Hi Joe
On the whole the missions/objectives within OHII will become available when some conditions are met - i.e. pass or fail the last mission/objective.
On occasion however - there are date restrictions in place. Thus missions are only ready after a date.
You can check this by looking at post 2 in the main OHII thread.
If this is the case - you can either patrol/dock until date is passed and mission is read or just go out on patrol anywhere and you will get a radio message when the next mission is ready.