WASHINGTON — NASA has stopped work on a second mobile launch platform intended for an upgraded version of the Space Launch System the agency no longer plans to develop.
At a March 29 briefing, Shawn Quinn, manager of NASA’s Exploration Ground Systems program, said the agency had issued a stop-work order for Mobile Launcher 2, or ML-2, the launch platform that NASA was building for the SLS Block 1B rocket.
He said NASA will take hardware from ML-2 and use it as spares for the existing mobile launch platform that supports the Block 1 version of SLS used on Artemis 1 and 2 launches.
“We pivoted the team to begin removing some of the hardware that is common on Mobile Launcher 1 that we can use as critical spares,” including items that have long lead times to build. “We can put them to good use in future Artemis missions supporting Mobile Launcher 1.”
In a March 30 interview, Quinn discussed some hardware from ML-2 they want to preserve as spares. “The umbilical arms for the core stage and the Orion, they’re identical” between the two platforms, he said. “The umbilical arms have parts on them that take a very long time to make, such as cryogenic flex lines.”
“We’re going to take the arms off and we’re going to put them into storage and properly care for them so they can be used if we need to have parts for Mobile Launcher 1,” he said.
ML-2 was designed for the Block 1B version of SLS, which would have used the larger Exploration Upper Stage. That required a different platform than the existing one for the SLS Block 1 and its smaller Interim Cryogenic Propulsion Stage (ICPS), including umbilical arms at different locations on the launch tower.
However, NASA announced Feb. 27 it would no longer pursue the SLS Block 1B, seeking to standardize on a “near Block 1” version to enable an increased flight rate for upcoming missions. NASA later said it would replace the ICPS, of which there is only one remaining, with a version of the Centaur upper stage for future SLS missions.
Development of ML-2 suffered serious cost overruns and schedule delays. NASA awarded Bechtel a $383 million cost-plus contract in 2019 to build ML-2, then scheduled for completion in March 2023. However, a 2024 report by NASA’s Office of Inspector General concluded that ML-2 could cost NASA up to $2.5 billion, with the risk that the platform might not be ready until 2029.
“Because Bechtel underbid on a cost-plus contract in order to, what appears, to get it,” then-NASA Administrator Bill Nelson said at a May 2022 Senate hearing, “they couldn’t perform. And NASA is stuck.”
Bechtel did not respond to a March 30 request for comment on NASA’s stop-work order.
With the successful launch of Artemis 2 on April 1, NASA is now beginning to review how the mobile launch platform handled the liftoff of the SLS. That platform suffered more damage than expected during the Artemis 1 launch in 2022.
“We had a fair amount of repairs to do to tubing, to the elevators and to other equipment on the mobile launcher,” Quinn said in an interview. “We learned from Artemis 1 and we redid our models for the kind of plume damage that we might get as the rocket leaves the mobile launcher.”
NASA worked to harden the platform, he said, putting stronger blast doors in place to protect the elevators. Workers also improved a system designed to spray down the platform with water to wash away residue from the solid rocket booster exhaust. A broken gaseous nitrogen line prevented that system from working as planned on Artemis 1, requiring the replacement of hundreds of meters of tubing that was corroded by the residue.
Initial reviews suggest the mobile launch platform held up better on Artemis 2. “Our initial assessment is showing that most of the damage is largely cosmetic,” said Lori Glaze, NASA acting associate administrator for exploration systems development, at an April 2 briefing. “Overall, everything is looking pretty good, especially when compared to Artemis 1.”