NASA hopes to install the first of four space shuttle main engines on the SLS rocket this month. [credit: NASA ] Nearly a month ago, NASA announced that Boeing had assembled the core stage structure that forms the backbone of its Space Launch System rocket. This meant that all technicians needed to do to complete the full core stage was bolt on four space shuttle main engines and connect their plumbing. Completing the core stage at NASA's rocket factory, the Michoud Assembly Facility in Southern Louisiana, would represent a significant milestone for the program.