It needs to be so big to provide shade. It is not a question of keeping Gaia cool, but of keeping it at a constant temperature for its entire mission. The Gaia sunshield is as essential as the instruments themselves. Without it, the spacecraft will not be able chart the position and movement of one thousand million stars in our Galaxy. The sunshield also carries solar panels to generate power to operate the spacecraft.
Why this shield is so big compared to Gaia?
It needs to be so big to provide shade. It is not a question of keeping Gaia cool, but of keeping it at a constant temperature for its entire mission. The Gaia sunshield is as essential as the instruments themselves. Without it, the spacecraft will not be able chart the position and movement of one thousand million stars in our Galaxy. The sunshield also carries solar panels to generate power to operate the spacecraft.