The SMOS satellite was launched on 2 November 2009. It consists of the platform and the payload, the SMOS instrument MIRAS, which is mounted on a standard 'spacecraft' platform called Proteus. The Proteus platform was developed by the French space agency CNES (Centre National d'Etudes Spatiales) and Alcatel Alenia Space. The platform acts as a service module accommodating all the subsystems that are required for the satellite to function.
Following launch, when the spacecraft was separated from the launcher, an automatic start-up sequence was initiated, which resulted in the deployment of two symmetrical solar arrays. A sun-synchronous, dawn-dusk orbit is required to obtain the optimum data on soil moisture and ocean salinity. The solar arrays will always be illuminated, except for short eclipse periods in winter.
Proteus uses a GPS receiver for orbit determination and control, which provides satellite position information, and a hydrazine monopropellant system for four 1-Newton thrusters that are mounted on the base of the spacecraft. Nominal attitude control is based on a gyro-stellar concept. The Star Tracker is accommodated on the payload and provides accurate attitude information for both the instrument measurements and the satellite attitude control. Three 2-axis gyroscopes are used to measure the change in the spacecraft orientation, and thus provide the accurate attitude knowledge needed to fulfil stability and pointing requirements. Four small reaction wheels generate torque for attitude adjustment. In safe mode, a less precise attitude is maintained using magnetic and solar measurements, namely with two 3-axis magnetometers and eight coarse Sun sensors, while magnetotorquers act as the only actuators.Mission details
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