ON THE ORBIT SELECTION OF THE SPACE SOLAR TELESCOPE ADAHELI

ADAHELI (ADvanced Astronomy for HELIophysics) is a project of the Italian Space Agency to carry out a small mission on the investigation of solar photo-spheric and chromospheric dynamics, via high-resolution spectro-polarimetric observations in the near-infrared spectral range. In the frame of the ADAHELI project, the present study deals with the orbit selection in order to satisfy the mission requirements. The main driver, in searching the suitable orbit, is the doppler shift that affects the orbiting telescope and which has to be kept within required bounds. Three groups of orbits are analyzed: Sun-Synchronous Circular Orbits, Sun-Synchronous Frozen Elliptical Orbits and Frozen Elliptical Orbits. To compare these orbits, two parameters must be considered based on the mission requirements of the time percentage of continuous observations in the admissible doppler shift ranges.