The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) instrument will be the first radiometer using aperture synthesis techniques for Earth observation. It will be boarded in the Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission of the European Space Agency and launched in 2005. The configuration under study in the MIRAS Demonstrator Pilot Project is a Y‐shaped array with 27 dual‐polarization L band antennas in each arm, spaced 0.89 wavelengths. In addition to these 81 antennas there are 3 additional ones between the arms for phase restoration and redundancy purposes and an extra one at the center of the Y array that is connected to a noise injection radiometer. The digitized in‐phase and quadrature outputs of each receiver are multiplexed in groups of four and optically transmitted to the hub where the complex cross correlations are computed. In this configuration there are 85 antennas‐receiving channels and 21 multiplexers. The objectives of this paper are twofold: (1) the study of the performance degradation of Y‐shaped aperture synthesis interferometric radiometers in case of single or multiple subsystem failures and (2) a reliability analysis at subsystem level.