Artemis 1 SLS stacking work running long, preps for integrated tests continue in parallel

by Philip Sloss

Final securing of the Space Launch System (SLS) Launch Vehicle Stage Adapter (LVSA) to the Core Stage for Artemis 1 in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) in Florida was slowed down by issues discovered when workers started bolting the two elements together. NASA’s Exploration Ground Systems (EGS) and prime launch processing contractor Jacobs lifted the LVSA by crane up on top of the SLS Core on June 22 with mating expected to be finished that night; however, hard-mate was not completed for several days.

While the stacking procedures were delayed, other work in parallel tracks continued in different areas of the SLS vehicle. After the Core Stage was attached to its Solid Rocket Boosters in mid-June, post-Green Run repairs and refurbishment resumed along with preparations for upcoming vehicle power up and pre-launch testing and checkouts.

LVSA hard-mate issues

Hard-mate of the LVSA to the forward skirt of the Core Stage for Artemis 1 was completed on the weekend of June 26-27 after the SLS interstage connector was lifted into High Bay 3 earlier in the week. Lifting operations themselves for the LVSA were delayed by the quick onset of the new Juneteenth federal holiday; when the lift team returned after the three-day weekend, the 325-ton crane was attached to the adapter in VAB High Bay 4 during the day on June 21 to lift it off its transportation pallet for inspections and cleaning of the lower mating surface.

Overnight on June 21 into 22, the approximately 9 meter tall cone was lifted up above High Bay 4, across the transfer aisle into the High Bay 3 integration cell, and lowered onto the forward skirt of the Core Stage. The connection between the Core Stage and LVSA is a bolted flange, with 360 bolts fastening the two elements together at one-degree intervals around the circumference.

The flange was soft-mated on June 22, but according to sources, completion of hard-mate was delayed into the June 26-27 weekend — which pushed back the lift and mating operations for the Interim Cryogenic Propulsion Stage (ICPS) to no earlier than the middle of the week of June 28. The LVSA hard mate is a constraint to starting the procedures to lift the ICPS and mate it to the top of the stage adapter.

Credit: NASA/Frank Michaux.

(Photo Caption: The Launch Vehicle Stage Adapter is lowered down by crane early on the morning of June 22 into mating position in High Bay 3 of the VAB. The interstage adapter connects the two SLS stages together in the launch vehicle’s Block 1 configuration.)

It had been expected that hard mate would be completed by the end of the day on June 22, but work to fully secure the bolted connection was taking longer than anticipated. Ideally the mating surfaces would be perfectly flat, but there is some tolerance for the rings on the LVSA and the Core Stage not completely touching; however, sources noted gaps that were out of tolerance that needed to be addressed.

There was also an issue reported with the form and fit of splice plates, which are parts added to the flange to help fully mate them. A “tiger team” across the SLS program elements and contractors had been set up to address any issues that came up during stacking of the SLS flight hardware on the Core Stage, and the time consumed to resolve some of these “non-conformances” has been taken up as much by programmatic discussion and reviews as it has by hands-on work with the hardware.

Issues like these were expected in this first launch campaign. When assessing the schedule of work before the Core Stage arrived at KSC in late-April, EGS estimated as much as four months of risk to a six-month schedule of work.

The overall schedule impact of this issue could be different than with the delays getting the Core Stage mated to the SLS boosters because all the integration work was held up behind that critical milestone. Stacking the upper SLS elements on top of the Core Stage is a constraint to some upcoming work, but not all of it; it remains to be seen how much of the slip will translate to the bigger milestones downstream.

However, once all the bolts are completely torqued and hard-mate of the LVSA is completed, work will start to cover the flange and metal substrate around it with spray-on foam insulation; that work will continue over several days while the rest of the SLS and Orion test hardware is stacked above.

In addition to being the structural interstage connector, the LVSA also houses most of the ICPS, including its single RL-10B-2 engine and stowed nozzle extension during launch and ascent. Circular doors around the circumference of the adapter allow access inside to perform pre-launch servicing of ICPS hardware.

