NASA and Boeing are ramping up their preparations to begin full-scale production of the first Space Launch System (SLS) Core Stage assembly. The schedule calls for the completion of the Exploration Mission -1 (EM-1) Core Stage in time to be shipped to the Stennis Space Center for a full stage test firing in 2017.
After being sidelined for repairs, the Vertical Assembly Center (VAC) is now expected to be handed over to Boeing around the end of October.
This machine is where the Cores and tankage for the SLS will be welded. However, it has been suffering from major teething issues.
The handover of the VAC and acceptance of the tool will allow assembly of the major structural elements for both flight and test articles to begin next year.
“From a broad picture standpoint, it’s continuing to do factory readiness through this year,” noted Patrick Whipps, NASA resident manager at MAF for the SLS Core Stage.
“(We will) complete that in early ’16 and begin to bring those structural test articles (STAs) and simulators to Marshall (Space Flight Center) in late ’16 or early ’17 at the latest.”
The Core Stage structural test articles consist of the major structural elements: the liquid oxygen and liquid hydrogen tanks, the engine section, the intertank, and the forward skirt. Those elements will be tested individually at Marshall, with MAF fabricating simulators of the elements that would normally be mated together.
“(The simulators) won’t look exactly like flight hardware, but their function is to test the center of gravity and some of the structural capability…in the (structural test) hardware,” added Mr. Whipps.
All of the welding tools at MAF are now up and running except for the Vertical Assembly Center (VAC), which is the tool responsible for the assembling of the barrels, rings, and domes into the complete Core Stage structures.
Despite being unveiled in a NASA fanfare, the machine suffered from a false start as the vertical rails of the VAC were found to be misaligned, which has kept the tool off-line ever since.
Realignment of the rails is now complete, but the slight position changes were significant enough that the software used with the tool had to be updated.
“Recovery Decision Meetings” during the year have seen the handover date slip month on month, but it is now anticipated that the VAC will be turned over to Boeing sometime around the end of October for qualification and acceptance testing.
“From a qualification and acceptance perspective, there are four stages,” said Frank McCall, Boeing SLS Deputy Program Manager. “First is tool acceptance, and you’ll see by the VAC a big barrel on which we’ll do that tool acceptance weld. We’ve already made one weld on that barrel; we will re-weld that and weld another barrel to that and that will be the process by which we accept the tool.
“Then we have weld confidence articles, which are articles that actually qualify the weld process. So we’ll go weld flight-type hardware on weld confidence articles and then we’ll take those welds, excise them, and go do tests on the welds to ensure that the welds have the right integrity.”
In addition to the assembly of the structural elements, preparations for sub-assembly work to outfit the elements is also in progress. Mr. McCall noted that sub-assembly parts suppliers are currently qualification testing their components for delivery to MAF over the next several months and into early next year.
Similar in some respects to the Shuttle ET, the SLS Core Stage is more complicated.
“We’re making a rocket, not an External Tank here, but we’re making an External Tank and then making it a rocket,” Mr. Whipps noted.
Beyond the propellant tank functions, the Core Stage houses the SLS vehicle avionics in the forward skirt at the top, and the propulsion package in the engine section at the bottom.
“The engine section is by far the most complex new portion of the Core Stage…it will be as densely-packed as the (Space Shuttle) orbiter boat-tail ever was,” Mr. Whipps added.
The engine section includes structural elements for the RS-25 engines and the five-segment solid rocket boosters that are attached at their aft end. It also includes hydraulic, pneumatic, and electrical services for the engines and the vehicle.
“That area is being carefully (arranged), with ergonomic models involved just to be sure that we know how to get people in and around and tighten every bolt and inspect every joint.”
Concurrent with the STA testing at Marshall, MAF will be constructing and assembling the flight hardware for the first Core Stage, CS-1.
After the flight structures are assembled in the VAC, they will get a coating of primer and then the thermal protection system (TPS) foam application.
Following that process, the tanks will be integrated vertically with the other outfitted structures in two major sub-assemblies: the forward-skirt and the intertank with the liquid oxygen tank and the liquid hydrogen tank with the engine section.
External outfitting of the sub-assemblies with feedlines and system tunnels will occur after they are positioned horizontally in the final integration area before they are joined together to allow for final TPS closeouts and RS-25 engine installation.
The now full-assembled rocket will then undergo extensive functional checkouts.
The current schedule continues to call for final assembly and checkout to be completed and the stage ready for transport to the Stennis Space Center in September 2017.
The stage is expected to then ship to the Kennedy Space Center at the end of that year for mating inside the Vehicle Assembly Building (VAB).
(Images: Via Philip Sloss, NASA and L2 – including SLS renders from 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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