NASA

NASA

NASA

NASA

NASA

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."

A spokesperson from Marshall Space Flight Center, which is managing construction of the SLS rocket for NASA, said the stand down was needed to "perform an intensive site process review."

It is not clear what triggered the need for a corrective action, but one source suggested to Ars that Boeing technicians are having difficulty attaching the large rocket engines in a horizontal configuration rather than a vertical position. NASA and Boeing made a late change to the final assembly process, deciding to mate pieces of the core stage horizontally rather than vertically to save time. However, this source said horizontal mating of the engines has created problems.

Despite this, NASA officials said progress is being made. "NASA and Boeing are expected to have the first engine soft mated to the core stage next week," Tracy McMahan, a spokesperson for Marshall Space Flight Center, said on Saturday. "However, there are many steps in engine installation that have to occur before the installation is complete."

Nine years in

NASA is hoping to complete core stage assembly as soon as possible, which would allow the rocket to be moved by barge from Louisiana to a large test stand at nearby Stennis Space Center in southern Mississippi. There, at some point in 2020, the space agency plans to conduct a full-duration test firing known as a "Green Run" test to ensure the rocket is safe to launch.

This core stage is expected to fly the Artemis 1 mission for NASA some time in 2021, although the agency has not set a formal date yet for this flight after several delays.

Last week, in fact, marked the ninth anniversary of the SLS rocket program, which was created by a Congressional authorization bill in 2010. The rocket was originally supposed to be ready to launch by 2016. Before the rocket's first flight, NASA will have spent about $20 billion developing the SLS core stage, other elements of the rocket, and ground-support equipment.

One of the architects of the authorizing legislation, Alabama Senator Richard Shelby (R), has demanded that NASA use the SLS rocket to launch humans to the Moon, despite the availability of the Falcon Heavy, which costs significantly less and has already flown three times.

Listing image by NASA