Jump across the pistons, but fall into the trp. Each door will open showing a turret. Take them out as soon as they open because killing one turret is easier than killing three at once. Portal upward in the third turret's room.
Get on top of the pipe to get on the top balcony. Drop down and knock over the turret you land on.
Do some flinging to get across onto the top bit.
Push the button to activate the rocket turret. When it lines it laser up with you, it will fire a single rocket. Use the to smash the glass and move on ahead.
Use portals to make the rocket turret see you and smash this bit of glass, and the tube that carries a cube. Use the cube to climb into the vents.