EGS Plan for the Pad: processing EM-1 hardware for launch

by Philip Sloss

The first integrated Orion and Space Launch System (SLS) vehicle that will launch Exploration Mission-1 (EM-1) will be put through a series of tests at the Kennedy Space Center (KSC) by NASA’s Exploration Ground Systems (EGS) processing teams beyond typical launch processing checkouts. Structural testing will be performed as major EM-1 hardware are joined for the first time in the Vehicle Assembly Building (VAB) and on the move out to Launch Pad 39B.

The EM-1 vehicle with its Mobile Launcher platform and umbilical tower will also make two trips to the pad, the first to run through a dress rehearsal of the launch countdown and perform first-time checkouts of the vehicle at the pad.

After returning to the VAB for inspections, late stow work, and final configurations, the vehicle will return to the pad for its first launch.

Processing and assembly

Processing the EM-1 hardware once it is turned over to EGS is divided between two teams. The Spacecraft and Offline Operations team processes Orion and SLS upper stage hardware, while the Integrated Operations team processes the SLS Solid Rocket Booster (SRB) and Core Stage hardware and assembles the whole vehicle on the Mobile Launcher (ML) in the Vehicle Assembly Building (VAB), starting with the SRB segments.

While Integrated Operations is stacking the SRBs on the ML and mating the Core Stage to them, the Spacecraft and Offline Ops team will be loading storable propellants and other commodities on Orion and the ICPS (Interim Cryogenic Propulsion Stage) upper stage. Orion will be mated with its Launch Abort System and trail the ICPS into the VAB.

After the motor segments loaded with solid propellant are offloaded from rail cars at KSC, they will be prepared for stacking together in the Rotation Processing and Surge Facility (RPSF) and moved one-by-one on a specialized transporter into High Bay 4 of the VAB. There each segment will be prepared for lifting into High Bay 3 where the Mobile Launcher is stationed for vehicle buildup.

The segments are also staged with equipment for mating operations in High Bay 4. “We’ll take it off [the transporter], move it over to the slap stand, prep the surfaces, and then we bring it up and over to High Bay 3,” David Diaz, Flow Manager for NASA EGS Integrated Operations, explained.

An inert aft assembly in build up stand, ‘384’ lifting beams, the VAB 325-ton crane, and an inert center segment sitting on a transportation pallet in High Bay 4 during practice sessions early this year. The flight booster segments will be staged for lifting and mating here. Credit: NASA/Kim Shiflett.

After the aft segments are put on the ML posts, the rest of the segments are connected at a tang/clevis field joint, with the bottom tang end of one cylinder lowered down onto the top clevis end of the other. The booster segments are physically fastened together with hundreds of pins around their circumference and then the field joint is closed out with cork and room temperature vulcanizer (RTV) to protect the joint from the outside environment before and during launch.

While the next segment is prepped in High Bay 4, the newly mated field joint will be then be leak checked. “What we use as criteria is as soon as we pass our joint leak checks, then we’re OK to go stack on the other side,” Diaz said.

Once enough segments are joined on the Mobile Launcher, workers will begin to start closeouts of the systems tunnel that runs the length of each booster. “It’s not going to be like ‘OK, I’ve stacked one, two, let’s go close out,'” he explained. “We’re going to find a nice place where we say ‘hey I think we’re stacked enough,’ we have an opportunity let’s go do us some systems tunnel closeouts at the bottom.”

“Then we’ll have an opportunity to move our lifts, I call it our scissor lifts up there and it helps us get through the platforms.  You have to go up almost 20 feet in some cases,” he added. The forward assemblies with the nose cone and avionics will complete the boosters at the top.

The SLS Core Stage will arrive by barge from the Stennis Space Center in Mississippi following its critical, half-year long Green Run test campaign there. The campaign will culminate in a 500-second, flight-duration test firing, and after refurbishment it will placed back on the Pegasus barge for the ocean trip to KSC.

After arrival, it will be rolled into the VAB and prepped for stacking with the two SRBs. “We are planning on installing some modal sensors for the modal test when we have that access available to us,” Jeffrey Angermeier, EGS Flow Director, said.

