Shoot a portal in the room after the door, and then go back to the test chamber's entrance using the Unstationary Scaffold again. Place the other portal anywhere in the entrance and pass through.
Place the first portal in front of the vertical door, and fire the other where the High Energy Pellet is bouncing.
When the pellet is on the vertical door side, place the place portal as the previous next to the button, and then go quickly through the first portal.
Go to the button quickly and stay onto to keep the vertical door open. Wait for the pellet to reach the Catcher.
