The integrated operations team of NASA’s Exploration Ground Systems (EGS) and prime launch processing contractor Jacobs completed mating the SLS Core Stage for Artemis 1 with its boosters on June 13, another in a series of firsts that will culminate in the debut flight of NASA’s new launch vehicle, currently projected for no earlier than late-2021. After the stage was raised off its transportation carrier and rotated vertical, the backbone of the launch vehicle was lifted up into High Bay 3 of the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) and bolted to its two Solid Rocket Boosters (SRB).
The physical combination of the large SLS elements was a big step in the overall Artemis 1 launch campaign. Now that the Core Stage and boosters are bolted together, EGS and Jacobs can now branch work out into parallel paths, beginning to plug SLS into the EGS control system to prepare for months of testing and checkouts while continuing to stack the rest of the launch vehicle and eventually the Orion spacecraft.
Parallel work paths on mated “partial stack”
The first flight SLS Core Stage and boosters were “soft-mated” around 9 pm Eastern on June 12 and “hard-mated” at approximately 6 am on June 13, after six weeks at KSC of post-Green Run refurbishment, lift preparations, and then crane operations in the VAB to move the Core into place with the boosters on the Mobile Launcher. Two cranes lifted the stage off of its transportation carrier on June 10 and rotated it from horizontal to vertical during the midnight hours on the night of June 10 into June 11. With the heavier 325-ton crane at the top, the 175-ton trailing crane was disconnected from the bottom to allow the stage to be lifted into High Bay 3 for mating.
That lift “up and over” the spacing between the VAB Transfer Aisle and High Bay 3 was conducted the next night, from June 11 into June 12. The crane then lowered the stage down and between the two SLS boosters and into position to be mated.
When connected, the Core’s primary forward attach points rest on top of the boosters’ forward attach interfaces. The forward Core Stage attach fittings are at the ends of the main thrust beam running through the intertank. Once fully mated, the weight of the Core Stage is supported by the boosters.
At liftoff, the boosters will pick up the Core Stage through the intertank thrust beam and hoist the whole flight vehicle into the sky. After the boosters burn out, separation bolts will disconnect them from the Core Stage — with booster separation motors firing to push them safely away.
(Photo Caption: Core Stage-1 is lowered in between its two SLS Boosters (left) and suspended on one of the VAB’s heavy cranes while the flight hardware was bolted together (right) on June 12. Lift operations started on June 10 and mating operations extended through the weekend of June 12-13.)
Mating of the “partial stack” of the Core and boosters is a major milestone in the first Orion/SLS launch campaign. The SLS Core Stage was the final Artemis 1 flight hardware element to arrive for launch in late-April, completing its double-duty as the program’s propulsion test article for the special Green Run design verification campaign.
The structural connection also marks the beginning of the next phase of integration and testing, which gets more complicated. The hard-mating of the Core Stage and boosters also allows a branching out of multiple work paths over the next several weeks.
“I think for us it really comes down to what are the critical path priorities,” Andrew Shroble, Integrated Operations Flow Manager for Jacobs, said in a late-April interview. “There’s a lot of parallel work that’s going to be happening once we stack and get the Core Stage mated to the boosters.”
Artemis 1 is the first flight for the EGS launch processing infrastructure and for almost all of the Orion and SLS flight hardware elements; so the road to the launch pad still has some special first-time, pre-launch tests as part of an overall Integrated Test and Checkout (ITCO). After the SLS is assembled and fully connected to the Mobile Launcher and ground processing system, three major tests will be performed with an Orion mass simulator stacked on top.
A fully-integrated SLS will be powered up for the first time for an Interface Verification Test (IVT), followed by an Umbilical Release and Retract Test (URRT); the final test in the sequence is an Integrated Modal Test (IMT).
The Interface Verification Test will validate that the SLS flight and ground systems are correctly connected and operating with each other. The physical interfaces between the ground-side and flight-side umbilical plates will also be leak-checked.
After the IVT, the Umbilical Release and Retract Test will time the Mobile Launcher’s launch release system, which must safely detach the ground from the vehicle beginning at liftoff and quickly swing the umbilical arms away.
(Photo Caption: NASA diagrams of the forward and aft connections between the SLS Core Stage and Boosters. The left diagram is a side cross-section of the attachment that shows that the Core Stage (CS) rests on top of the Boosters (SRB). The right diagram is looking down the length of the vehicle from the top towards the bottom to show the three struts that connect each booster to the engine section on opposite sides of the Core.)
