Umbilical hardware arrives for SLS ML-2, runs out of funding

by Chris Bergin

The construction of NASA’s second Space Launch System Mobile Launcher (ML-2) has been delayed after NASA ran out of near-term funding. ML-2 is required due to the increase in height for the Block 1B version of the rocket, making it incompatible with the billion-dollar ML-1. However, some planned work will continue, such as testing umbilicals that have arrived at KSC at the Launch Equipment Test Facility (LETF).

SLS already has a Mobile Launcher (ML-1), converted from its role with the defunct Ares-I rocket. It now hosts the Artemis 1 SLS – stacked on the ML – inside the Vehicle Assembly Building (VAB) ahead of rollout to Pad 39B.

The plan has always been to swap Block 1’s Interim Cryogenic Propulsion Stage (ICPS) with the more-capable Exploration Upper Stage (EUS), in turn moving to the SLS Block 1B variant for the Artemis 4 mission.

The ICPS is a renamed and modified five-meter Delta Cryogenic Second Stage currently used on Delta IV Heavy rockets and was previously used on the Delta IV M+ five-meter upper stage configurations of the Delta IV family. The EUS sports four RL-10 engines.

The challenge faced by NASA’s Exploration Ground Systems (EGS) Program revolved around catering for the Block 1B rocket, which is slightly taller than Block 1 and thus incompatible with ML-1.

Side-by-side comparison from 2016 of the Block 1 vehicle and ML umbilical tower configuration (left) and the Block 1B configuration. Prior to funding ML-2, the single Mobile Launcher was going to be partially taken apart and rebuilt to go from the left configuration to the right. Subsequent design iterations for the Block 1B tower have changed the EUS umbilicals and added a Vertical Stabilizer Damper above. Credit: NASA

An option once again to convert the current ML after the final Block 1 launch was ruled out by NASA. It would take up to a couple of years to complete, causing further impacts on SLS’s already lethargic launch cadence. Instead, the decision was made to build another Mobile Launcher dedicated to the Block 1B rocket.

The second Mobile Launcher (ML-2) has a cost estimate of $450 million. However, like ML-1, that cost is likely to rise over time based on the challenges involving ML-1, which ranged from being overweight to suffering from a slight lean. Both of these issues have since been resolved via engineering solutions.

ML-1 will host three launches, removing some schedule pressure on the readiness of ML-2, aided by Artemis 4 slipping to at least mid-2026.

NASA may then convert ML-1 into a second Block 1B capable launcher ahead of the required launch cadence for SLS during the mission to Mars in the 2030s.

Hardware for ML-2 has already begun to arrive at KSC this year, ready to make up the complex arrays of umbilical lines and Ground Support Equipment.

VSPs for ML-2 arriving in the VAB – via NSF L2

Hardware that has arrived at KSC for ML-2 includes the Vehicle Support Posts (VSPs). Each of SLS’s two Solid Rocket Boosters requires four VSPs, the primary structural interfaces between the rocket and the ML.

Each is 1.5 m (60 inches) tall with a base of 1.09 x 1.24 m (43 x 49 inches), made of cast steel with walls 10 cm (four inches) thick.

A milestone arrival in recent days was the Exploration Upper Stage Umbilical (EUSU), to provide commodity connections to the Exploration Upper Stage (EUS).

This is being installed at the Launch Equipment Test Facility (LETF), located just south of the Operations and Checkout (O&C) Building at the famous spaceport.

The famed facility at KSC has a deep history ranging back to the early Shuttle days. It tests launch-critical ground support systems and equipment.

It has also been involved with cryo testing for the defunct X-33 technology demonstrator for the VentureStar program and had a role in testing Delta IV ECS umbilicals and Centaur Upper Stage rolling beam tests.

At the heart of the LETF is the Vehicle Motion Simulator (VMS), utilized to emulate all the movements a rocket makes as it is rolled to the launch pad, and more importantly through the first 30 milliseconds of flight.

This allows exact simulations of the force and conditions the umbilicals and other launch equipment must work in to become qualified for use. Procedures and clearances can also be evaluated using the VMS.

Part of the LETF during ML-1 testing – via NSF L2

The LETF received several upgrades ahead of its role with SLS and Orion – while also offering its services to commercial companies per KSC’s Multi-User Spaceport initiative.

However, the construction of the ML-2 tower is still on hold after near-term funding for the project ran out in recent months.

Issues were cited early in the process via a GAO report which noted: “COVID-19 created inefficiencies and disrupted collaboration, experiencing delays receiving data from the SLS program that the project needs to inform the design of ML-2, and other related design development inefficiencies.”

Work has since ceased on the tower, past already planned work on the umbilicals, as confirmed by a NASA statement to

“The ML-2 contractor has paused some procurements in order to align with the near term (FY21/22) funding profile. Tower and Umbilical work is slated to start in FY22 and ’23. All the planned work will still take place, but the schedule is currently being reworked to ensure it will be completed within the allotted budget.”

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