I just did everything I could to complete the campaign mission to free Earth from the Drengin and the precursor shield. The Drengin are destroyed, the Crusader is parked in the indicated hex. - now what? Although the dialog announced the Drengin had been destroyed (and they no longer show in the diplomacy screen).
Stupid to tear down and rebuild planetary improvements every turn.
Stupid such obscure requirements to win.
Really inadequate answers.