IIRC, as you enter the reactor room , Wedge (rogue 1) goes ahead and takes out the "power regulator"
if he doesn't , cycle through the reactor's coponents and destroy it yourself.
Then cycle through the components again , until your MFD reads "Reactor Core"
switch to torpedoes , link them and fire away !
Whle vectoring out, an average speed of 85 will get you out safely !
good luck !
P.S. I 'm trully amaze that I've managed to remember all that details. It;s been so long since I've managed to blast it away ...