During ascent to orbit the LVSA stays bolted to the Core following Main Engine Cut-Off (MECO), with the ICPS separating from the top of the LVSA. A separation system and a frangible joint assembly is sandwiched by the ICPS and LVSA.

The frangible joint assembly instantaneously separates the in-space ICPS stage from the LVSA at the appropriate time without generating any debris from the explosive detonation. The outside of the LVSA is covered with spray-on foam insulation, which thermally protects the adapter and its contents from heating during ascent through the lower atmosphere.

Credit: NASA/Frank Michaux.

(Photo Caption: The ICPS for Artemis 1 waits in the VAB Transfer Aisle on the afternoon of June 21 as the LVSA waits in High Bay 4 in the background hanging on one of the heavy cranes in the VAB. Following the new Juneteenth holiday weekend, final lift preparations were completed on June 21 and lifting operations began during the overnight shift.)

The adapter also includes electrical harnesses to connect the Core Stage flight control system with the LVSA separation system, ICPS flight computers, and the Orion spacecraft and crew above. The adapter is also covered with development flight instrumentation (DFI) for its first launch, and all of those sensors are connected to the Core Stage’s data acquisition system.

The two cameras in the stage adapter are among several mounted around the launch vehicle, that are wired into the Camera Control Unit (CCU) in the Core Stage’s intertank, that will collect data during launch and ascent. Views from the LVSA cameras capturing ICPS separation will be relayed via telemetry to ground receiving stations.

Next steps leading to SLS power up, first ITCO tests

The EGS/Jacobs integrated operations team is working different tasks in parallel towards the goal of performing the first tests in the Integrated Test and Checkout (ITCO) campaign. Following mating of the Core Stage to the SLS boosters in mid-June, teams split up to work in different areas of the vehicle and ground-based launch support hardware.

Post-Green Run “traveled work” has resumed on the Core Stage engine compartment now that it is vertical again, and Mobile Launcher umbilicals are being connected to the stage. Installation of new sections of cork on the base heatshield has started; areas of cork that were charred during the 8 minute Hot-Fire test in March were removed in May while the Core Stage was horizontal in the VAB Transfer Aisle.

For stacking, once all the LVSA constraints are cleared, the ICPS is the next element in the stacking sequence.

Following the ICPS, two more test articles remain to be placed on top of the vehicle in support of the first round of testing, the structural test article (STA) for the Orion Stage Adapter (OSA) and a Mass Simulator for Orion (MSO). The test hardware will be used to support powering up the integrated SLS vehicle for the first time as well as the first three major ITCO tests.

The connections between all of the SLS flight hardware and the Mobile Launcher will be checked out in an Interface Verification Test (IVT), followed by an Umbilical Release and Retract Test (URRT). The URRT will test the Mobile Launcher’s launch release system, which must safely detach the ground umbilical connections from the vehicle beginning at T0 and quickly swing the umbilical arms away.

Credit: NASA/Cory S. Huston & Chris Swanson.

(Photo Caption: All the flight and test hardware that will be used during the early part of Integrated Testing and Checkout (ITCO) can be seen in this image taken from High Bay 4 on June 21. The mostly-obscured SLS Core Stage and Boosters can be seen in the background across the aisle in High Bay 3.  In the foreground in High Bay 4 from left to right are the Orion mass simulator, the structural test article (STA) of the Orion Stage Adapter, and the LVSA.  The ICPS parked in the Transfer Aisle can also be seen just to the right of the LVSA.)

After the URRT, an Integrated Modal Test (IMT) will collect data on the structural dynamics of the SLS and Orion simulator.

The OSA STA is standing in for the flight adapter for the first ITCO tests to provide more schedule flexibility for installing the set of 13 Cubesats that will fly inside the OSA during Artemis 1. The MSO is low-fidelity test hardware that has roughly the same mass and center of gravity as the Orion launch stack. Adding those two test articles on top of ICPS is now forecast to begin no earlier than the week of July 6.

However, some of the Core Stage refurbishment and other traveled work from the Green Run campaign must be completed before those tests can begin.

