GIMP Tool Box Move Tool.
Figure 1.1
Use the Move tool from the toolbox to position the Shuttle image. The Move tool's icon is made up of two crossed arrows. The GIMP indicates a tool is in use with a "grayed out" box as in the above image.
Select the /Dialogs/Layers to open the Layer dialog and click the Anchor icon to fix the selection to the Background in the active window.
NOTE: You can also click on the the active window's Background outside of the selection to fix it in place.