When the level starts, you will be in a dust cloud and told to keep ships inside of it. If a ship goes out, it will start a 40 second or so timer until the ship is back inside the dust cloud. When the timer is up, if there are any ships outside of the dust cloud the enemy will be informed of your position.

It is the best idea to destroy the right garrison first. To do so, you should build a mix of frigates and a lot of pulsar corvettes and travel through the dust cloud to the right side, it does not require elevation movement. Once it is destroyed, head back towards the mothership, and stop in front of the other ships.
Then, make sure you have a large force, with flak frigates (there will be a lot of fighters). Then move your force out of the dust cloud, just in front of your mothership. The purpose is to alert them of your presence, which will draw the other 2 garrisons toward you. They will not be hard to defeat if you have a good force.

Once the garrisons have been destroyed, you should rebuild your force, and then travel towards the oracle dig sight. there will be some things there that I recommend destroying before trying to dock the marine frigate. Once everything has been destroyed, bring in a marine frigate to dock on the dig sight and then you will complete the level!