All right, I'll give it a tryG 15

To unlock this achievement you simply need to unlock one of the three objectives to earn a star for each of the training missions. You need only complete each training mission to receive one star and there are five missions:

Beggar's Canyon - Shoot down imperials in an X-Wing
Endor Chase - Chase down rebels on a Speeder Bike
Overpower - Take command of an AT-ST and eliminate the rebels
The Dark Side - Play as Darth Vader or The Emperor and clear the rebel base on Hoth
Invasion - Protect the rebel base on Hoth with your Snow Speeder