NASA outlines SLS Mobile Launcher umbilical plans

by Chris Gebhardt

Continuing toward a debut of late-2017, NASA’s Space Launch System (SLS) rocket is one step closer to that ultimate goal as the U.S. space agency continues to baseline the plans for the umbilical arms and connections to the new Heavy Lift Launch Vehicle (HLV) from its Mobile Launcher (ML).

SLS umbilicals and launch accessories:

As part of NASA’s Ground Systems Development and Operations division for the new SLS rocket and its associated systems, the first in what is certain to be a series of reports and presentations regarding the Mobile Launcher (Mobile Launch Platform and service tower) for SLS has been acquired by

Available for download on L2 (Link), the presentation details the already baselined as well as “proposed, not budgeted” umbilicals and launch accessories for SLS.

In all, the presentation indicates a total of eight umbilicals for SLS: the Launch Abort System ECS, the SM Umbilical 1 (for ECS and Avionics), the iCPS (Interim Cryogenic Propulsive Stage) Umbilical, the Core Stage  (CS) Intertank Umbilical (for CS avionics and gaseous hydrogen venting), two Tail Service Masts (TSMs), and two Aft Skirt Umbilicals (for the Solid Rocket Boosters).

Additionally, four baselined access arms will be required and utilized for the SLS: the Crew Access Arm, the Service Module access arm, the iCPS access arm, and the CS Forward Skirt access arm.

In terms of currently proposed but-not-yet-budgeted items, the presentation lists the CS Forward Skirt Umbilical (for ECS, electrical, and three fluid Quick Disconnects) and one CS Intertank access arm.

ML structural modifications:

In an effort to streamline costs and utilize as many hardware elements possible from the now-defunct Constellation Program, the Mobile Launcher (ML) originally built for the Ares I Crew Launch Vehicle (CLV) will be reconfigured and modified to accommodate the much-larger SLS vehicle.

According to the Ground Systems Development and Operations document, the modification design period, which began on 9 April 2012, is tasked with developing “the Design Criteria and a Modification Plan to convert the CLV ML to be used for the SLS launch vehicle.”

These modification plans include, to date, the modification of the base of the ML to accommodate the SLS rocket.

This will include “reframing a new vehicle exhaust hole whose centerline location provides additional clearance from the existing ML tower as compared to the original CLV ML layout.”

The majority of the modification work for this requirement will take place, on the ML between the already-present CLV ML girders and trusses.

Moreover, since the SLS rocket’s pad footprint is vastly different from that of the Ares I CLV’s, a new footprint design for the SLS’s support posts and ML 0-level umbilicals will be required.

This will necessitate structural changes to the ML base. “Add new ML base compartments as needed to provide space for facility systems and GSE and relocate facility systems within the ML base to accommodate the new exhaust hole layout,” notes the Ground Systems Development and Operations presentation.

Furthermore, the Ares I CLV-mandated Ignition Over-Pressure (IOP) and Deck Quench Water Systems will no longer be required in their current configuration.

A new Sound Suppression system will need to be added to the ML as well.

Relocation and addition of these items will be based around the eventual redesign and confirmation of the placement of the new vehicle exhaust holes and pad flame deflector location.

HVAC and electrical trays on the ML service tower will also need to be relocated and fortified to accommodate (survive) the acoustic energy environment produced by the massive three/four/five engine, twin 5-segment SRB SLS vehicle.

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Finally, the ML’s ground power interfaces will need to be realigned to accommodate structural/umbilical changes in the VAB (Vehicle Assembly Building), at Pad 39B (SLS’s sole launch pad), and at the ML park site located north of the VAB.

Analysis review #2 of ML upgrades is already underway, with a Quality Control check scheduled for 8 February 2013 ahead of final submittal of the modification plan on 28 February 2013.

Tail Service Mast Umbilicals:

With the ML base redesign in work, analysis and development of SLS’s support umbilicals is also underway.

With respect to the fueling and draining of the Core Stage (CS) for SLS, two Tail Service Mast Umbilicals (TSMUs) will be required – one for the Liquid Oxygen and one for the Liquid Hydrogen fuels to be used by SLS.

As noted by the presentation, “The ML shall provide T-0 tail service umbilical mechanisms to the Core Stage aft for liquid oxygen (LO2) and liquid hydrogen (LH2) fill and drain and other services.”

The TSMUs will leverage existing tilt-up designs from the Apollo era, weigh a combined total of 120,000 lbs, and provide electrical power to the SLS CS during VAB and pad processing.

Use of the tilt-up TSMU design had already been approach, making  moot any further work on salvaging the TSMs from the three Space Shuttle MLPs (Mobile Launcher Platforms).

“New Tilt-Up TSMs will retract in Vehicle rise off time and can be made compatible with SLS Launch environment,” notes the Ground Systems Development and Operations presentation.

Both LH2 and LO2 TSMUs will be located on the same side of the vehicle – on the south side of the ML, opposite the umbilical tower.

