Five Solar Cycles of Solar Corona Investigations.

These are the memoirs of fifty years of research in solar physics, closely related to the history of three of the major solar space missions, from the Solar Maximum Mission, SMM, to Solar Orbiter, at present in navigation toward vantage points closer and closer to the Sun. My interest in solar physics was stimulated by the studies on cosmic rays at the University of Turin, and the research in this field initiated at Stanford University as a postdoctoral fellow in the team of John Wilcox with studies on the large-scale corona and its rotation. Thanks to Alan Gabriel, during my first space mission, SMM, I was involved in the operations and scientific data analysis of the Soft X-ray Polychromator. Together with Giancarlo Noci and Giuseppe Tondello, I participated in the realization of the UltraViolet Coronagraph Spectrometer, NASA/ASI, flown on-board SOHO. After this experience there was the opportunity to participate in the formulation of the proposal of the Solar Orbiter mission, and to guide the team, which for this mission developed the Metis coronagraph, up to the delivery of the instrument to the European Space Agency in 2017.

Stray-light analysis for the SCORE coronagraphs of HERSCHEL.

The HERSCHEL (Helium Resonance Scattering in the Corona and Heliosphere) suborbital mission scientific payload consists of two extreme ultraviolet (EUV) coronagraphs forming the SCORE (Sounding Coronagraph Experiment) and an EUV Sun disk imager. The mission will be of great importance for the investigation of solar wind dynamics by obtaining the first global image of the Sun (disk and corona) in the He ii30.4 nm line. The most stringent requirement for the optical design of a coronagraph is stray-light reduction. We summarize the stray-light analysis for the SCORE coronagraphs, which are characterized by an innovative optical design, optimized for stray-light reduction.

Optical design of a high-spatial-resolution extreme-ultraviolet spectroheliograph for the transition region.

A spectroheliograph dedicated to the observation of the solar disk in the extreme-ultraviolet OV spectral line at 62.97 nm is described. As demonstrated in the Skylab SO-82A spectroheliograph [Appl. Opt. 16, 870 (1977)], this line is uniquely suited to characterize solar plasma in the important 250, 000 K temperature regime. No multilayer coating or suitable filter is yet available to select this wavelength, so an optical design based on a double spectrograph with a spatial filter to remove the unwanted radiation has been developed. Analysis of the optical design shows that this instrument can obtain a 1 arcsec spatial resolution (two pixels) with a relatively high image-acquisition cadence. A preliminary tolerance analysis has been performed. A simple method of instrument alignment in visible light is also described.