Launching a satellite seems fairly simple: put it onto a rocket and launch it into space. Of course it's a bit more complicated than this and some missions are more complex than others. In the case of Gaia we have to launch at a very specific time each day. This lift-off time is determined by the Libration Point Mission Analysis Group of ESOC. In this blog entry I'll explain why this launch time is so constrained and how we determine the exact lift-off time.
There are three major factors that contribute to this launch:
- The destination of Gaia, the Sun-Earth libration point, or Lagrange point 2
- The programming of the Soyuz-Fregat launcher, the so-called Flight Program
- The movement of the Earth around the Sun and the 23.5º tilted rotation axis of the Earth with respect to the ecliptic plane
Let's first have a look at where Gaia is supposed to fly to. This is an orbit around the Sun-Earth Libration Point 2 (SEL2). The SEL2 is located about 1.5 million km behind the Earth, when looking at the Earth from the Sun. It lies in the ecliptic plane, this is the plane in which the Earth moves ...