A satellite platform provides the support on which to mount instruments and the infrastructure for the mission such as power, communications to the ground and navigation. In this case, the SMOS instrument will be carried on a generic platform called ‘Proteus’, which was developed by the French space agency CNES and Thales Alenia Space.

The platform is small, occupying just one cubic metre and acts as a service module to accommodate all the systems required for the satellite to function. In launch configuration, the overall dimensions, including the SMOS instrument, fit into a cylinder 2.4 m high and 2.3 m in diameter. The satellite weighs a total of 658 kg, where the platform weighs 303 kg (including 28 kg of fuel) and the instrument accounts for 355 kg.

After launch, when the satellite has separated from the launcher, the platform’s two symmetrical solar arrays are deployed automatically. These arrays are covered with silicon cells to generate power. Each array is made up of four panels, measuring 1.5×0.8 m each. Since the orbit is Sun-synchronous, the solar arrays remain static.

Proteus uses a GPS receiver for orbit determination and control, which provides satellite position information. It has a hydrazine monopropellant system with four 1-Newton thrusters mounted on the base of the satellite.

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