“Once we finish that and that will be in the Low Bay, we do our FTS (Flight Termination System) work in there with our linear shaped charges installed and we move it out. We do remove some hardware — we’ll put it up in the horizontal, there’s some hardware that we’ve got to go remove that came with the shipping, stuff that we’ve got to take off, but there’s no other work that I’m aware of, unless there’s some forward work coming to us.”

Structural dynamics testing with the first stack for the first launch

The Exploration programs, EGS, Orion, and SLS are still in major development, and EM-1 is a development test for all three. Above and beyond normal launch operations, a significant portion of the vehicle integration timeline has been set aside to prepare for and execute tests on the structural dynamics of the vehicle.

The programs have been collecting data on the structural dynamics of the different parts of the spacecraft and launch vehicle, in some cases with structural test articles being used primarily for loads testing. In other cases such as with the Core Stage, a modal test of the assembled flight stage will be run at Stennis at the beginning of the Green Run test campaign.

From a presentation to the NASA Advisory Council Human Exploration Committee earlier this year, three of the structural dynamics modal tests being performed prior to EM-1, a modal test of the Mobile Launcher by itself, the Partial Stack Modal Test (PSMT), and the Integrated Modal Test (IMT). Credit: NASA.

The modal data helps refine computer modeling of the vehicle will respond to the different forces it will experience in flight. “It’s a huge amount of effort that goes into characterizing these math models which are important to make sure we understand the loads during liftoff and ascent and also the flight control system,” Marshall Smith, NASA’s Director of Cross Program Systems Integration for Exploration Systems Development, said during a July, 2017, presentation to the Human Exploration Operations (HEO) committee of the NASA Advisory Council (NAC).

“Our GNC (Guidance Navigation and Control) needs to understand these modes and be able to understand what the accelerometers and rate gyros are telling it to do and that we understand and can separate that out from any flex dynamics that’s going on within the rocket.”

As the flight rocket is assembled in the VAB, two additional tests will be run at different points in stacking. Once the Core Stage is joined to the SRBs, a Partial Stack Modal Test (PSMT) will be run with the hardware isolated from Mobile Launcher umbilicals and VAB work platforms.

“That’s about a three, three and a half week effort to go in there and basically characterize the modal characteristics of the vehicle, with just the Boosters and the Core Stage,” Angermeier said. “We can’t have any access platforms in the vehicle, we have the flight doors on, there’s no umbilicals, that’s the configuration we’re at.”

The SLS Boosters and Core Stage will be heavily instrumented for the test and most of the time scheduled for the PSMT is devoted to getting set up to run the test cases. “It’s about three weeks of prep, hooking up the sensors and channelizing the sensors, and then about a week worth of testing,” he noted.

After the PSMT, the work platforms will be brought back around the vehicle, and the Core Stage umbilicals will be attached. Stacking will continue with the Launch Vehicle Stage Adapter (LVSA) being lifted into High Bay 3 and mated to the top of the Core Stage.

The Mobile Launcher umbilicals and connections for the SLS Block 1 Crew vehicle configuration that will fly on EM-1. These will be connected from the umbilical tower as the vehicle is stacked on the launch platform in the VAB. Credit: NASA.

The LVSA is bolted to the Core Stage and remains with it after the Orion and ICPS separate following powered flight. Three-hundred, sixty bolts around the circumference will join the bottom of the LVSA with the top of the forward skirt, and then the area will be closed out with spray-on foam insulation (SOFI).

“While we’re doing that foam closeout we can be stacking ICPS, the OSA, and Orion in parallel with that,” Angermeier noted. “We’re also doing umbilical connections, but there are a couple of umbilicals at the very top that we have to wait until we’re done with the LVSA foaming before we can basically attach the OSMU (Orion Service Module Umbilical) and the vehicle stabilizer.”

Orion final assembly, integrated testing

The Spacecraft and Offline Operations team will be working on the Orion vehicle elements while the Integrated Ops team builds up the SLS vehicle on the Mobile Launcher in the VAB.

