After a month of thermal protection system foam repairs and other preparations, workers with NASA’s Exploration Ground Systems (EGS) and prime test operations and support contractor Jacobs at the Kennedy Space Center in Florida started lift operations on the Space Launch System (SLS) Core Stage for Artemis 1 in the Vehicle Assembly Building (VAB) on June 10. Early on June 11, two of the overhead cranes in the VAB rotated the Core Stage from horizontal to vertical in the Transfer Aisle.
Work will continue over the weekend of June 12-13 to lift the stage up into High Bay 3, position it in between the two SLS Boosters already stacked on Mobile Launcher-1, and bolt them together.
Lift and breakover begins after extended TPS repairs
The first flight SLS Core Stage was finally rotated to its vertical launch orientation at KSC early on the morning of June 11. It was expected to be lifted from the transfer aisle up towards the ceiling of the VAB and then over into High Bay 3 to be lowered into place between the two SLS Solid Rocket Boosters (SRB) stacked on the Mobile Launcher.
“Stacking” of the Core and Boosters is be a big milestone in any SLS launch campaign, but work on all the other Artemis 1 flight hardware at KSC was delayed waiting for this Core Stage lift and eventual mate, increasing its significance in even this first launch processing flow. Once the mate is completed, the Core-Boosters “partial stack” will allow the EGS and Jacobs integrated operations team to branch out on parallel work activities to fully stack the rest of the vehicle, conduct special first-time tests, and finish pre-launch checkouts.
The SLS Core Stage was the final element to arrive for launch, completing its special Green Run design verification campaign in April and arriving at KSC later that same month.
Following the full duration test-firing of the stage in the B-2 Test Stand at Stennis on March 18, some post Green Run refurbishment work was deferred until after the Core was shipped to Florida. Standard post-firing refurbishment of the four RS-25 Core Stage engines was completed at Stennis, but work to refurbish the stage’s foam insulation for its cryogenic propellant tanks and the foil and cork heat protection around the base heatshield were deferred to KSC.
After four weeks of thermal protection system (TPS) refurbishment work and standard post-arrival preparations, scaffolding around the stage was removed, purges were disconnected, and self-propelled motorized transporters (SPMTs) were used to move the carriers with the Core Stage on board north in the transfer aisle, on June 6, to the area in between the VAB’s high bays to prepare for dual-crane operations to reorient the Core from horizontal to vertical and then lift it into High Bay 3 for mating to the Boosters.
A “lift spider” was again attached to the front of the Core Stage the next day on June 7; the approximately 20-ton, yellow lifting fixture is identical to another unit that stayed attached to the stage at Stennis for the whole Green Run campaign. The fixture provides the forward lifting point for the stage.
Once the stage was moved into the north transfer aisle, it had been expected that the team would press into lift operations; however, completing all TPS repair work delayed the final lift. Delays were anticipated during this first-time-through launch vehicle and spacecraft integration process for Artemis 1, and EGS planned for the work to take a risk-assessed 10 months to complete once the Core Stage arrived at KSC.
EGS assessed as much as four months of risk to a schedule showing six months of work; the current no earlier than (NET) date for launch readiness is late-November, but going through the first-time learning curves and accumulating delays of a few days here and there is more likely to push launch readiness into early 2022. The fully “risk assessed” launch readiness date is March 2022.
After the additional TPS work was completed in the north transfer aisle, lift preparations resumed on June 9 with the connection of the two cranes to raise the Core Stage off its transportation carrier. One of the two 325-ton VAB cranes was attached to the lift spider, and the 175-ton transfer aisle crane was hooked up to lift points on the structural ring of the stage’s engine section.
After the lift started on June 10, with the cranes taking up the load of the Core Stage from its carrier pieces, workers performed a breakover operation early on the morning of June 11 to rotate the stage vertical where it could be controlled by the single 325-ton crane on top. The trailing lifting fixture and crane were disconnected.
The next major step will be to lift the stage up into the diaphragm opening between the transfer aisle and the High Bay 3 integration cell.
The crane will then lower the stage down into position between the two Solid Rocket Boosters. To create extra clearance while the Core is being lowered between them, “puller straps” will be used to pull the boosters slightly outward.
The stage has both forward and aft attach points where it will be bolted to the SRBs. A thrust beam runs through the middle of the intertank in the Core, between the forward attach points of each booster, to help channel the loads of the SRB thrust during launch.
In the forward “ball and socket” connection, the Core Stage and the sockets on its fittings rest on top of the Booster attach points — where a separation bolt will join them. Three struts on the aft end of each Booster connect to the engine section of the stage.
Pre-mate Core Stage work
Moving the Core Stage into position was only possible after completing post Green Run TPS refurbishment work in the VAB Transfer Aisle where it could be done with less weather interruptions versus outside in the B-2 Test Stand. The VAB also provides better access to the stage in a horizontal orientation.
