The role of space techniques in the understanding of solar variability

The unique advantages of space observations are recalled, and the difficulties in performing reliable measurements of solar variability from space are stressed. The elements of a strategy aimed at improving the accuracy of absolute as well as relative measurements are given. We show with more details how space observations are crucial in determining the causes, the amplitude and the previsions of solar variability. We show how they would permit to gain a better view of the solar interior, of the origin and of the effects of the solar magnetic field. Is the quiet Sun constant? Is the magnetic flux constant? The answer to these questions is likely to be given by space experiments. We state that the understanding of solar variability and its prediction is an extremely difficult and ambitious task which will take a long time. It is urgent that space agencies realize this and start as soon as possible a long term program for measuring the solar constant and the spectral irradiance in various spectral regimes.