The Orion Stage Adapter (OSA), which will carry thirteen cubesats, will be prepared and handed over for stacking separately from the spacecraft. “We’re responsible for processing, installing those, charging their batteries and getting them ready,” Lili Villarreal, Flow Manager for NASA EGS Spacecraft and Offline Operations, said of the cubesats.

After launch and Orion separation, the adapter will stay attached to the ICPS and the cubesats will be deployed in subsets across multiple deployment opportunities on the way to the Moon. During launch preparations, the OSA will be mated by itself to the ICPS.

Following structural connections between the launch abort tower and the crew module, the LAS ogive fairings are installed around the EFT-1 Orion vehicle in October, 2014. Credit: NASA/Kim Shiflett and Ben Smegelsky

The Orion spacecraft stack will move into the Launch Abort System Facility (LASF) after its flight commodities are loaded in the Multi-Payload Processing Facility (MPPF). “At the LASF our main goal is to install the LAS (Launch Abort System) and the ogive panels and so a lot of the work that we’re doing in the LASF is almost the same as what happened during EFT-1 (Exploration Flight Test-1), if you’re familiar with that flight,” Villareal said.

“There’s just a couple of minor technical differences in the ogive structure and how we do that, but we’ve had a lot of training sessions [on] how to put this thing together.”

The Motor Adapter Truss Assembly (MATA) of the already-assembled Launch Abort Tower will first be attached to the Orion Crew Module in the LASF, followed by the ogive-shaped fairing panels that cover it. “Once we install the LAS and do the technical testing for the post-installation then we’re pretty much ready to go to the VAB and turn it over,” Villareal said.

Orion in its launch configuration will be the last piece to be stacked. Similar to the PSMT, an Integrated Modal Test (IMT) will be performed after the full vehicle is stacked, but before getting into all the integrated testing and checkouts that need to be run before the vehicle is ready to go to the launch pad.

“After we get the vehicle completely integrated and we get all the umbilicals connected we do an initial power up, interface check between our ground system through the umbilicals with the launch vehicle and spacecraft — a couple-day test there just to verify we have good connectivity,” Angermeier explained.

“Once that’s done, we go through an umbilical retract test.  We have all the umbilicals attached to the vehicle and we’re looking for the timing associated with retracting, to make sure that they retract all at the same time.”

An artist concept of final stacking of the EM-1 vehicle, with the Orion spacecraft assembly lowered down on the ICPS. The current plan now has the Orion Stage Adapter (which houses the 13 cubesats) first being stacked separately on the ICPS and the rest of Orion being stacked on the OSA. Credit: NASA.

“Then we go into the series of optics work that we’ve got to do with the umbilicals retracted — there’s a bunch of engineering reference markings on the vehicle that we need to go make sure we know the precise location, because they will be used as engineering reference points during the separation events during the flight.”

“Once we’re done with that optical shoot, then we do the full-up vehicle integrated modal test,” he added. “[It’s] similar to the partial stack modal test, but it won’t take as long because a good many of the sensors we kept attached from the partial stack modal test.”

After the Integrated Modal Test, once again the Mobile Launcher umbilicals and swing arms will be reconnected to the vehicle and the team will go through integrated testing and checkouts. “We have about three or four weeks of integrated testing,” Angermeier noted.

Following integrated checkouts, the vehicle should be ready to roll out to the launch pad for the first time. An additional structural dynamics test called the Dynamic Rollout Test will be performed, collecting data on the small, vibrational movements of the vehicle and Mobile Launcher while Crawler Transporter 2 carries them from the VAB out to Launch Pad 39B for the first time.

Two trips to the launch pad, designed for shorter pad flow

The Mobile Launcher for SLS and Orion combines a launch platform and an umbilical tower; for the Space Shuttle, the tower and service structures were fixed on the launch pad, and vehicles typically spent at least three weeks at the pad prior to launch. For SLS, NASA’s goal is for only about one week at the pad before launch after rolling out of the VAB.

With all the vehicle umbilicals and connections mated in the VAB, most of the vehicle testing will also be done inside. “Because Shuttle was out at the pad for over a month, there [was] testing like FRT (Frequency Response Test) that they had us do when we were out at the pad. Our intent is to get all or most of that work done in the VAB and to keep our pad flow short,” Angermeier noted.

