Following verification and validation (V&V) testing in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) in Florida, NASA’s Exploration Ground Systems (EGS) Program has rolled Mobile Launcher-1 (ML-1) from High Bay 3 of the VAB out to Launch Pad 39B for a Summer of testing in preparation for the Artemis 1 launch. The rollout began on Thursday, arriving at 39B, ahead of a slight weather delay to get to hard down on the mounts on Friday.
Installation and checkout of systems on the mobile umbilical tower and launch platform is nearing completion and the tests at Pad 39B will verify that they are ready to support their first pad flow with NASA’s Space Launch System (SLS) rocket and Orion spacecraft.
The scheduled three-month long stay at the pad includes demonstration tests of countdown activities in and around launch day including propellant loading, sound suppression water system flows, and vehicle servicing.
The next planned trip to the launch pad for the Mobile Launcher (ML) would be with the Artemis 1 vehicle for a full launch dress rehearsal. In addition to validating that the ML and the Pad systems work together as required, EGS will practice running through other countdown timelines, such as securing the ML and the pad area ahead of propellant loading operations.
After the upcoming round of testing at the pad, the ML will be rolled back to the VAB to complete work ahead of formally being turned over to ground operations to begin vehicle integration. A few more tests in the VAB and a certification review are necessary to complete ML construction.
Final VAB testing completed ahead of rollout
“We’re rolling out to the pad June 27th, ‘triple balls one’ (0001 local time, 0401 UTC) on the 27th,” Cliff Lanham, EGS Senior Project Manager for the Mobile Launcher, said in a June 10 interview. Crawler Transporter-2 (CT-2) will pick up the ML in the VAB for the four-mile drive out to the pad.
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CT-2 took the ML out to Pad 39B from its East Park Site construction area for fit checks last September.
The ML was then rolled into High Bay 3 of the VAB for the first round of Multi-Element Verfication and Validation (MEV&V) work, which included additional installations and systems checkouts with Launch Complex 39 (LC-39) infrastructure in the assembly building and Firing Rooms in the Launch Control Center.
(Photo Caption: The Core Stage Engine Service Platform (center), with railings for the four RS-25 engines, is raised into its work position on the deck of Mobile Launcher-1 during pre-rollout testing and checkouts in mid-June. The two, large Tail Service Mast Umbilical assemblies to the left will plug into the engine section of the Core Stage. Two sets of four Vehicle Support Posts (middle foreground, middle background) indicate where the two SLS Solid Rocket Boosters will flank the liquid sustainer stage when the vehicle is assembled on the ML. On the periphery in this image, three of the Sound Suppression water “rainbirds” can be seen.)
Over the past few weeks, the ML-1 construction team has been wrapping up pre-rollout MEV&V work. Retract and drop testing of the arms that connect umbilicals to Orion and SLS was in work, along with checkouts of electrical, hydraulic, and pneumatic systems. Other work included installations of Sound Suppression water equipment on the ML and testing of hazardous gas detection and environment control systems (ECS).
In addition, development testing was also worked on the overnight shift where modal testing was performed. Modal tests are being conducted to collect data on the structural dynamics of the ML by itself, which can be used with data from future modal testing to be conducted after the Artemis 1 vehicle is assembled on the ML.
Service platforms for the aft-end of the two SLS Solid Rocket Boosters (SRB) and the four Core Stage RS-25 engines were also recently raised into the flame hole in the ML’s launch platform. These will allow technicians hands-on access to the rocket engines and nearby support equipment like the Booster thrust vector control (TVC) systems.
Additional data will be collected on system behavior and performance during the rollout on the crawler-transporter. “On the way out we’ll be essentially capturing the vibrations of the system as we roll out,” Lanhan said.
(Photo Caption: The liquid hydrogen (LH2) Tail Service Mast Umbilical arm is extended just prior to a retract test in the VAB in late June prior to rollout.)
“It’s a dynamic check of how things are reacting during the actual roll. So we’ll be checking that for both the base and tower of the Mobile Launcher, we’ll be capturing that. There’s some ECS testing, Environmental Control System testing, we’ll be doing as we roll out.”
“So we’ll be checking a few things as we roll out and then obviously once we get there we’ll set down, get hooked up, and then we get into our whole pad flow of testing,” he added.
