I had a really hard time getting the window on the same face as the rocket body. Is there a way to snap to face to make that easier?
https://www.youtube.com/watch?v=EoZY22v5kFI
This video is about snaping in blender. I used face and had to still rotate, with other little adjustments.
Use Snap to Face, Snap with Center or Median and Align rotation to Target. Have your window in Object Mode and move it to the surface. It will snap the Origin of your window to the surface. Here I deliberately moved the origin, so you can see it more clearly:
Make sure that you do not Apply the Rotation of your window, or it will snap like this:
