The Collection tab in the LUNA Administrator allows you to manually set the order for the list of collections in the LUNA Library and LUNA Viewer.

Select the collection (click to highlight) and click "Edit Selected" to change the Sort Order number for a collection. The lowest number collection will appear first in the list in the LUNA Viewer. When you have all your collections in the proper order you will need to restart Luna 7 (tomcat) to have the changes take affect.