The rollout of ML-1 comes on the heels of the construction award for a second ML. NASA announced the selection of Bechtel National, Inc. on June 25 to design and build Mobile Launcher-2 (ML-2), which was started by Congress with appropriations in March, 2018, to separate SLS and EGS development work on the SLS Block 1B vehicle from both ML-1 and the initial Exploration (now Artemis) Mission manifest that will use the Block 1 vehicle.
The 44-month contract period for ML-2 begins on July 1.
Pad testing campaign
One of the first things to test with the ML set down and hooked up to the pad is the Ignition Over-Pressure / Sound Suppression (IOP/SS) water system. “Basically that’s going to be four individual tests with a total of nine water flows out there,” Lanham noted.
Several water flows have been conducted at the pad without the ML, but the upcoming tests will verify joint ML-Pad operations.
“That’s one of the very first things that we want to get done out there is that first set of flows because we’re not sure, depending on the test data, whether we’ve got to change the orifice plates that are in the rainbirds and also on the pad side to get the flows right. So that’s going to be important to get that performed right away.”
(Photo Caption: Eight of the IOP/SS nozzles (top left) for the Core Stage engines can be seen in this image at the mouth of the ML flame hole; there are an additional eight nozzles on the other side of the flame hole for the liquid engines and twelve more for the SRBs, six each. The Core Stage Engine Service Platform is in the foreground in this image prior to being lifted.)
Other tests will demonstrate the combined performance of other water systems. “We’ll be doing fire suppression testing where we’re checking our fire suppression systems as well as our emergency egress system and our washdown systems,” he said.
The propellant systems from the cryogenic spheres in the storage areas near the pad perimeter will also be tested with the cross-country lines that run up to the ML. The super-cold liquids will flow through the ML’s liquid oxygen (LOX/LO2) and liquid hydrogen (LH2) lines up close to the connection points for the SLS Core Stage in Tail Service Mast Umbilicals (TSMU) on the deck of the launch platform and the Interim Cryogenic Propulsion Stage Umbilical (ICPSU) up on the umbilical tower for the upper stage.
“We’ll flow the LO2, LH2 from the storage areas up through the ML to both the Core Stage area and the TSMUs and also up to the Level 200 where the second stage will be and that’s where we’ll flow up to with the cryos,” Lanham said.
Additional testing will be performed when the Artemis 1 vehicle visits the pad ahead of launch, but these first tests without the vehicle can check out all the plumbing up to the last few feet to the vehicle, initial flows through the system, and also exercise the hazardous gas detection system to look for leaks. The propellant then has to be turned around to exit, which is a little different than with a vehicle in place.
“What we’re doing is we’re putting in what we call the ‘bathtub’ which is the low point I’d say inside the Tail Service Mast Umbilical and then we’ll actually have a tool that will flow and turn the commodity around and flow back out,” Lanham explained. “So we don’t actually go out to the end of the plates here and also we don’t have a vehicle so obviously we’re not going there, but we do have a turnaround tool that we’ll be using.”
Lanham noted that the venting and exit legs will also be tested. After the cryos get to the turnaround tools, the liquid oxygen will exit the ML and be dumped to the pad’s oxygen pond area and the liquid hydrogen will go out to the new hydrogen separator to allow it to boil off to a gas before it is burned in the pad’s flare stack.
In contrast to the Space Shuttle, the SLS Core Stage MPS does not recirculate the liquid hydrogen bleed coming off the RS-25 engines during the chilldown process. While the LH2 and LOX propellants are loaded into the stage’s tanks, a smaller amount branches off to flow through parts of the engines to thermally condition them ahead of startup; in Shuttle, the LH2 was then routed by pumps in the orbiter to a small recirculation line running from the aft compartment into the External Tank.
The SLS Core Stage deleted those hydrogen recirculation pumps from its MPS design and the LH2 engine bleed is dumped from the vehicle, running out of the aft compartment to a port on the LH2 TSMU and then away from the ML. The hydrogen separator was added to the pad vent system to provide a place for any liquid hydrogen to warm up and become hydrogen gas before it reaches the flare stack.
(Photo Caption: The LH2 propellant loading and vent lines can be seen in this drone image taken last August when ML-1 was at Pad 39B for a fit check. The lines run in between one of the pad lightning towers and the shorter pad water tower. Cross-country lines run from right to left from the LH2 storage (out of shot, middle right) to the ML. Vent and dump lines run left to right and the dark grey hydrogen separator can be seen about even with the water tower. Farther to the right is the hydrogen flare stack that will burn off hydrogen gas vented from the two SLS liquid propellant stages.)
