PRCB managers recommend Atlantis and Endeavour become SLS donors

by Chris Bergin

NASA managers have further refined their plans to transfer Orbiter and Ground Support Equipment (GSE) Main Propulsion System (MPS) hardware to the Space Launch System (SLS). Known as hardware retention, the plan now calls for Discovery to remain untouched, while Atlantis and Endeavour would donate their “inners” to play a key role in the development of the SLS.

SLS Development:

With all related centers and contractors noting a significant ramp up in planning for SLS – now that it has finally been announced by NASA’s top brass – the development phase will be key to ensuring the mistakes of the Constellation Program (CxP) are not repeated.

CxP claim their problems were related to a lack of promised funding, although continual changes to the baseline design and integration between the Ares I first stage and the Orion capsule – from very early in the process – caused major impacts to the schedule milestones.

NASA managers know such a repeat would likely result in SLS being the last vehicle they’d ever gain political support to build.

Thankfully – from a design standpoint – the SLS is utilizing a lot of commonality with the esteemed Shuttle engineering arm, utilizing a workforce which is fully focused on vehicle engineering, as opposed to the CxP days, when Shuttle was still the priority and hosted the majority of the hardware skillset, leaving CxP noticeably short in that department.

While the SLS’ heritage from both CxP and Shuttle are obvious – via the likes of the “External Tank” core, J-2X driven Upper Stage, and initially the Solid Rocket Boosters (SRBs) – the aft of the SLS relies on the power which was very specific to the Shuttle orbiters.

Initially three RS-25Ds will – along with the boosters – provide the thrust to launch the giant vehicle uphill, prior to five engines – by that time moving to the expendable RS-25Es – providing part of the evolvability of the SLS.

Given the commonality with the SSME’s partner in crime, the orbiter MPS, engineers felt it would be a waste of valuable, flight proven, hardware to send it out on display (as much as it won’t be visible) with the rest of the orbiters – when they head to their retirement homes.

This led to a study into removing the orbiter’s array of plumbing, allowing for it to be donated to the SLS development program.


Following a Program Requirements Control Board (PRCB) meeting this month, those plans have been refined, to the point of an overall approach and associated costs, along with the impacts such work would add to what is known as the Transition and Retirement (T&R) phase for the orbiters.

“The purpose of this (review) is to identify both specific and general guidelines to be followed in the preparation (work paper generation) and execution of the removal of Main Propulsion System hardware from the Space Shuttles in support of SLS,” noted one of three PRCB presentations on the effort (all available in L2).

“Potential Cost and Schedule mitigation option for SLS. MPS component development can pace the overall core stage schedule. Retaining and utilizing SSP MPS hardware can have large initial cost savings.

“Beyond the existing Transition & Retirement (T&R) plan: Acquire high value items from the Orbiters, LRU (Line Replacement Unit) spares, GSE, Tooling and Documentation. SLS is needing hardware to support a test program and first two flights. Core Stage Option Utilizing Shuttle MPS. RS25 Engines. MPS. TVC (Thrust Vector Control) and Avionics.”

The initial plans involved all three orbiters. However, following an opening evaluation into the best path forward, Discovery won’t be donating any hardware – other than the three SSMEs which flew on her final mission (STS-133).

It is not documented as to why this decision was made – although it would match the shuttle extension studies, which concluded Discovery would be retired, allowing Atlantis and Endeavour to continue with additional flights.

This was partly based on Discovery being due for her Orbiter Modification Down Period (OMDP), which would have likely involved work on ‘areas of interest’, such as the MPS feedline ball struts and VJ annulus on the LH2 side and all the MPS components. Previous engineering notes did reveal small cracks in the ball strut.

Further checks – along with a high level of protection – will be provided on all MPS hardware to be removed, now specific to Atlantis and Endeavour, as the PRCB documentation outlined.

“All SLS-hardware is to be maintained ‘flight like’. The term ‘flight like’ is defined as follows: Parts will be maintained visibly clean, appropriately handled/transported, and maintained in good working condition. Part cleanliness shall be maintained using best shop practices: Cleanliness will be maintained via work in an environmentally controlled atmosphere.”

