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  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. However, after assembling the core stage structure in September, two sources familiar with Boeing's work at the factory said the company had to "stand down" operations due to some issues.

“Corrective action”

Now, NASA officials have provided a little information about the causes of the delay. In a statement, the space agency's headquarters told Ars that "NASA initiated a forward looking corrective action request focused on improving the production system in preparation for Core Stage 2 and beyond." As a result of this corrective action, which was not specified, "Boeing chose to stand down in some areas and ensure the whole production team was aware of the intent behind the corrective action request."