Lanham went through some of the other tests at the pad: “We also have an integrated power demand and outage test where we check the capability of our power systems to satisfy the consumption that all of the subsystems are going to have when they’re active and the facilities, so we’ll do that,” he said.
“We’ll also be doing a CAA (Crew Access Arm) swing test out there. We have some SCAPE (Self-Contained Atmospheric Protective Ensemble) demos that’ll be done, so that’s all kind of a launch prep demo testing. And then we also have some end-to-end electrical testing that we’ll be doing as well for a few systems.”
“There’s also what we’re calling a launch prep demo test where we’ll look at the different activities that get you into a launch prep, like elevator securing, handling and access removal, pressurization of the ML, CAA (Crew Access Arm) closeouts, that type of stuff,” Lanham added. The EGS launch team will take part in those Integrated System Verification and Validation events to practice that part of the countdown timeline prior to the start of propellant loading.
There will also be some other work done out at the pad along with the MEV&V. “There will be some what I would call ‘punch list’ items that remain from the installation and the construction work, so we’ll be doing punch list items,” Lanham said.
“We do have just a little bit of structural work that we’ve got to complete that we won’t finish in the VAB that we’re going to finish up at the pad. Things like painting and architectural finishes, where we’ve got to put like acoustic tile in the electrical rooms, that type of stuff will be finalized. Really ‘cats and dogs’ types of stuff that we’ll have to finish up, including all the other testing at the pad, MEVV testing.”
Turnover to operations back in the VAB
After returning to the VAB from the pad, a few more tests will be conducted along with formal reviews to certify the ML is complete and ready to support its first launch.
“There is a couple of end-to-end tests that we have to complete once we get back to the VAB and also the booster stacking demo we’re going to do when we come back to the VAB, so we’ll do that in October, and then we go through the whole paper process of certifying the designs and all the systems,” Lanham said. “At that point we turn it over to operations and then operations will pick up with their work, which is the stacking of the vehicle.”
The booster stacking exercise will use inert, test hardware as in similar booster stacking practice that has occurred in the past in VAB High Bay 4.
“They’ll do the aft segment and I think a middle segment. [They will] practice making sure they can interface properly and get all their numbers and everything as they put the aft segment onto the Vehicle Support Posts on the Mobile Launcher and then I think they’re going to stack one more segment. And they’ll train their teams with that multiple times and they’re going to do both sides, the left and right sides of the Mobile Launcher with that, but they’re not stacking an entire booster.”
(Photo Caption: Some of the inert SLS SRB hardware in High Bay 4 of the VAB early in 2018. At the time, the aft segment (left) and the center segment were used to practice final pre-stack preparations. After ML-1 returns to VAB High Bay 3 in the Fall, the hardware will also be used to practice lifting the segments into the SLS integration cell. The EGS integration team will practice mounting the aft segment to both the left and right sets of ML Vehicle Support Posts and also lifting the center segment and stacking it on top of the aft segment.)
The Core Stage Pathfinder, a full-scale replica that has the same weight and balance of a flight article along with much of the form and fit, was still planned to be transported to KSC for fit checks. The passive article is currently at the Stennis Space Center for fit checks there. Lanham said that the current plan was that testing at KSC with the Pathfinder would be something conducted after the ML is turned over to ground operations.
Certifications will cover all the development work. “Certifications meaning where each and every subsystem will show their paperwork essentially,” Lanham explained.
“Showing where they tested, showing their data packages, and saying we’ve met our requirements and we’re ready to go. That gets bought off and then we’ll transition the system over to operations and they’ll begin operations and maintenance, so that kind of work will continue on the Mobile Launcher that’s got to occur periodically or however they have it laid out.”
“But the big phase will be finish testing and then get into the whole certification process,” he added.
The next trip to the launch pad for ML-1 is expected to be with the fully assembled Artemis 1 vehicle. Two trips to the pad are planned for the vehicle in this first launch campaign, the first for a Wet Dress Rehearsal (WDR), followed by a return to VAB for final inspections, stowage, and configurations.
CT-2 would then carry ML-1 and the Artemis 1 vehicle to the pad for a second time for a final week’s worth of launch preparations, including the two-day countdown to liftoff. Plans for the WDR and vehicle pad stays could change if NASA officially decides to skip the Core Stage Green Run test campaign at Stennis Space Center and substitute a short pad firing at KSC to speed up the launch schedule.
Lead image credit: Jack Beyer for NSF.