The Space instrument SODISM and the Ground instrument SODISM II

PICARD is a French space scientific mission. Its objectives are the study of the origin of the solar variability and the study of the relations between the Sun and the Earth's climate. The launch is scheduled for 2010 on a Sun Synchronous Orbit at 725 km altitude. The mission lifetime is two years, however that can be extended to three years. The payload consists of two absolute radiometers measuring the TSI (Total Solar Irradiance) and an imaging telescope to determine the solar diameter, the limb shape and asphericity. SOVAP (SOlar VAriability PICARD) is an absolute radiometer provided by the RMIB (Royal Meteorological Institute of Belgium) to measure the TSI. It also carries a bolometer used for increasing the TSI sampling and ageing control. PREMOS (PREcision MOnitoring Sensor) radiometer is provided by the PMOD/WRC (Physikalisch Meteorologisches Observatorium of Davos / World Radiation Center) to measure the TSI and the Spectral Solar Irradiance. SODISM (SOlar Diameter Imager and Surface Mapper), is an 11-cm Ritchey-Chr´etien imaging telescope developed at CNRS (Centre National de la Recherche Scientifique) by LATMOS (Laboratoire, ATmosphere, Milieux, Observations Spatiales) ex Service d'A´eronomie, associated with a 2Kx2K CCD (Charge-Coupled Device), taking solar images at five wavelengths. It carries a four-prism system to ensure a metrological control of the optics magnification. SODISM allows us to measure the solar diameter and shape with an accuracy of a few milliarcseconds, and to perform helioseismologic observations to probe the solar interior. In this article, we describe the space instrument SODISM and its thermo-elastic properties. We also present the PICARD payload data center and the ground instrument SODISM II which will observe together with the space instrument.