SLS Tail Service Masts undergoing construction ahead of LETF testing

by Chris Bergin

Engineers have begun the construction of two huge Tail Service Masts that will play a crucial role with the Space Launch System (SLS) on launch day. The TSMUs (Tail Service Mast Umbilicals) will be tested on the Vehicle Motion Simulator (VMS) at the Kennedy Space Center, before being installed on the deck of the Mobile Launcher (ML).


As preparations continue for the maiden flight of the Space Launch System (SLS) in late 2018, work is progressing on the array of umbilicals that will provide the lifeline between the rocket and the Mobile Launcher (ML).

Numerous devices are already deep into their test phase, which is being conducted at the Launch Equipment Test Facility (LETF) inside the Kennedy Space Center grounds.

2016-05-17-175629April marked the first views of the new TSMUs (Tail Service Mast Umbilicals), two of which will be installed on the zero deck of the Mobile Launcher.

The photos (L2 SLS) provided an insight into their size, although it’s their deep history with NASA rockets that have provided the guidance towards their design role with SLS.

Three TSMs were involved with Saturn V rockets, while two TSMs were installed on the Mobile Launch Platforms (MLP) during the Space Shuttle era.

For Shuttle, the TSM hosted a carrier plate that was mated to either side of the orbiter during stacking operations inside the Vehicle Assembly Building (VAB). The plate was the conduit for a large number of umbilicals carrying cryogenic propellant, along with gases lines and an array of electrical connections.

They performed well during the history of Shuttle, although historical documentation references a high level Tiger Team investigation into a close call incident during STS-112, where a faulty connection between Atlantis and the T-0 umbilical panel inside the TSM almost resulted in a launch where the explosive holddown bolts on the Solid Rocket Boosters didn’t fire.

Former Space Shuttle Program Manager Wayne Hale explained the event in 2012 blog post.

Subsiquent improvements in the system will feed into the design of the SLS TSMU, which will first undergo a large amount of testing at the LEFT.

2015-07-07-141058The facility is equipped with a control room – allowing engineers to collate data and detect any hazardous conditions with the hardware undergoing testing. It also includes workshops and even its own High Bay – large enough to host the assembly of the large ground support structures.

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 umbilicals and other launch equipment must work in to become qualified for use. Procedures and clearances can also be evaluated using the VMS.

During the testing, The LH2 TSMU will be tested on VMS-1, while the LOX TSMU will be tested on VMS-2.

The SLS TSMs will use a pneumatic operated system to detach the umbilical plate from SLS, before retracting the umbilical carrier and closing the door to protect the umbiicals and connections from the exhaust of the SLS launch.

2016-05-17-175609*L2 Members click here for a video overview of all the SLS umbilicals overviewed and shown in action during a launch*

This is an advance on the Shuttle TSMs, which used a drop weight for the retraction, which was released via pyrotechnic devices.

Planning teams decided the pryo devices shouldn’t be used for SLS, which led to the decision to go to a pneumatic retraction system alternative.

Although the MLP-2 TSM carrier plates were removed back in January 2012, set to be reused for the SLS TSMUs, the program has decided to use totally new hardware on both the flight and ground side.

2016-05-17-220143With the TSMUs joining numerous other SLS ML elements for testing at the LETF, some key items will be installed directly on to the ML itself, without going through the test facility.

This includes the Crew Access Arm (CAA) which won’t be used by an Orion crew until the 2020s, given the Exploration Mission -1 debut of SLS will be uncrewed.

Also set to be installed on to the ML without going through the LEFT will be the Thrust Vector Control Hydraulics Support System (THSS). THSS will supply hydraulic power to test out the Thrust Vector Control systems on both Solid Rocket Boosters and the SLS Core after stacking in the VAB.

The Hydraulic Accessories Source Supply Pump (HASSP) is also awaiting installation on the ML. HASSP will supply hydraulic fluid to fill the accumulator banks in all four of the swing arms and provides hydraulic power to raise the Vehicle Stabilizer (VS) during mating operations in the VAB.

(Images via NASA and L2 SLS Sections. To join L2, click here: //

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