Mobile Launcher 1 (ML1, or ML) is on its way back to the Vehicle Assembly Building (VAB) at the Kennedy Space Center after successfully launching the SLS rocket and Orion/European Service Module duo on the Artemis I mission from Launch Complex 39B (LC-39B) on Nov. 16, 2022.
The ML now needs to be repaired from damage sustained during SLS’s debut launch as well as undergo a series of modifications to prepare it for its role on future SLS launches where crew will board the Orion for departure to the Moon and Lunar Gateway.
Post-Artemis I launch ML damage assessment
Overall, despite the amount of time it took to safely gain access to the ML due to elevator damage, the vast majority of the damage sustained from SLS’s first launch was as expected, according to David Sumner, Project Manager for ML1 on Artemis II, in an interview with NASASpaceflight.
“We had some expectations of some smaller equipment that we kind of expected we would see some damage, but we did see some other areas that some things happened that we weren’t fully expecting,” Sumner explained.
“The elevators took some damage. We have two elevators on the Mobile Launcher that go all the way up the tower. Those took some damage, and then we had some pneumatic and electrical panels, some that are up the tower, that took some damage as well that we were not expecting.”
Overall, Sumner explained that the ML structure itself was in good condition, and no modifications were needed to facilitate the ML’s rollback to the VAB.
“Immediately following launch, we had crews go out and start safing, doing the air checks and safing the ML,” added Sumner. “That took a couple of days, securing the ML, to allow other people doing structural assessments on the floor grating, making sure that the floor was safe to walk on.”
Toward mitigating the unexpected damage seen in post-flight analysis, Sumner said that metal banding straps would likely be placed around the panels and cabinets to ensure their doors remain shut, unlike their post-Artemis I condition.
Additionally, the elevators will require substantial refurbishment, and the blast doors which were in place for Artemis I to protect the elevator shafts and cars will also require upgrades based on their failures due to the power of the SLS rocket.
Conversely, the swing arms on the ML largely held up per preflight predictions, with some expected, minimal damage toward the ends of the arms noted.
Specifically, numerous soft goods materials on the swing arms, such as hoses and catch back nets, were lost during the launch.
However, it was an element of the ML that did not receive much attention during the Artemis I launch campaign — but that will be vital to Artemis II and beyond — that was the subject of critical post-liftoff checkouts.
This morning at 6:40 am EST, the mobile launcher atop the crawler transporter 2, had first motion in its roll back to the Vehicle Assembly Building following the launch of Artemis I on Nov. 16 at 1:47 am EST. pic.twitter.com/FETL4Embal
— NASA's Exploration Ground Systems (@NASAGroundSys) December 8, 2022
The Crew Access Arm (CAA) was exercised through its range of motion to ensure teams could maneuver it from its fully retracted position, which it needs to be in for center of mass considerations on the ML during rollback, to its fully extended position, which it needs to be in before entering the VAB.
“The other big constraint for us to roll back to the VAB was the Crew Access Arm,” said Sumner. “It was in a retracted position; in order for us to get into the VAB, we need to extend the CAA, and so at the pad, we were able to demonstrate that we could swing the CAA. That was a big deal.”
The only other item of note in terms of preparing the ML for rollback was removing and or securing any pieces of equipment that were loose.
In terms of lessons learned from the overall Artemis I pad flow and any modifications that might stem from that element of the process, Sumner noted that everything went fairly well in that regard.
Sumner did note, however, that there could be pending modifications to improve the liquid hydrogen systems on the ML due to issues faced during the various Wet Dress Rehearsal and counts; however, any modifications in that regard have yet to be finalized.
Refurbishment, modifications, and timelines for Artemis II
Unlike rollout and rollback operations with SLS, which were conducted without breaks, the rollback of the empty ML will take place across two days.
This break allows teams time to rest and not work overnight when not required.
The ML will be brought back to just outside the VAB on Thursday, Dec. 8, where it will then spend the night outdoors before teams resume roll operations on Friday, Dec. 9 to move the ML completely inside High Bay 3 of the VAB.
Once there, the ML will spend between four to six weeks undergoing continued post-launch assessments before the Crawler Transporter teams will pick up the ML and move it out of the VAB to the West Park Site — which is located to the north of the VAB and is the western-most of the two ML park sites.
“We’re pretty definite on January 2023,” said Sumner. “Sometime in January, we should be at the West Park Site.”
There, the ML will undergo a majority of its refurbishment and modification work, including installation of the critical Emergency Egress System hardware which will be needed for crew flight operations with Artemis II.
“What’s exciting for Artemis II is that’s going to be our first manned mission back to the Moon,” said Sumner. “And so the majority of our focus is really in the upper level of the tower of the Mobile Launcher, basically the 260-foot [79-meter] level and above.”
“And we’re really focused on that crew level, making sure it’s ready. Making sure the Crew Access Arm is ready for the crew, making sure that’s certified. Getting the Emergency Egress System installed, making sure it’s tested coming off the crew level.”
While at the West Park Site, the access platforms for the four egress baskets — which would be used to transport personnel safely away from the tower in the event of an emergency — will be installed.
“When we’re at the West Park Site, we’re planning to install three different platforms on the side of the ML tower, and one of those platforms is going to have a set of four hoists on top of it.”
