2. Solar collectors

Of all optical sensors, solar collectors are the most widely used. This is mainly due to the intrinsic characteristics of the Sun, namely :

• its energetic radiation, equivalent to a luminance of 2 · 10 ⁷ W · m ^–2 · sr ^–1 or an average illuminance outside the atmosphere of 1,350 W · m ^–2 , which makes it possible to use simple, reliable equipment without detection problems due to an excessively low signal-to-noise ratio;

• its inertial galactic position and apparent angular diameter ("32' as seen from Earth), which greatly simplify attitude determination algorithms;

• its spectral emission, which is...