The Packmule, like many similar designs, is an automated system freighter created for the purpose of hauling materials that are not time or spoilage sensitive, such as volatiles and refined metals from distant worlds within a system.  Supply squadrons of six to twelve Packmules can maintain a regular supply of materials to the inner system worlds reliably and cheaply.  The AI is not particularly bright, but capable of effectively managing its vessel and its cargo under most circumstances.  Packmules can be found throughout Sagittarius, though most are flagged with the SDC supplying Ice Stations and Waystations with volatiles from icy bodies in the outer worlds.