Initial baseline configuration models indicate that the TSMUs will be placed +/- 12.7 degrees from Center Line (CL) with respect to the north/south CL of the vehicle – with the LO2 umbilical in the south west location and the LH2 umbilical in the south east location.

TSMU elevation angle to reach the fill and drain ports on the CS of SLS is currently predicted to be 200.48 degrees.

Access to the TSMUs will be from the ML Zero Deck, A Level Room AB8, and TSMU external work platforms – specifically for umbilical mate operations in the VAB.

Orion Service Module Umbilical:

In addition to crew access to Orion, an Orion Service Module Umbilical (OSMU) will provide electrical, data, and purging processes to Orion’s Service Module.

Weighing approximately 40,000 lbs, the OSMU will be 27 feet long, 17 feet wide, and 42 feet tall (including the OSMU safe house to protect it from the intense, SRB-induced launch environment).

“The OSMU is a T-0 umbilical mechanism providing GSP, Environmental Control System (ECS), GCS, BAIR, LCS, and GN2 to the Orion Service Module (SM),” notes the presentation.

Release of the OSMU will be triggered at T-0 (SRB ignition) by a signal to the release mechanism on the ground umbilical plate.

At this point, the OSMU truss boom structure will tilt-up into its safe house on the ML umbilical tower. This truss boom structure (arm) will reach out toward but remain 16 feet shy of the Orion Service Module itself.

The 16-foot gap between the OSMU truss boom structure and Orion Service Module will be bridged by draped umbilicals terminating at a ground umbilical plate that will serve as the actual T-0 umbilical to the Service Module.

Access to this ground umbilical plate will only be provided inside the VAB – meaning the umbilical plate will be inaccessible once the SLS rocket is rolled out to LC-39B for launch.

An ECS umbilical to the LAS (Launch Abort System) will also extend out from the OSMU to the LAS Ogive (roundly tapered end of any three-dimensional object) cavity.

Aft Skirt Umbilical:

For SLS’s twin SRBs, two Aft Skirt Umbilical (ASU) units will provide electrical, GN2 purge, and data connections to the boosters during processing and countdown operations.

As stated by the Ground Systems Development and Operations presentation, “The ML shall provide a T-0 Ground Carrier Assembly umbilical to the SRB Aft Skirt for SRB joint heaters and SRB instrumentation and a T-0 GN2 SRB Aft Skirt purge mechanism.”

These ASUs will be rise-off umbilicals based on a legacy system initially designed for the SRB joint heaters during the Space Shuttle Program.

Each ASU will weigh approximately 3,700lbs and be 65 inches tall, 37 inches wide, and 37 inches deep.

Interim Cryogenic Propulsive Stage Umbilical:

Weighing in at 100,000lbs, the Interim Cryogenic Propulsive Stage Umbilical (iCPSU) will be a T-0 umbilical for SLS providing “LH2 fill/drain, LO2 fill/drain, GH2 vent, GSP, ECS, GHe (gaseous helium), HGLDS, LCS, RSCS, FSS, and GN2 to the SLS Upper Stage Interim Cryogenic Propulsion Stage (iCPS).”

Mated to the vehicle in the VAB, the iCPSU will contain a ground umbilical plate that will provide the physical attachment point to the SLS vehicle. Access to the ground umbilical plate will only be possible in the VAB.

At the termination of countdown operations, a T-0 release command will be sent to the iCPSU, initiating a swing arm-style retraction of the iCPSU out of SLS’s liftoff flight path.

The iCPSU arm itself will consist of a truss boom structure terminating 10 feet from the SLS rocket, with the remaining distance covered by five (5) draped umbilicals.

The iCPSU T-0 umbilical interface is currently baselined from that of the Delta IV rocket’s 5m second stage. Thus, the swing arm umbilical is currently designed from the profile of that used by the Delta IV rocket.

In an effort to reduce cost as much as possible and use already proven hardware, the iCPSU arm will use the GOX vent arm hinge used for Space Shuttle launch operations on LC-39B. All latchback, shock absorbers, and work platforms from the GOX vent arm at LC-39A will be used as well.

Access the iCPSU arm will be provided via the 220-foot or 240-foot level platforms of the ML umbilical tower.

Core Stage Inter-Tank Umbilical:

Originally intended to be a reuse of the Space Shuttle External Tank’s Ground Umbilical Carrier Plate (GUCP) and vent line, an April 2012 Technical Interchange Meeting (TIM) for SLS’s Core Stage revealed a “significantly larger” Inter-Tank umbilical plate design than originally anticipated.

Thus, reusing Shuttle-era technology for the Core Stage Inter-Tank Umbilical (CSITU) was rendered “not feasible.”

According to the Ground Systems Development and Operations presentation, “Final cost and schedule impacts to … baseline for change from ET Vent Line reuse to new swing arm umbilical” are pending final approval.

The new design now features the CSITU as another swing-arm T-0 umbilical, providing commodity services to the SLS’s Core Stage Inter-tank region.

