The Mothership is en route to Hiigara, but is pulled out of hyperspace for the 3rd time. A large asteroid is on course with the Mothership with a huge (and I mean, huge) escort fleet comprising of 4 Destroyers, 20 Assault Frigates, and a large number of strike craft. As the Mothership's drives aren't functioning, all vessels are scrambled to take out the enemy forces. After destroying all enemy vessels and the Headshot Asteroid, they jump off to the Homeworld.
This can either be a very simple mission, or a very hard mission. For a start, don't hyperspace away from Mission 14 if you don't have at least 100 Ion Frigates (90 of them will be captured), 7 Destroyers (3 captured) and 4 Heavy Cruisers (1 captured). As soon as you gain control of the vessels, move your entire battle group to a point in front of the Mothership, then wait for a large X Formation of Interceptors. Take them out as fast as possible, then destroy the Broad Formation Multi-Gun Corvettes. Shortly after, there will be a large broad formation of Assault Frigates and Destroyers coming into sight, as well as a moderate sized X Formation of Assault Frigates. Take these out as fast as possible (losing ships will almost certainly happen), then move all vessels to the Asteroid. Once it has been destroyed, exit immediately.
Don't put ships on guard duty or formations. There's no point and you will likely lose the mission and many ships.
As soon as you start, send a proximity sensor towards the enemy: some of the ships will likely divert their attention to that instead of the Mothership, which means you can take out the Capital Ships easier.
Don't waste time at the end recuperating: you'll only end up being attacked by any remaining fighters/corvettes left on the map.