The plan is for the EM-1 vehicle to make two trips to the launch pad. The first trip is planned to last about two weeks, centered around a Wet Dress Rehearsal (WDR) test that will be the first opportunity to load cryogenic fuels on the launch vehicle at the pad.

An artist concept of the EM-1 vehicle and Mobile Launcher arriving at Pad 39B on Crawler-Transporter 2. Credit: NASA.

It will be the first time an operational SLS vehicle visits the pad and some additional testing will be done during this opportunity. “There are some unique tests that we’ve got to do the first time, it’s a matter of a day or two of tests, but for the most part, we get out there, we connect the ML to the pad, we get into some PSET (Program-Specific Engineering Test) activities,” Angermeier explained. “Those are program-specific tests for Orion and SLS — one-time tests they want us to go take a look at.”

The WDR is planned to go through launch countdown procedures and sequences, stopping prior to engine ignition. The test will also exercise safing, recycle, and scrub turnaround procedures, such as draining the vehicle.

Some of the preparations for the WDR are similar to launch countdown preparations. One of the major pad operations carried over from Shuttle is loading the SRB Hydraulic Power Units (HPUs) with hydrazine.

“The booster hydrazine servicing is the basically the same as we had for Shuttle,” Angermeier said. “For the boosters you had HPU carts that you would have that propellant in, you lift them up to the zero-level and you just service right from those carts.”

“Once we’re done with that, there is a comm (communications) and EMI (electromagnetic interference) test, that’s something that we do during Wet Dress that we don’t have to do prior to launch,” he added.

Following conclusion of the WDR test, the pad preparations will be reversed and the vehicle will be rolled back to the VAB. “We get into the Wet Dress Rehearsal, we deservice our hydrazine, and we come back into the Vehicle Assembly Building after that,” he said. “All that work takes us about two weeks.”

Pad 39B reverted back to the Saturn-era clean pad after Shuttle, and there is less maintenance and servicing infrastructure for the vehicle at the pad and less access to it there. In between the WDR and the launch countdown, vehicle servicing will be performed in the VAB.

The Core Stage tanks will go through another set of pressurization cycles during the WDR and the VAB work platforms will provide access to do a full inspection of the vehicle, including the Core Stage TPS (Thermal Protection System). “From the time we get back from Wet Dress until we roll out for launch we have about a week and a half, that is what our estimate today,” Angermeier noted.

“Some of the significant work that we’ve got to do, we’ve got to install flight batteries for the boosters, for Core Stage, for ICPS — those are both for vehicle avionics and for flight termination systems. We go through our ordnance ops, we do our end-to-end test.”

“We have a lot of the sensors that we installed for Wet Dress and for the Dynamic Rollout Test, we had a lot of sensors installed, we’ve got to remove those,” he added. “And then you already mentioned we’ve got to do an inspection of the entire vehicle and make sure we didn’t have any issues during the Wet Dress.”

For the uncrewed EM-1 flight, late stow items that will fly in Orion’s crew module will be installed in the VAB. “At launch minus fifteen days is our plan to stow all these payloads, and there’s a list of them,” Villareal said. “And then obviously when we do roll out to the pad there’s some final internal configurations that we’ve got to do in preparations for flight, but they’re all very minimal and all part of the launch countdown.”

The vehicle will then roll out to the pad for the one week pad flow for launch. Angermeier said the basic steps are similar to the first trip: “Same thing, we’ve got to connect the ML to the pad, make sure we’ve got all the facility connections hooked up, we do set up PSETs that we do with the vehicle just to make sure that it’s ready to go fly.”

Similarly, the booster HPUs will be reserviced. “Service hydrazine, we have Orion ordnance, basically the arming of the LAS ordnance that we had to do in the VAB, and then we get into our launch countdown,” Angermeier said. “And the entire time while we’re doing that, we’re working on different, various preparations to make sure that the pad is ready for flight once you get into launch countdown.”

The two-day long launch countdown would take up the end of the week’s time. “It’s about two days long, we go execute that test,” he said.

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