NASA’s Space Launch System (SLS) rocket completed another milestone on its way to launch with the Umbilical Release and Retract Test (URRT). The URRT was performed on the rocket on September 19 while it stood in High Bay 3 of the Vehicle Assembly Building (VAB).
During the test, the swing arms and T0 umbilicals at the base of the rocket were commanded to retract from the vehicle as they will during a standard SLS launch countdown.
The test occurred on Mobile Launcher 1 (ML-1) and allowed ground teams to verify and validate the mechanisms, timings, and function of the umbilical release and retract system that will separate and move the arms — that support data and communications pathways as well as fueling ports for the upper stage — away from the SLS rocket and against the tower at launch.
The tower itself is built onto ML-1 and supports not only the swing arms and their data and fueling systems, but also the Orion capsule and Service Module with purge lines, data and communication paths, and access to the Orion vehicle for crewed missions.
This is the same Mobile Launcher that will be used for the Artemis 1 mission and other flights that use the Interim Cryogenic Propulsion Stage (ICPS). It was initially constructed for Ares I in 2010, but with the cancelation of the Constellation program, ML-1 was modified to be used with SLS Block 1 with the ICPS.
NEW FOOTAGE
Watch as the different platforms around the SLS rocket retract as part of the Umbilical Release and Retract Test (URRT) at @NASAKennedy. @NASAGroundSys conducted the test to prepare for future #Artemis I stacking and launch activities >> https://t.co/HNSKsaXf8c pic.twitter.com/IV8MrSwrYn
— NASA_SLS (@NASA_SLS) September 22, 2021
Following Artemis 3, NASA will move to a different launch tower, ML-2, that will support the launches of SLS Block 1B and its Exploration Upper Stage that replaces the ICPS.
Aerospace & Defense
(adsbygoogle = window.adsbygoogle || []).push({});
A second Mobile Launcher is required as a modification of ML-1 was not feasible because it would result in more than two years between SLS launches.
Regardless of which ML is used, the SLS rocket has a variety of umbilicals that are attached to different parts of the ML tower.
The first SLS standing tall on its Mobile Launcher ahead of its Umbilical Release and Retract Test (URRT) — a critical step toward launch. (Credit: NASA/Frank Michaux)
At the bottom of the rocket sit the Aft Skirt Electrical Umbilicals (ASEU), which provide communication to the Solid Rocket Boosters (SRBs) and communicate with the Launch Release System to issue the final release command.
Also connected to the aft skirt are the GN2 Purge Umbilicals, which are used to purge the SRB aft skirts.
Both of these were not involved in the URRT.
A final set of ground umbilicals at the base of SLS are the two Tail Service Mast Umbilicals (TSMUs). These service masts are the primary connection to fuel the rocket’s Core Stage with liquid hydrogen coming from one of the TSMUs and liquid oxygen from the other.
They are located on the opposite side of the rocket in relation to the launch tower. The TSMUs were involved in the URRT.
Moving up the rocket, the Core Stage Inter-Tank Umbilical (CSITU) is connected to the Core Stage intertank between the hydrogen and oxygen tanks at a height of 42.7 meters.
This arm is used to vent gaseous hydrogen from the Core Stage, provide a data connection, and supply pressurized gases and power.
The Core Stage Forward Skirt Umbilical (CSFSU) is above at 54.9 meters between the first and second stages right above the oxygen tank. It is used to provide GN2 (gaseous nitrogen) to the SLS core stage.
Six meters above that is the Vehicle Stabilizer System (VSS). This is used to stabilize the core stage during rollout and countdown and will drop down right before liftoff.
A side view of SLS with the SRB cable trays exposed and additional, temporary wiring for the modal test sequence visible. The cable trays will eventually be closed out and covered for flight. (Credit: NASA/Frank Michaux)
Above that, at the 73.2-meter level, is the support umbilical for the second stage and the RL10B-2 vacuum engine. This is the Interim Cryogenic Propulsion Stage Umbilical (ICPSU) and provides liquid oxygen and liquid hydrogen fueling support for the upper stage as well as electrical connections and pneumatics.
Even higher, next to the Crew Access Arm sits the Orion Service Module Umbilical (OSMU), which was also included in this test. It provides liquid coolant and purge air for the environmental control system and the Launch Abort System.
In this test, the OSMU was connected to the Orion Mass Simulator at the top of the stack. The actual Orion was purposefully left out of this test sequence to allow as much time as possible for the rideshare CubeSats that will fly with it to be readied for flight.
All of the swing arm umbilicals run on different forms of detachment mechanisms, using winches, wire rope lanyards, or even breakpoints. Most of them are not only built with one but two or even three different mechanisms that can detach the umbilical.
None of the swing arms use pyrotechnic separation systems as previous NASA rockets have.
The mechanisms to release the umbilicals will be triggered by the same signal used to give the start command to the two SRBs to make sure the rocket has a clear path upwards when the boosters ignite since the launch cannot be aborted after that command is given.
Numerous other elements of ML-1 and its tower’s fueling, communication, data, and associated systems were tested at Launch Complex 39B prior to SLS Artemis 1 stacking in an effort to find issues that could be corrected before first flight operations and prove out the ground architecture for SLS.
Part of that pad test simulated the countdown and an Umbilical Arm Simultaneous Retract Test involving the ICPSU, CSFSU, and CSITU.
With the URRT now behind them, teams will now prepare for the full stack’s Integrated Modal Testing (IMT). The rocket will be tested with mechanical shakers to check its structural integrity and resonance frequency.
The SLS Mobile Launch, a hold-over from Constellation, on a modified Apollo-era crawlerway transporter arrives at LC-39B for testing. (Credit: Stephen Marr for NSF/L2)
This will be one of the last tests with the Orion Mass Simulator before it will be de-stacked and replaced with the Orion spacecraft and service module for the Artemis 1 mission.
The SLS rocket is currently planned to roll later this year to Launch Complex 39B for a full Wet Dress Rehearsal. After that, it will be brought back to the VAB for final checkouts and ordnance installation.
As of Tuesday, September 21, NASA is still holding to a public target of the end of the year for Artemis 1’s launch; however, early 2022 is a far more likely launch target at this time.
(Lead image: SLS in VAB High Bay 3 ahead of its Umbilical Release and Retract Test. Credit: NASA/Frank Michaux)
