SUN OBSERVATION WITH A MICRO SATELLITE: THE PICARD PROJECT

摘要

This mission is named after Jean Picard (1620-1682), aFrench astronomer of the 17th century who achieved thefirst precise measurements of the sun diameter. Therecent analysis of these results obtained during theMaunder Minimum (a period where sunspots becamevery rare, which is also characterized by an intense coldclimate of the Earth) showed an increase of the solardiameter with respect to its present value. This resultopened the discussion of the solar activity dependenceon the diameter and pointed out potential relationshipbetween solar activity and climate variations.PICARD mission will make precise measurements ofdifferent global sun parameters such as diameter, solarshape, oscillation modes, and total and spectralirradiance, as a contribution to our understanding of thesun functioning. It intends to contribute to theidentification of the sun influence on global climatechanges.PICARD is the third of CNES micro satellite scientificmissions after the successful DEMETER andPARASOL missions. It is developed in partnership withthe scientific laboratories CNRS /Service d'Aéronomiefrom France, IRMB from Belgium and PMOD fromSwitzerland.This article covers all the aspects of the mission:scientific objectives, mission presentation, system andsatellite and payload description.Mission requirements are drastic: sun diametervariations should be measured with a precision of 2milliarcseconds (mas) over the mission duration, whichimplies a high level of stability and high pointingperformances. This paper will describe some of themajor technical challenges and associated solutions,implemented in the frame of a low cost mission.This paper then describes how PICARD takesadvantage of the existing MYRIADE micro satelliteproduct line and what accommodations have to beperformed from generic products.