== Stupid mission description == 

 "The mission aims to compile a 3D space catalogue of approximately 1 billion stars, or roughly 1% of stars in the Milky Way" 

 Why 1 billion? Because the rest are too far out, so no parallax will be detectable? Because the rest are too faint, so Gaia won´t see them? How should anyone know it´ll be a billion, if most of them will be seen for the first time? Will the mission stop when it´s found a billion? 

 That is stupid ad-talk, aimed at people who are stupid. It´s not a mission target. Nobody will care if it gets 500 million or 2.5 billion stars.