Officials from NASA along with prime contractor Boeing formally signed off on the first assembly of the most complicated element of the civilian space agency’s Space Launch System (SLS) rocket. After a review of data from two months of functional testing at the Michoud Assembly Facility (MAF) in New Orleans, the engine section element of the first SLS Core Stage is complete and is now cleared to be mated to the rest of the vehicle.
Reaching this engine section milestone took much longer than original estimates, which complicated the schedule for the first SLS launch on Artemis 1. Early in 2019, with the finish line for the engine compartment not appearing to get closer, the final assembly sequence was rewritten to do the remainder of it horizontally.
Work on the upper “four-fifths” of the stage was released from its dependency on the engine section in the Spring, those pieces were bolted together in late May, and standalone work is mostly complete. In parallel, the engine section/boattail assembly was also relocated to the same Final Assembly area at MAF in early April to complete outfitting, connections, and checkouts.
The next step is to move the engine section and boattail to another building, rotate them from vertical to horizontal, and then come back for bolting to the aft end of the stage in the last “major join” in its assembly. Boeing continues to aim to complete the full stage in December and barge it to the Stennis Space Center in Mississippi for a full, integrated checkout and acceptance firing as part of the Green Run test campaign.
Engine section functional testing completed
Functional testing of the engine section and boattail started in mid-June after all of their hardware was installed. The elements are parked in Area 47/48, the SLS Final Assembly area of Building 103 at MAF, in a tool designed to facilitate the revised final assembly sequence, which put together the remaining big pieces of the stage in a horizontal orientation rather than a vertical/horizontal mix.
The engine section is the compartment at the bottom of the stage where the Main Propulsion System (MPS) elements come together to meet up with the different propellant, hydraulic, pneumatic and electric interfaces of four RS-25 engines. The boattail assembly is a tapered, structural extension on the bottom of the engine section which includes a downward-facing base shield that provides protection from the heat generated during launch and ascent.
(Photo Caption: The integrated engine section/boattail assembly surrounded by scaffolding at MAF on June 28. Additional scaffolding is installed on the inside to provide hands-on access and support for technicians without having to step on or put excessive weight on internal flight hardware. The internal and external access platforms and the controlled work area inside need to be taken apart and removed to allow the assembly to rotated over to horizontal to mate to the rest of the Core Stage.)
As with the forward skirt and intertank elements before, a “break of configuration” review is a standard decision point at the end of production of each element. The functional tests systematically activate and operate all components from sensors to computers to power units to valves to pumps.
“We just finished up a dry run review of the break of configuration package, so we will finish up functional testing in the engine section and then have our quote-unquote, formal, ‘break of configuration review,’” Terry McGee, Engine Section Engineering Manager for Boeing, said during an August 14 interview.
“We’ll have all the stakeholders involved in that review to say ‘yup, we’ve collected all the data that we meant to collect, the data looks good’ or there may be some anomalies with it, but it’s anomalies that we can live with, it’s not an anomaly in the hardware, but more in the way that the test equipment was measuring the data and so forth, but that’s planned for later this week.”
Testing was completed late on Thursday, August 22 and the review was held the next day. Late on Friday, August 23, the ‘go’ was given by NASA to Boeing to breakdown the functional test configuration and proceed into final preparations to mate of the engine section to the rest of the stage.
The SLS team at MAF is hoping to bookend the unofficial summer in the U.S. with the final mates of the stage; the other sections were joined over the Memorial Day weekend in late May and they want to begin the sequence of moves to bolt the engine section to the liquid hydrogen (LH2) tank and fully join the stage over Labor Day weekend. Testing of components in the thrust vector control (TVC)/hydraulic system finished later than forecast, but other pre-mate preparations continued and the goal is still to pick up the engine section/boattail assembly and move it at the end of the week, which is also the end of the month.
“Because we have had a few small delays in the completing of the functional test, we have had the opportunity to pull forward some of the small items that were in that window to work now, so even though functional test/break of configuration has slipped a couple of days from the original plan, we’re still holding to the [schedule],” Jonathan Looser, NASA SLS Core Stage Propulsion Lead, said on Thursday. “We still have work to do, and so there is some risk to that but that is still the plan and the goal for moving the engine section.”
(Photo Caption: The aft end of the LH2 tank and the -Z side of the engine section in the Final Assembly area at MAF in late May; thes