Access doors to the engine section on the Core Stage have been re-opened and a two-level platform kit is being reinstalled to provide internal access to all of the equipment in the aft compartment. This will allow some of the transportation deconfiguration work that needs to be done in conjunction with powering up the SLS vehicle systems in the Core Stage and boosters.

It has also been decided to remove and replace the clutch mechanisms on the Core Stage Main Propulsion System (MPS) prevalves. The mechanisms in two of the prevalves failed during pre-test checkouts at different times in the Green Run campaign.

Although the prevalves operated to specification during the Green Run test cases, the failures were unexpected and delayed the final critical tests by several weeks.

The current plan is to remove and replace most of the prevalve clutch mechanisms before the URRT. All the internal work platforms will have to be broken down and removed before that test; after the umbilicals are later reconnected and internal access re-established, the rest of the clutch mechanisms will be repaired.

Credit: NASA/Cory Huston.

(Photo Caption: The aft end of the Artemis 1 Core Stage hasn’t quite reached its resting place during lifting operations on June 12. While the different programs work through issues with stacking, other workers are busy inside and outside the engine compartment of the Core. New sections of cork are being installed on the base heatshield outside and inside work platforms are being installed to reconfigure the Main Propulsion System from transportation to supporting the upcoming pre-launch checkouts.)

In addition to stacking the rest of the flight and test hardware, the Mobile Launcher umbilicals, swing arms, and other connections to the vehicle need to be connected before the first power up and initial ITCO tests can begin. Once the umbilicals are connected, the SLS systems on the Core Stage and boosters will be powered up for the first time together. Although the avionics and software for the Core Stage and boosters have completed integrated certification testing, this will be the first time they are activated in a non-emulated environment.

Part of the plan to prepare SLS for its integrated series of tests involves powering up the vehicle to reconfigure some of the Core Stage systems from their transportation configuration. Before the stage was lifted out of the B-2 Test Stand at the Stennis Space Center, parts of the MPS, including valves, were configured for water transportation to KSC. In order to reposition those valves now that the stage is at KSC, the SLS flight computers in the Core Stage need to be powered up.

A more thorough checkout of the electrical connections will then be made in the Interface Verification Test (IVT); the first major test in ITCO, the IVT will validate that all the SLS flight systems and EGS 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 during the first test.

The URRT follows after the IVT; it 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.

With the umbilical plates disconnected and the all the umbilical arms swung away after the URRT, the SLS and Orion mass simulator along with the Mobile Launcher will be in the proper configuration for the Integrated Modal Test, which is the final test in the sequence of three. The flight and test hardware will only be attached at the booster aft skirts to eight Vehicle Support Posts on the Mobile Launcher.

Credit: NASA/Glenn Benson.

(Photo Caption: As seen from the upper management level of Firing Room 1, the Artemis 1 launch team practices countdown and troubleshooting procedures during a terminal countdown simulation on June 24. The Integration Console area in the middle background manages troubleshooting and resolve issues that come up during the simulation exercises and the test directors and test conductors in the foreground oversee completion of the overall countdown.)

Also running in parallel to the stacking, umbilical connections, and traveled work, preparations for the Integrated Modal Test are also continuing. Hundreds of sensors are being installed all over the vehicle and wiring is being run to and from the sensors collect data for the test.

Elsewhere, the launch team gathered on console in Firing Rooms 1 and 2 of the Launch Control Center adjacent to the VAB on June 24 for a terminal countdown simulation. The training exercise was the last standalone simulation performed in a series of rehearsals leading up to the Artemis 1 launch.

Going forward, the launch simulations will be integrated with mission control and engineering support teams at other NASA centers. The integrated simulations will help the different teams practice troubleshooting together while working on failure scenarios thrown at them.

Simulation teams script out failure scenarios to throw at the launch team and support rooms during the exercises. The training helps the team work out the choreography for troubleshooting and the timing of decision making for the types of multiple, simultaneous problems they may have to face during real launch attempts with time constraints imposed by lunar launch windows.

Lead image credit: NASA/Kim Shiflett.

Related Articles