The SMOS satellite is constituted of:
- a PROTEUS platform (Plateforme Reconfigurable pour l'Observation, pour les Télécommunications et les Usages Scientifiques). This platform is designed for about 600 kg mass satellites at launch.
- a payload constituted of the SMOS instrument which is a Microwave Imaging Radiometer using Aperture Synthesis. SMOS consists of a central structure and three deployable arms, each of which has three segments. During launch, these arms are folded-up, but soon after separation from the launch vehicle they are gently deployed via a system of spring-operated motors and speed regulators.
SMOS was launched by one of the modified Russian Intercontinental Ballistic Missile (ICBM) Rockot launchers, which were decommissioned as a consequence of the Strategic Arms Reduction Treaty (START). Launch was from the Plesetsk Cosmodrome in northern Russia on 2 November 2009.