This one's pretty easy. After you've destroyed the AT-STs that are attacking the shuttles, quick go back into the city, stay on the right side of it (would be the left side on your way in in case you want to ignore the tie bombers for a bit), there's a lone AT-ST, just destroy him and pick up the powerup.
Battle is a pure form of expression. It is heart and discipline, reduced to movement and motion. In battle, the words are swept away, giving way to actions-- mercy, sacrifice, anger, fear. These are pure moments of expression.