New high resolution observations of the solar diameter from space and ground with the microsatellite program PICARD

The PICARD microsatellite mission will provide 2 to 6 years simultaneous me asurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities. The 100 kg satellite has a 40 kg payload consisting of 3 instruments which will provid e an absolute measure (better than 10 milliarcsec) of the diameter and the solar shape, a measure of total solar irradiance, and UV and visible flux i n selected wavelength bands. Now in Phase B, PICARD is expected to be launc hed before mid-2003. The engineering model of the diameter telescope will b e used on ground simultaneously with the satellite to investigate the atmos pheric bias and state on the possible accuracy of the ground measurements c arried up to now. We review the scientific goals linked to the diameter mea surement, present the payload, and give a brief overview of the program asp ects.