The stage was rolled off NASA’s Pegasus barge on April 29 and taken into the southern part of the VAB transfer aisle. After the stage and its transportation carrier were set down in the low-bay area of the transfer aisle, scaffolding was set up for repairs to the acreage and for closeout foam sprays where cracks had developed during propellant loading cycles and the long test-firing at Stennis.
After EGS and Jacobs completed receiving inspections of the stage, an approximately four-week timeline was established to perform all the foam repairs and refurbishment — mostly at the forward end of the vehicle. Within that same timeline, more typical Core Stage KSC arrival activities like installation of Flight Termination System (FTS) components were completed as well. Given the opportunity of time, it was decided to also start the cork TPS work on the bottom of the stage by removing the burned areas on the base heatshield.
“We had time and resources available to work it ahead of stacking,” Michael Alldredge, NASA SLS TPS Subsystem Manager, said in an email. He added: “We didn’t really know how difficult it would be to get [the damaged cork] off, so we wanted to start as soon as possible in case we ran into problems.”
The engine section and the boattail at its aft end are covered with cork panels, which are then coated with a white paint that acts as a moisture barrier. For the Green Run test-firings, the boattail was covered with an additional layer of foil tape to protect against the extra heat generated during a full eight minute flight-duration firing of the four-engine RS-25 cluster.
The aft face of the boattail, the base heatshield, took the brunt of the heating during the test-firing; adjacent areas such as the boattail fairing and the engine section barrel suffered little heat damage.
For the repair, Boeing removed some of the affected cork and also started removing leftover foil tape. The base heatshield refurbishment will now be completed after stacking, where work can be done without much conflict with the integrated test and checkout of the vehicle.
“There is a good bit of TPS work to perform on the base heat shield once we get into the High Bay,” Alldredge said. “We took the damaged cork off in the transfer aisle, and will re-install and paint it in the high bay.”
Preparations for Integrated Test and Check-Out next
Once the Core is fully mated to the boosters, work in the High Bay will branch out in parallel on multiple paths to get ready for power up and Integrated Test and Checkout (ITCO) operations of the Artemis 1 vehicle. Assembling the rest of the SLS elements on top of the Core Stage will occur in parallel with connecting the Mobile Launcher umbilicals to the Core and preparing for an Integrated Modal Test.
Stacking of the upper SLS elements will begin with the Launch Vehicle Stage Adapter (LVSA), which will be lifted on top of the Core Stage and bolted into place. That operation is currently scheduled for the week of June 14 but is dependent on completion of Core Stage mate operations.
The Interim Cryogenic Propulsion Stage (ICPS), derived by United Launch Alliance from its Delta IV launch vehicle, would be stacked next. The ICPS is currently in the Multi-Payload Processing Facility (MPPF), where it was loaded with hydrazine for its attitude control system on June 4.
It is currently scheduled to be moved to the VAB the week of June 21.
Because this is the first time an SLS vehicle is being integrated, 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 perform the stacking work.
After the ICPS is stacked, an Orion Stage Adapter would follow, with the first round of stacking being completed with a Mass Simulator for Orion, after which teams will perform an Interface Verification Test that will see the EGS ground control system power up the fully assembled SLS for the first time.
The Interface Verification Test will validate that the vehicle and ground systems are correctly connected and operating with each other.
After this, an Umbilical Release and Retract Test will occur to ensure all of the Mobile Launcher’s swing arms can properly and safely detach and swing away as planned from the vehicle.
The Integrated Modal Test, where workers shake the vehicle, will follow at the end of the first series of tests.
While the initial SLS powered checkout and modal testing is being performed in the VAB, the Artemis 1 Orion spacecraft will complete its standalone, “offline” processing. Like the ICPS, Orion is currently in the MPPF, now with its flight commodities fully loaded. After completing propellant loading of the Service Module in April, the Crew Module’s gaseous helium tanks were loaded in early-May ahead of Crew Module hydrazine tank fueling in mid-May.
Current plans are for Orion to be moved to the Launch Abort System Facility for its final offline outfitting for launch, where the inert Launch Abort System (LAS) for Artemis 1 — which combines a live jettison motor with inert abort and attitude control motors — will be stacked on top of the Crew Module. Four ogive-shaped fairing panels will also be installed to encapsulate the Crew Module.
After the LAS is installed and the first round of SLS testing is completed in the VAB, Orion will then be transported to the VAB to be lifted and mated to SLS no earlier than mid-August.
The Artemis 1 mission management team is currently working through flight readiness analysis cycles, calculating lunar launch opportunities and vehicle performance margins. Currently, the first launch period available for an NET late-November 2021 readiness date is Launch Period 15, which opens on November 23 and runs through December 10. Following that, Launch Period 16 is December 21 through January 3, 2022, with Launch Period 17 running January 17 through January 30.
(Lead image credits: NASA/Cory Huston.)
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