occultation technique and scattering theory, using GNSS signals. In this paper the 3-STAR project is described together with a preliminary assessment on the performances of the GEOID/HUMSAT constellation. The main requirements of the GEOID/HUMSAT project have been used to drive an optimization process aimed at determining the best configurations of a swarm-like constellation of cubesats. The mission scenario is made of the nine GEOID cubesats, a number of GENSO ground nodes and several sensors distributed on the Earth surface. The results of the analysis demonstrate that the aspects related to the cubesat-system design cannot be decoupled from the design of the constellation, not even in a preliminary phase. Further, it is demonstrated that the performances of a swarm-like constellation are comparable to those of a well-distributed on
