Pegasus trip to Marshall for SLS engine section STA

by Philip Sloss

As the facility continues repairs of tornado damaged infrastructure and looks to find workspace for displaced tenants, NASA, Space Launch System (SLS) Core Stage prime contractor Boeing, and facility operations and maintenance contractor Syncom Space Services are ready to ship the first SLS hardware element from the Michoud Assembly Facility (MAF) in New Orleans, Louisiana to start structural testing.

SLS Engine Section:

Assembly of the qualification or structural test article (STA) for the Core Stage engine section element was completed last week and it was moved onto NASA’s Pegasus barge on Thursday in preparation for a one to two-week trip to the Marshall Space Flight Center in Huntsville, Alabama.

The engine section is the bottom-most element of the Core Stage where four RS-25 engines are located on the flight article.

The STA is a version of the engine section outfitted just for structural testing.

It includes the primary structural elements of the flight article – the barrel, a welded ring at the forward end, and a thrust structure where the engines attach.

The ring was welded to the top of the barrel in the Vertical Assembly Center in March of last year and then the article was given a coat of primer to protect against corrosion.  It was then joined with the thrust structure in a structural assembly jig where about 2500 bolts were used to attach all of the structural elements.

Test instrumentation and wiring runs were also added to help measure how the article responds to being pushed, pulled, and twisted in the test stand at Marshall.  The STA was moved into Cell A in Building 110 at MAF at the end of March for stacking with a simulator.

“What would normally be on top of the engine section would be the liquid hydrogen tank,” Tim Flores, integration manager for the SLS Stages Element Office, said during a media event this week.

“Rather than duplicating [a hydrogen tank] for an engine section test, we build a simulator and that’s where we impart the loads – where we put the pushing and the pulling and the twisting [forces] on the engine section.”

While in Cell A, 360 bolts were used around the circumference of the engine section ring to bolt it to the simulator.  A non-flight spray-on foam insulation called Versa-Foam was also sprayed in the area of that bolted interface to help simulate the environmental conditions seen during flight.

“We’ve got foam on the inside and the outside and the reason that we do that is because, in the structural test, it has to see some of the environments that we will actually have,” Mr. Flores explained.

“So we will run liquid nitrogen through that interface, just as if it were a liquid hydrogen tank, but we use liquid nitrogen.  There’s tubes that go in and out of the foam on the inside, where the liquid nitrogen flows through.”

Stacking operations were completed on April 20 and the mated article was moved from Cell A to the nearby final assembly area in Building 103, Area 47-48.  Originally, the engine section STA was planned to be moved while oriented horizontally and using self-propelled modular transporters (SPMTs); however, the SPMTs are waiting for other hardware.

“We’ve done all the testing we can do,” Flores said regarding the SPMTs.  “We haven’t finished the site-acceptance test because, for the outdoor ones, we need the ground support equipment (GSE) which we don’t have yet.”

The GSE attaches the vehicle hardware to the SPMTs.

The engine section STA also includes structural elements for one of the two liquid oxygen feedlines (also called “downcomers”) that run along the outside of the Core Stage before entering the engine section.  Steve Doering, manager of the SLS Stages Element Office, explained that only one was necessary.

“We added the downcomer testing on that engine section a while ago and it’s symmetrical, so we’re doing the loads test on one side,” Mr. Doering said. “There’s no sense spending all that money to build another one on the other side just to get the same data.  From a structural standpoint you just need to do the one side.”

The approximately one-mile tow for the STA on its transporter from Building 103 to the dock at MAF where the Pegasus barge was waiting took less than an hour; loading took longer, due to tight tolerances of the vertically oriented assembly with Pegasus.

Originally built in 1999, Pegasus was used to transport Space Shuttle External Tanks from MAF to the Kennedy Space Center (and in a few cases, the reverse).

It was 260 feet long at the end of the Shuttle era, but SLS Core Stages are almost 60 feet longer than Shuttle tanks and much heavier, so a 115-foot section of the barge was removed and replaced with a 165 foot section designed to handle the higher cargo weight, bringing the overall length to 310 feet.

The route for the trip from MAF to Marshall is approximately 1240 miles, which is expected to take about 10-12 days.

Pegasus will be taken by tugboat on a route first up the Gulf Intracoastal Waterway to the Mississippi River, then the Ohio River, then the Tennessee River.

“In inland waters, we have one tug towing and one pushing,” Pegasus Captain Terry Fitzgerald explained, “just because of the size and the visibility issues with the operators of the tugs.  So we have one towing, which is basically propelling us through the water and we have an aft tug that is controlling the barge.”

Fitzgerald, who is with Syncom Space Services, will lead a crew of six NASA and contractor personnel that will stay on the barge during the trip.

“We have a lot of conditions that we have to look at – we’re constantly monitoring vertical clearances, river heights, it’s an effort from both the tug crews and the on-board crews,” he said.  “We will be standing watches – they’ll be doing watches 24 hours while we’re on-board.”

Fitzgerald has served on Pegasus since 2009 across NASA contractors and helped ferry the last Shuttle tanks to Florida.

At the Marshall harbor, the STA will be taken off the barge and towed about six miles to the space center where the engine section test stand is set up in Building 4619.

“It’ll spend about a week outside of the test structure.  After we’ve prepped it, we’ll put it in the test stand,  we’ll connect up all the hydraulic load lines which is the way we put the loads on engine section.

“We’ll connect up all the instrumentation – we’ve got about 3000 channels of different types of instrumentation that we’re going to be monitoring.”

In addition to that work, Flores said the test stand will be brought around the STA to enclose it during the four-months of test preparations.  “We’ll have it open [when the STA arrives], we’ll pull in the test article, and then we’ll build up the test facility around it.”

The test program itself will be about four months.  “We should be starting in the late Fall, that puts it in the October time-frame and that should take us into early next year,” Mr. Flores added.

Keith Hefner was in his second day on the job as the new director of MAF when the tornado hit the facility on February 7.  During the media event, he provided an update on the impact of the tornado and overall recovery efforts.

Current estimates are that the tornado caused damages of approximately $300 million, with the largest impact to one of MAF’s largest tenants, the U.S. Department of Agriculture’s National Finance Center (NFC).

The NFC was in Building 350 across the street from the NASA SLS factory and assembly areas; although fortunately no one was seriously injured, the tornado displaced the 1300 workers in Building 350, which is now uninhabitable. MAF is working to find office space for all the NFC workers.

“We’ve got a hundred of those 1300 employees back in Building 101 – we had some vacant office space there,” Mr. Hefner noted.  “We’ll have office space in that same building to accommodate about 500-550 more.  So about half of the 1300 employees we’ll have in Building 101 within the next six to…eight weeks on the outside [of the estimate].”

“For the balance of the employees, we’re looking at bringing in modular offices onto our campus here and we hope to have that in place…within the next three to four months.”

Hefner said that there are ongoing discussions with the different federal executive and legislative branch stakeholders about a more permanent solution.

Repairs to the facility continue, and even as the engine section STA was rolled out of Building 103 on Thursday workers were busy repairing sections of the roof nearby.

(Images: NASA and Philip Sloss via L2 which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. SLS render by L2 Artist Nathan Koga. The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*))

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