NASA Stennis wrapping up B-2 Stand activation for SLS Green Run testing

by Philip Sloss

Pathfinder now in the Spring, starting to practice for upcoming tests

With activation work almost complete, the team is transitioning into practicing the test sequences that will be performed on the first SLS Core Stage, Core Stage-1 (CS-1), after it is set up in the stand. “Our next major event, which is Pathfinder, is now scheduled for April 1st so that’s why we’re trying to get the LOX and hydrogen activation tests all finished and nailed down, because we have to pull that,” Maynard said.

“Now that we’re coming out of activation, we’ll start diving into training,” he added. “We’ll work with Boeing and other NASA engineers to start training. We’ve already been doing that during our cryo activation, that’s part of the activation is to kind of work out detailed operating procedures for when the vehicle [is here].”

“So a lot more practice, then we’ll run scenarios, you’ll run your fire drills and other scenarios and there will be all these exercises we’ll do in the TCC to keep everybody proficient before the vehicle shows up.”

A graphic showing the positions of the Core Stage and Pegasus barge relative to the stand for lift and installation into the B-2 stand. Credit: NASA.

The timing of the Green Run test campaign is being driven by assembly of CS-1 at the Michoud Assembly Facility (MAF) and by testing and verification of the Stage Controller avionics and software. The set of computer boxes and racks for the Stage Controller were recently installed on the stand.

“That arrived a couple of weeks ago and we’re actually in the process of final installation,” Maynard noted. “Those are actually on the stand, kind of split between Level 7 and Level 10, and they’re hooked into the control center.”

The Stage Controller was developed by Boeing and they delivered another set of the same avionics racks to Marshall early in the Fall.

“When you take the Core Stage to Stennis Space Center to go test it, essentially you have to build a ‘Kennedy Space Center in a box’ with all of the command and control capability to make sure that the rocket can be fueled, make sure it can do its test firing, that it can be safed, and that you can do all of the checkouts of the systems that you want to do before you go commit it to Kennedy Space Center,” Boeing’s Vice President and Program Manager for the Space Launch System (SLS), John Shannon said in an early October media teleconference.

Core Stage avionics boxes in development in the SITF at Marshall in August, 2017. The SITF is being used for development and testing of computer hardware and software for both the flight vehicle and ground support, such as Boeing’s Stage Controller. Credit: Philip Sloss for NSF/L2.

“At Marshall there is a lab, its acronym is SITF, the SLS Integration Test Facility,” Shannon explained. “We put all of the avionics boxes, all of the wiring harnesses, all of the systems that are in the Core Stage in this one giant room and it’s essentially an iron bird — it’s the vehicle without all the structure.”

“And we install the Stage Controller, all the ten racks and all of the twenty-one consoles and we just started powering it up last week,” Shannon said in early October. “The team that actually goes and executes the Green Run will begin going into that facility and they’ll be running that four-inch thick binder of procedures through the Stage Controller to go and execute the actions that they’ll be taking during the Green Run.”

The most visible practice work will be on the Core Stage Pathfinder, the full-scale model that replicates the weight and center of gravity of a flight stage. The article mimics the form and fit of the stage and few of its external protuberances; its purpose is to run through and checkout ground handling procedures at MAF, Stennis, and the Kennedy Space Center.

“Remember I told you there’s some special spools in there? We’ve got to get them out of the way or you can’t get the Pathfinder in,” Maynard noted. “But that’s just temporary stuff.”

When Pathfinder arrives, it will be rolled off the Pegasus transportation barge on the Multipurpose Transportation System (MPTS). From there, the mock-up will be used to practice lifting a Core Stage out of the ground support equipment, into the stand, and then back.

A graphic showing the configuration of the Core Stage attached to the Multipurpose Transportation System (MPTS). Hardware Interface Structures (HIS) attach from the stage to table-shaped multipurpose carriers (MPC). Self-propelled mobilized transporters (SPMT) roll underneath the MPCs and pick them up for ground transportation. Credit: NASA.

“Right now we’re planning to do at least three breakovers and installations all the way through the process,” Maynard said. “Basically remove from the HIS-es (Hardware Interface Structures), into the stand, out, back into the HIS-es and do that about three times.”

The stage is secured to carrier tables in the MPTS by a forward HIS on each of the forward SRB attach fittings and a common HIS on the aft end.

The crane for the stand was also upgraded during the B-2 renovation project. “[As] part of the restoration effort we went ahead and completely dismantled the crane, sent it out, and got it ‘refurb-ed.'” Maynard said. “The boom was extended by fifty feet and the capacity was increased by one-hundred thousand pounds.”

A second, mobile crane will assist with lifting the Pathfinder and eventually the flight stages while they are horizontal and orienting the hardware from horizontal to vertical and vice versa. “You’ll have your main derrick which is pretty much in a fixed position, eighty foot radius, and then we’ll have a trailing crane which will be provided by a contractor,” he noted.

A graphic from a procurement request showing how a mobile crane would assist the main crane in the B-2 stand with lift of the Pathfinder and flight Core Stages at Stennis. The trailing crane would attach to the aft end. Procurement of the mobile crane service for upcoming operations is currently suspended by the partial U.S. government shutdown. Credit: NASA.

“So basically you’ll come up out of the HIS, you’ll come up horizontally.”

A solicitation by Stennis for procurement of mobile crane services for the lift operations is currently suspended due to the ongoing NASA shutdown.

Initial part of the Green Run campaign

After Core Stage-1 arrives at Stennis from MAF for the Green Run campaign, it will go through the same breakover and lift as Pathfinder up into the stand; however, the first major Green Run test is the modal test of the stage. “We’ll put the vehicle in the stand and you’ll secure it into the stand because at some point you’ve got to let everybody go home,” Maynard said, referring to crews staffing the cranes.

“Then we’ll come back at some point and we’ll actually lift the vehicle up off the mounts about six, ten inches and disconnect everything from the vehicle in terms of relative to the facility with the exception of the crane. You’re just dead hanging from the crane and then they’ll have these stinger units that will actually do those impulses to the vehicle and collect the data.”

March, 2018, presentation slide to NAC HEO committee providing a graphical overview of the nine “tests” in the Core Stage Green Run campaign at Stennis Space Center. Credit: NASA.

After the modal test, the stage will once again be installed in the stand. Much of the rest of the half-year long Green Run campaign will be getting the stage ready for the Wet Dress Rehearsal (WDR) and the actual engine firing hot-fire test itself.

“The set up is going to take up most of your time,” Maynard said. “After the modal testing, they’ll hook up the umbilicals to the vehicle and then they’ll be testing like nobody’s business. They have got to check out every circuit, every sensor.”

The Wet Dress Rehearsal is a tanking/”fill and drain” test and is currently planned to be the first time an integrated Core Stage will be operated under cryogenic conditions. With the exception of a few Main Propulsion System (MPS) components, the only flight-proven hardware on the stage are the four RS-25 engines.

The WDR will be the first opportunity to see how the spray-on foam insulation (SOFI) on the outside handles a fill and drain cycle and how the avionics, software, MPS, and all the systems on the inside of the stage work with its super-cold propellants.

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