Listening to some of the sounds in the AnnouncerAssault.uax package, it seems like AS-MotherShip was originally planned to have a few more objectives than the version that was released...
mothership_brief11: "Two more sentinels await you beyond the forcefield."
mothership_brief12: "Destroy these sentinels and the core blast door will be released."
mothership_brief13: "Once past the sentinels, proceed left or right to destroy the gravity generators."
mothership_brief14: "Paths once impassible are now clear."
mothership_brief11: "Two more sentinels await you beyond the forcefield."
mothership_brief12: "Destroy these sentinels and the core blast door will be released."
mothership_brief13: "Once past the sentinels, proceed left or right to destroy the gravity generators."
mothership_brief14: "Paths once impassible are now clear."