Instructions
Get in a Republic Gunship, as it has the speed and firepower you need for the first part of the mission. Command everyone in the ship to get out.
Destroy the Techno-Union ships immediately, as they're both vulnerable to your gunship and capable of causing considerable damage if you ignore them. Use a combination of lasers and missions. Unleash everything you've got on them.
Track down the Spider Walkers, and finish them off next. As long as your Derelict isn't captured, continue to harass the Spider Walkers. If the Derelict is captured, return to it immediately, and fight off any nearby enemies. Free the Derelict, and continue.
Send your full force to the Spire to capture it. Make the Timuera Morrisons your main attackers, while the rest of your fleet focuses on defending them. When you capture the spire, you win the mission.