need to get to the cannon from the lightning conductor but quick.

Climb down the ladder to the left of the machine. Turn left and exit the
workshop through the first door you come to. Defeat the two Opthalmicids
waiting outside. Head all the way down the fort stairs to the inner
courtyard. Defeat the two Photosauri there. Ignore the pathway through the
breach in the wall to the left. Turn right, into the arch and through the
door next to the chain box. Turn left and exit the planetarium through the
first door you come to. Defeat the two Shadow Zombies lurking in the
corridor. Enter the door to your right and into the Oubliette. Head down the
stairs and turn left at the bottom. You will find yourself at the cannon.
Backtrack all the way to the Lightning Conductor Shaft.

Practice this route again if you’re not fully comfortable with the run yet.
When you’ve memorized the route and you’re ready to go, start a new two minute
countdown on the machine and run as quickly as you can to the Oubliette and
down onto the cannon device. The run button is your best friend right now, so
keep your finger on it.

Once you arrive at the cannon, quickly access your inventory, select the
Photoelectric Pulsar and use it on the machine. Aline will hook up the device
just in time to have the Photoelectric Cannon destroy the wall in front of
her. From the explosion materializes a huge, scorpion-like creature. Arm one
of your stronger weapons and take out the Night Ripper.
Proceed ahead into the new opening.