Proba-3 is such an ambitious mission that it needs more than one single spacecraft to succeed.
In order for Proba-3’s Coronagraph spacecraft observe the Sun’s faint surrounding atmosphere, the disk-bearing Occulter spacecraft must block out the fiery solar disk. This means Proba-3’s Occulter ends up facing the Sun continuously, making it a valuable platform for science in its own right.
The sunward side of the Occulter therefore hosts a dedicated instrument that will maintain a continuous measurement of the Sun’s total energy output, known as the total solar irradiance, which is a essential variable for climate studies.