With the umbilical plates disconnected and the arms swung away after the URRT, the SLS and Orion mass simulator along with the Mobile Launcher will be configured for the Integrated Modal Test. The flight hardware and simulator will only be attached at the booster aft skirts to eight Vehicle Support Posts on the Mobile Launcher. Input devices like mechanical shakers will be used to ring the structure to collect data on the structural dynamics.
The IMT will mark a checkpoint in the middle of the Artemis 1 launch campaign; once completed, the Orion spacecraft simulators will be destacked and the Artemis 1 Orion spacecraft will be brought in for stacking while the launch umbilicals are extended to reconnect the full first-flight vehicle to the ground control system.
The parallel-track processing is working towards the three tests simultaneously. “There’s a huge goal to get the whole vehicle stacked; there’s another huge goal to get connectivity and be able to power up as soon as you can to troubleshoot and get through any challenges we’ll have there. And then you have a lot of work that has to happen to get ready for the tests down the line, like the Integrated Modal Test,” Shroble said.
“If we run into an obstacle or we have a non-conformance issue, then we move on to the next priority so you’re keeping all these critical paths moving forward at all times. If you run into a kink, you move on to the next.”
In parallel with preparation for the Integrated Modal Test later in the processing flow, the rest of the SLS is now preparing to be stacked on top of the Core Stage. The upper SLS elements can now line up for their turn, beginning with the Launch Vehicle Stage Adapter (LVSA). The LVSA is staged in High Bay 4 of the VAB, and current plans are to begin operations to lift and mate it to the top of the Core Stage as early as Thursday, June 17.
The Interim Cryogenic Propulsion Stage (ICPS) and an Orion Stage Adapter (OSA) article would follow before a Mass Simulator for Orion (MSO) completes the assembly for the first part of Integrated Test and Checkout.
The lower flange on the LVSA will be bolted to the forward skirt of the Core Stage and then that mated flange will be closed out with spray-on foam insulation. The MSO doesn’t represent the form and fit of Orion, but it does mimic the mass and center of gravity of the spacecraft in its launch configuration and can stand in for the spacecraft for the Integrated Modal Test, which is planned as a one-time only exercise.
(Photo Caption: The Artemis 1 Core Stage is seen after being lifted up near the top of the VAB on June 12. It was rotated from horizontal to vertical in the transfer aisle that runs from top to bottom in this view. After reaching this point, the 325-ton crane translated the stage through the opening into High Bay 3 on the right.)
“At that point we’ll have the stack that we’re going to use for modal,” Cliff Lanham, NASA Senior Vehicle Operations manager for EGS at KSC, said in a March interview.
The ICPS itself is ready to be stacked; it is currently in the Multi-Payload Processing Facility (MPPF) where loading of its attitude control system tanks with hydrazine was completed on June 4. The in-space stage for SLS Block 1 could be moved from the MPPF to the VAB late this week or early in the week of June 21.
Because this is the first-time a full SLS vehicle is being integrated together, the SLS Program and its contractors have formed a quick response “tiger team” to be ready for any issues that come up as EGS and Jacobs run through checklists of the stacking procedures. Engineers, management, and technical leads from the SLS Program and its elements, SLS Boosters prime contractor Northrop Grumman, Boeing, LVSA prime contractor Teledyne Brown Engineering, and ICPS prime contractor United Launch Alliance (ULA) will support the structural and functional connections between the SLS first-flight hardware.
As more of the flight vehicle is assembled, additional preparations for the modal test can be completed. “We’ve got to install the rest of the [modal test] sensors on the upper elements; we’ve got to run the cables and do all the cabling routing and connectivity to be in a configuration to go do that test,” Shroble noted.
Preps for first vehicle power-up and interface testing
Immediately after the Core Stage and boosters were hard-mated, the forward skirt area became a busy location with preparations for stacking the LVSA as well as getting the Core Stage Forward Skirt Umbilical connected. The first task was to open up access to the forward skirt volume by using the still-attached crane to remove the lift spider and weather cover, the latter of which has been attached to the Core Stage since New Year’s 2020.
“Once we’re hard-mated to the boosters, they have direct access to that [forward skirt] flange, so they’ll disconnect the weather cover and the lift ring, and the weather cover will fly with the [lift spider on the crane]. And that’ll be de-integrated in the transfer aisle offline,” Shroble said.
The forward skirt umbilical mates close to the LVSA forward skirt flange region, so that connection will have to wait for foam sprays in the arc where the umbilical connects. “The Core Stage Forward Skirt Umbilical [connection] we have to balance that out around the LVSA foaming operation to make sure we get that portion of the flange done [and] also balance that out with the RINU optics.”