The umbilical arm will be 45 feet in length, 8 feet in width, and 15 feet in height.

The umbilical and ground carrier plate will be mated in the VAB – with no pad access for umbilical mating – and remain connected to the vehicle until liftoff.

Umbilical plate size is now expected to be 34 inches x 54 inches.

Core Stage Forward Skirt Umbilical:

An umbilical that could come to fruition but is not currently in the ML umbilical tower’s baseline design is the Core Stage Forward Skirt Umbilical, or CSFSU.

Proposed as a way to provide purge and “other services” to the SLS’s Core Stage Forward Skirt (CS FS), the CSFSU would be a T-0 umbilical requiring VAB access for mating of the umbilical plate to the SLS rocket.

Commodity lines for the CS FS would run through the stabilizer truss of the umbilical arm, with drape commodity lines extending from the arm to CS FS attach location.

The proposed umbilical plate would be 46 inches x 34 inches.

Vehicle Stabilizer:

In a departure from NASA’s immediate predecessor to SLS, a Vehicle Stabilizer (VS) will be used during rollout, launch pad, and pre-launch operations for the SLS rocket.

In short, the SRB hold-down posts will not be enough to completely and safely stabilize the SLS rocket during rollout and pre-launch pad operations.

“Pre T-0 release stabilizer with non-active damping capability incorporated in the actuators” will allow for stabilization loads of up to 50,000lbs in a side-to-side swaying motion and 200,000lbs in an in-out toward tower swaying motion (peak sway of less than 1 ft/s) of the SLS rocket.

The VS will be attached at two locations to the SLS rocket, 2,350 inches (156.6 feet) up the side of the rocket at the 135-degree and 225-degree locations around the circumference of the Core Stage.

As stated by the presentation, “VS conceptual design being driven to a T-0 release mechanism. Design team initial concept incorporates a hard lock and soft lock actuation system that allows the hard lock to be disengaged prior to T-0 without disconnection.”

The capability would then exist to reengage the hard lock in the event of a subsequent launch scrub/abort.

Due to ML design constraints, it is possible that the VS and CSFSU will be combined into one umbilical in the final design phase.

Crew Access Arm:

Currently anticipated to use existing hardware leftover from the Space Shuttle Program, the SLS’s Crew Access Arm (CAA) will use the truss structure of the Orbiter Access Arm from LC-39A.

However, this reuse of the OAA from LC-39A is now in doubt after the passage of an Engineering Review Board plan to fabricate a new truss arm to incorporate electromechanical control.

Regardless of a truss reuse or new fabrication, all CAA hinge actuation systems and latchbacks will be new, as will the “Environmental Chamber (EC)” from which the crew will board the Orion capsule.

The CAA will be 67 feet long, 10 feet wide, and 18 feet tall and will include a lower level for access to the Service Module.

The CAA is currently expected to weigh approximately 74,000lbs and will connect to the ML umbilical tower at the 270-foot level, with access from the 260-foot level.

Considerations will also include the Emergency Egress System (EES), that may include a roller coaster at the Pad.

Vehicle Access Arms:

In addition to the CAA, two Vehicle Access Arms (VAAs) will be required to properly service the SLS rocket for launch.

With each arm weighing roughly 50,000lbs, the VAAs will “provide processing personnel access to iCPS for hypergol servicing. Core Stage Forward Skirt access also proposed for LRU (Line-item Replace Unit) change-out.”

These LRUs would primarily consist of avionics components.

However, these VAAs might not be necessary once the design process of SLS is complete.

Vehicle Support Posts:

Finally, the Ground Systems Development and Operations document showcases the Vehicle Support Posts (VSPs).

Designed to “Provide 8 Vehicle Support Posts for SLS Boosters using as-designed Ares 1 stationary VSPs, utilizing Shuttle Hold-down Post blast shields, bushing, spherical bearings, and shoe retainers,” the VSPs will be 68 inches tall, 43 inches wide, and 49 inches deep.

The VSPs will provide structural load support of the SLS rocket through the Solid Rocket Boosters.

Currently, it is expected that the VSPs will be static, providing a weight-of-vehicle-only support pedestal for the SRBs – with a Ground Support Equipment bolt inserted through the VSPs and SRB for rollout operations stability only.

For comparison, the corresponding component for the Space Shuttle saw the support posts provide hold-down support for the Shuttle vehicle, terminating at T-0 with the detonation of NASA Standard Detonators to explosively severe the hold-down bolts and free the Shuttle’s SRBs from the pad.

While the SLS’s Vehicle Stabilizer would most likely negate the need for active hold-down support from the VSPs, the presentation does note that “Vehicle loads analysis may require addition of ‘hold-down’ requirement, even with base-lining of Vehicle Stabilizer.

“Vehicle height requirement & launch drift may exceed VSP as designed height or have drift interference. Due to reduced drift of SLS vs. Ares I, Shuttle HDP (Hold-Down Posts) may be used in place of VSP.”

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