SLS Mobile Launcher set for debut trip to Pad 39B in mid November

by Chris Bergin

The Space Launch System (SLS) Mobile Launcher (ML) will make its debut Crawler Transporter (CT) trip to Pad 39B later this month. Several week’s worth of testing will be conducted – including a visually dramatic fire suppression deluge test – as part of its development towards an eventual role of hosting crewed launches to Mars.

SLS ML’s History:

Formerly the Ares ML, the giant structure was constructed by Hensel Phelps of Orlando, Florida, following a $263 million contract award in May 2008, which included options including a second ML.

The ML was designed to specifically support Ares I and the vehicle’s associated Ground Support Equipment (GSE) from stacking in the VAB to launch out at Pad 39B.

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Evaluations into redesigning the launch mount and umbilical arms on the Fixed Service Structure (FSS) are ongoing – such as changing the “centerline” to that used by Saturn Vs, allowing for changes to the SLS’ configuration, such as the potential switch to liquid boosters in the 2020s.

Working via the Ares I “clean pad” design, the ML was designed to depart from the VAB, following the stacking and integration of Ares I, enroute for Pad 39B, where it would link up with the massive Roller coaster Emergency Egress System (EES) – an impressive structure which would have been based out at 39B.

Although 39B is now a clean pad, following the heartbreaking – but required – demolition of the former Shuttle Pad structures, the construction of the massive EES roller coaster is now understood to have been scrapped, with a slide tube escape system being considered.

The ML consists of the main support structure that comprises the base, tower and facility ground support systems, which include power, communications, conditioned air, water for cooling, wash-down, and was designed with ignition over-pressure protection in mind.

Hensel Phelps engineers worked on the structure at the mobile launcher park site area just north of the VAB, with trestles and girders arriving by barge in February of 2009, beginning the opening phase of work to create a base platform – one which is lighter than the current Mobile Launch Platforms (MLPs) which hosted the Space Shuttle.

With the giant Launch Umbilical Tower (LUT), the total weight of the structure is around 9.5 million pounds, compared to the 8.2 million pounds for just the Shuttle’s MLP.

Fabrication of the 345-foot LUT begin in May of 2009, in preparation for being placed on top of the ML’s platform as the LUT’s base, prior to the addition of nine additional sections via a giant crane at the build site.

The Installation of the first section was conducted on September 24, followed by a second section on October 15, a third on October 27, a fourth and fifth section in November, a sixth and seventh in December, followed by the final three sections, resulting all 10 sections being installed by January 28, 2010.

This was followed by the installation of the launch mounts – again, highly specific for only the Ares I vehicle – on the platform during the Spring of last year.

Crawler Transporter 2 (CT-2) then successfully relocated the giant Ares I Mobile Launcher (ML) to its new location at the East Parksite, where it was hooked up to utilities and power supplies at its new location. At that time the ML’s future was extremely bleak, following confirmation of Ares I’s cancellation.

The move was a success – as much as it was delayed by a few months due to problems with CT-1, resulting in the change of Crawlers for the move – with the ML showing no ill-effects from the move.

In fact, measurements during the short trip showed the ML actually weighed slightly less than expected, after initial fears late redesigns had added a worrying amount of mass to the structure.

While studies considered several ideas for hosting SLS during the latter part of its launch flow, the potential use of the ML also drew the attention of ATK, who’s “stick-like” Liberty Launch Vehicle concept is built around using the ML due to the matching aft configuration with Ares I.

Should SLS and Liberty both find themselves fighting over the ML, SLS will win out, with the need for a second ML, likely utilizing a former Shuttle MLP to save on costs, being allocated for Liberty.

All presentations and documented notes in recent months show SLS hosted at the former Ares ML.

ML’s Big Day Out:

After being parked up for over a year, the ML is set to take its longest journey this month, as managers finalize their assessments for taking the massive structure out to Pad 39B.

“Provide impact assessment for performing a move of the ML to Pad B approximately November 16,” noted an expansive overview presentation acquired by L2. “Move is achievable in timeframe mandated. Structural and functional engineering tests will be accomplished.”

Four key tests will be involved, relating to the structural response of the ML during rollout, structural clearance, HVAC (Air Conditioning) pressurization, and Tower Fire Suppression testing. The ML will be powered up via the pad 

Following a media event whilst at the pad, the return trip will also involve structural testing, conducted during and after it returns to the park site.

“Safety and Quality (NASA and Contractor) reviews will be conducted for the following procedures: ML Move from East Park Site to CX39B Pad Surface. Pad Surface Fit Check Utility Hook ups/Access. Fire Protection System Test flow through egress sprinkler heads. Fire Protection system flow through end of pipe in elevator room,” added the presentation.

Currently, the Atlas V launch with the Mars Science Laboratory is scheduled to take place on November 25, meaning the ML will be out at the pad during launch.

References in the presentation does not specify the relevance to being at the pad during the launch, as much as it may relate to how the tower reacts to a Cape launch whilst in situ, along with standard requirements to be “pad clear” during the Atlas V’s launch from SLC-41 less than four miles away.

“ML move will occur based on the above plan as long as MSL launch remains scheduled to occur prior to December 5th. In the event the scheduled launch date of MSL moves to no earlier than the week of December 5th, the ML move will be rescheduled to occur during the week of November 28th,” added the presentation.

“Should the launch date of MSL move after the ML is at the pad, a separate media event will be scheduled, date TBD. Current launch window for MSL opens on 11/25 and closes on 12/18. All personnel will be required to evacuate the launch pad on the date of the MSL launch.”

In total, the ML can look forward to a month’s worth of activities, highlighted by the trips on top of the Crawler Transporter, and the Fire Suppression deluge test, which will see the structure and tower – as depicted in the presentation – mirroring the Apollo ML water deluge test in March, 1966.

It is likely the media event will take place before and during this test, which will see water splashing out of several levels of the LUT.

Once returned back to the park site, the schedule shows the ML will receive a new coating of paint – required to protect the structure from the space coast’s corrosive salty air – due to begin in mid-December.

(Images: Via L2 content, driven by L2′s new SLS specific L2 section, which includes, presentations, videos, graphics and internal updates on the SLS and HLV, available on no other site. Other images via NASA.)

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