(Photo Caption: As seen from high on the umbilical tower of Mobile Launcher-1, the Core Stage is suspended in position in High Bay 3 to be connected to the two SLS Boosters on June 12. Over the next few weeks, the rest of the SLS flight hardware will be stacked on top, along with an Orion mass simulator for upcoming testing and checkout of the launch vehicle and ground control systems.)
The next step will be a redundant inertial navigation unit (RINU) optics survey that must be completed before LVSA stacking can begin. The RINU is installed at the apex of the forward dome of the liquid oxygen tank. “The survey itself is done on the mounting plate that is on the dome,” Shroble said.
“They actually do install a portion of the access kit so they can get to the RINU and be able to put hands on it. The optics is going to be a quiet bay, so obviously any work is going to have to stand down. So we do a lot of pre-coordination and pre-planning to make sure that happens on an off-shift or in a time-frame that would limit the impacts.”
“We’re looking to get the optics done to free up the ability to then go stack the LVSA as quickly as possible,” he added.
Down below, preparations to connect the umbilicals also picked up in parallel right after the Core and boosters were hard-mated. “The Tail Service Mast Umbilicals will actually require internal access to the engine section to be able to vent the lines down before we actually mate the umbilicals, so [establishing access to the engine section] is one of the first things that we do,” Shroble added.
The engine section was closed out for transportation in the test stand at Stennis back in April; after gaining access, there will still be a significant amount of work before the umbilicals are mated, including installing work platforms. For the Core Stage Intertank Umbilical, Shroble noted: “we’re able to swing that out and mate that as soon as possible. It doesn’t require internal access, so that’ll be something we look to do right out of the gate.”
Another piece to the power-up puzzle is the set of ground-side umbilical plates for the Core Stage. The plates connect and seal to the vehicle’s flight-side plates and were used at Stennis throughout powered testing of the vehicle there. In contrast to the launch configuration where the plates are quick disconnects, at Stennis they stayed connected through the major test activities including the test-firings.
Following the Green Run, the ground-side plates were disconnected and sent back to the Michoud Assembly Facility in New Orleans for refurbishment before being shipped to KSC to support the launch campaign, where they were connected to the umbilical arms and the vehicle.
(Photo Caption: A composite view of the Core Stage while hanging from one of the VAB’s 325-ton cranes on June 11. Running nearly its entire length, the stage’s systems tunnel is a prominent feature on its -Y side. The tunnel houses power and data lines to interconnect computer systems positioned throughout the stage; the lighter colored cover plates were added at KSC in May.)
Another connection from the Mobile Launcher to the forward skirt is the Vehicle Stabilizer System (VSS), which is a liftoff-released, two-point attachment that helps dampen vehicle motion on the Mobile Launcher due to winds when it is outside, either on the launch pad or while it is being moved between the pad and the VAB. The VSS is a structural connection, so there’s less urgency to get it connected while all the integrated testing goes on indoors in the VAB.
“[The] Vehicle Stabilizer is a good example of looking at constraints [to] help you determine what the priorities are,” Shroble explained. “The Vehicle Stabilizer will need to be mated before the Integrated Modal Test, but we know we need the Core Stage Forward Skirt [Umbilical mated] to be able to power up the vehicle. We know we need to get that Launch Vehicle Stage Adapter and Core Stage forward flange closed out and foamed. So the Vehicle Stabilizer isn’t as much of an urgent mate as the other umbilicals would be.”
“Any work we can get into and done and behind us: that’s the whole goal. But you’re looking to get as much work done as you can without impacting critical path,” he added. “It’s kind of a fine balance, and it’s a very busy time.”
For the first round of tests through the Integrated Modal Test, the structural test article (STA) of the Orion Stage Adapter will be stacked with the rest of the SLS vehicle and the Orion mass simulator rather than the flight article. The STA was brought to Kennedy in 2020 as a backup option; using it for the modal test provides additional time to receive all 13 secondary Cubesat payloads and install them into a deployment mechanism inside the flight OSA.
A few of the smaller Cubesat teams faced larger impacts from technical and pandemic issues over the last year. “Some of them have had challenges, both technical challenges with some of their propulsion or (communication) issues, but they’ve also had COVID-related challenges,” Marcos Pena, NASA Spacecraft Element Operations manager for EGS at KSC, explained in March. “These cubesats are for the most part developed by small teams on shoestring budgets, so technical impacts and personnel impacts hit them pretty hard.”
After all the Integrated Modal work is completed, the MSO will be removed first, followed by disconnecting the OSA STA. While umbilicals are reconnected to the vehicle, the flight OSA with all its cubesats installed will be brought into the VAB and mated on top of the ICPS and then Orion would follow shortly afterwards.
Lead image credit: NASA/Cory Huston.