The hoists are approximately 99 meters (325 feet) above ground level and will each have a cable that can stretch down to the ground.
This cable is critical to how the overall Emergency Egress System will be connected between ground architecture and the ML following rollout of a fully stacked SLS rocket destined to carry crew.
“When we get to the pad, we’ll stretch a cable down all the way to the ground surface and then out to the perimeter edge of Launch Complex 39B where our landing — we call it the terminus — area is. And we will tension those cables and connect them up to the tower.”
That will provide the zip-line-like wires — like those used throughout the Shuttle Program and still used at neighboring 39A for Falcon 9 crew launches — that the egress baskets would ride to the ground from the Crew Access Arm level of the ML.
Those hoists will be installed at the West Park Site, but their primary test and integration, as well as verification and validation, will have to take place at pad 39B.
Overall, the ML is expected to spend a few months at the West Park Site, though explicit timelines are not currently known due to the uncertainty that remains in post-Artemis I launch damage refurbishment timelines.
Also at the West Park Site, pneumatics changes will be carried out on the crew access level. Teams will also install breathing air and gaseous nitrogen stations and systems that would be needed in the event of emergencies.
Additional work at the West Park Site will also include modifications to the ignition overpressure protection/sound suppression system that were planned before the Artemis I launch.
“The ignition overpressure sound system down at the base of the ML where all the water comes out at time of launch — we’re making some modifications to the rain bird heads,” noted Sumner.
The change necessitates taking the heads off of the rain birds and installing new ones that will give the water a different flow across the ML as it deadens the acoustic environment at RS-25 engine and Solid Rocket Booster ignition.
Once these modifications and refurbishments are complete at the West Park Site, the Crawler Transporter will once again pick up the ML and haul it out to LC-39B for its Emergency Egress System testing.
After arriving at the pad and connecting the zip-line-like cables from the hoists to the landing area, the hoists will then be used to individually lift the four egress baskets to their proper positions, where the baskets will then be secured and locked in place ahead of testing.
At present, testing and validation of the Emergency Egress System will involve the use of weights and multiple runs of the baskets as well as drills to ensure personnel are familiar with how to utilize the system should they need to.
Prior to the commencement of the Shuttle program, the slide wire emergency egress baskets were never tested with humans, something that caused concern during STS-41D/Discovery’s on-pad abort in June 1984, which ended in an engine shutdown on the pad at T-6.4 seconds.
During that abort, launch personnel did not want to tell the crew to use the slide wire baskets as they had not been fully tested.
Following the Challenger disaster in 1986 and a need to re-certify the entire Shuttle program before STS-26/Discovery’s Return To Flight mission, emergency egress basket training with astronauts onboard was eventually performed; however, subsequent tests of the system utilized ballasts instead of humans.
According to Sumner, the current plan is to likewise use ballasts for testing and validation of the entire Emergency Egress System for SLS — though the eventual use of humans in a test has not been completely ruled out at this time.
This specific element of the ML’s return to pad 39B carries some uncertainty toward the overall schedule, as certifying the processes for installing the Emergency Egress System and validating its overall use could take “a little bit of time.”
Likewise, the Crew Access Arm will also be a focus of the ML’s return trip to 39B before stacking for Artemis II.
While the decision was made to install the arm and put it through some of its maneuvers during the Artemis I flow, it was notably not used at the same times when it would during a launch countdown with crew.
To that end, the CAA actually needs to be certified for human flight, and this will involve moving it during various wind events and at various wind angles as well as at different arm movement speeds.
All of this will validate and verify that the arm is safe for humans to be on during certain weather events as well as the arm’s ability to move under various wind profiles in the manner it will need to on launch day.
Under nominal operations, the arm will move very slowly away from the Orion capsule at T-6 minutes. But, should an emergency arise after that point that does not require activation of the Launch Abort System but might require the crew to quickly egress Orion and the ML, the arm would have to move back into position far quicker than when it retracted.
This is one of the movement tests that will be studied when the ML makes its return trip to the pad in 2023.
These specific tests for the CAA do not require a complete 100% capture of data at all the various wind levels and wind speeds the CAA might have to operate in.
For this particular part of CAA verification and validation, only 80% of the different variables are needed from a data standpoint, after which enough data will have been collected that models could simulate the remaining 20% and verify the entire envelope of wind load and directional operations the arm might encounter.
Once all testing and verification and validation operations are complete at LC-39B, the Crawler Transporter will once again pick up the ML and return it to High Bay 3 inside the VAB where final multi-element verification and validation work will take place.
Once these steps are complete, the Mobile Launcher will be ready for stacking operations for the Artemis II mission which will return humans to the vicinity of the Moon.
While the crew of Artemis II has not yet been announced, it is already known that a Canadian Space Agency astronaut will have one of the seats on board the mission — becoming the first non-American to travel to the Moon.
At present, Artemis II is planned to launch no earlier than mid-2024 on a free return trajectory which will involve a closest approach flyby to the Moon of 7,400 km.
(Lead image: The ML on its return trip to the VAB on Dec. 8 after successfully launching Artemis I on Nov. 16, 2022. Credit: NSF/Space Coast Live)