Modeling and simulation of the attitude dynamics and control of a multi-module satellite

5 Introduction In the scientific field, as far as Earth Observation is concerned, Synthetic Aperture Radar (SAR) is one of the most powerful solutions, since it allows to achieve high quality scientific results and has a wide range of applications. Nonetheless, SAR is very complex. Furthermore, It demands great resources on a satellite (size, power, cost) and this is the reason why SAR is mainly associated with big, expensive and institutional or military satellites. A possible solution is developing a FMCW (Frequency-modulated continuous- wave) technology. In this case, radar signal is continuous, not a pulse. A such radar needs less power, even though two antennas are necessary. Power decrease allows this configuration to be installed on smaller spacecrafts. However, the problem of having two antennas has to be solved anyway. This problem can be faced in two ways:  First chance is to operate on the SAR by using an intermediate technology, the iFMCW (intermitted Frequency-modulated continuous- wave), which is in the middle between a continuous signal and a pulse. With a continuous signal, an antenna sends a signal for the whole cycle (100% of the cycle), while with a pulse an antenna sends a signal only for a fraction of the cycle (for instance 10% ). When using iFMCW technology, the antenna instead sends signal for a higher percentage than a pulse, but lower than a continuous signal (for instance 50% of the cycle).  Second chance is to operate on the satellite architecture. It can be designed to embark the two antennas that are necessary. The SSBV Aerospace and Technology Group has proposed an innovative solution, using a combination of the technologies just mentioned and a modular architecture. It intends to develop a smallsat miniSAR, through the use of low- power SAR principles (FMCW and iFMCW). [1] A smallsat miniSAR represents a new low-cost solution for using SAR in space. The miniSAR main objective is