This relates to the Orbiter Processing Facility (OPF) maintaining purges as appropriate, using double clean bags/tape/caps/plugs to secure open ports/lines, and undertaking a best effort to maintain an acceptable level of cleanliness using field expedient techniques if work is to be performed in an uncontrolled environment, such as the Vehicle Assembly Building (VAB), where the orbiters are taking it in turns to visit.

“Field cleaning of MPS parts/tooling using approved cleaning materials/fluids is acceptable. Parts obstructing removal of MPS components such as pneumatic tubes, clamps, brackets etc., are not required to be re-installed but shall be recorded in a list of removed parts within the Work Authorization Document,” added the presentation.

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“All removed parts will be identified by part number, part description, and serial number (when readily identifiable). Cosmetic discrepancies (not affecting fit/form/function) of the part do not require Squawk (issue) initiation, but shall be noted/documented during the part final inspection results.”

All of the removed MPS hardware would then be placed into storage at the Assembly & Refurbishment Facility (ARF), which also includes the large GSE equipment used on the orbiter MPS, which is currently located in the NSLD (NASA Shuttle Logistics Depot) at the Kennedy Space Center (KSC).

“Preserve Shuttle Heritage MPS Hardware for SLS Opportunities: Put a Hold on Retired Shuttle MPS, TVC and Avionics Assets. Remove & Store Critical Orbiter MPS, TVC and Avionics Components at the ARF. MPS components are the most critical – saving cost and schedule,” added another presentation.

“Develop cost and schedule impacts to remove & store existing orbiter hardware. Develop cost to retain all MPS, TVC and Avionics related LRU spares and sub-assemblies at the KSC logistics warehouse. Develop cost impacts to retain all MPS GSE, tooling and component documentation from NSLD.”

The ARF is under the control of the Marshall Space Flight Center (MSFC), while some hardware will also take up residency at KSC’s Logistics Warehouse.

“Remove high value MPS, TVC and Avionics hardware from the aft compartment of orbiters prior to sending them to museums. Package, transport and store the hardware in the Assembly Refurbishment Facility. Floorspace is available to store hardware in an environmentally controlled area,” the overview continued.

“NSLD Bld 3 MPS Test equipment, special tooling and servicing documentation. Building needs to be restored to original configuration and GSE needs to be removed ASAP. Maintain Spare MPS, TVC and Avionics components, subassemblies and parts at the KSC Logistics Warehouse.”

While long lists of specific hardware and costings are noted, two different schedules are shown, one showing no delay to the final departure of the orbiters to their exhibitions, while another shows a seven month impact for Endeavour’s trip to the West Coast, and a 12 month slip to Atlantis’ trip up the road to the KSC Visitor Center.

Regardless, no official dates have been confirmed, even with Discovery, who’s role with the SLS is now no longer required, ahead of the Shuttle Carrier Aircraft (SCA) ferry to the Smithsonian.

“The Museum is working closely with NASA to determine the schedule for delivery of Discovery and removal of Enterprise from the Museum’s Steven F. Udvar-Hazy Center. No date has been set,” noted Isabel T. Lara, Media Relations at the Smithsonian National Air and Space Museum, adding their timeline closely involves Enterprise, as she would have to be moved to make way for Discovery.

“The tentative plan calls both spacecraft to be moved over the course of a few days. Enterprise is expected to be on display until Discovery arrives to replace it.”

Enterprise will eventually be taking up residency in New York City.

If the new plan can avoid impacts to the T&R timeline – as may now be the case with only two orbiters involved – all associated facilities will also be released on a nominal timeline. However, if the additional T&R impact becomes the reality, the slip is significant, per the documentation.

“OPF-1 remains occupied for an additional 17 months. OPF-2 remains occupied for an additional 7 months. Logistics remains occupied for an additional 17 months. Release of MDD (Mate Demate Device) delayed ~7 months. Overall completion of T&R delayed 8.5 Months.”

In conclusion to the documentation, the PRCB noted they are in a position to green light the MPS donation, with the final approval likely to be forthcoming in the coming weeks – following the conclusion of the ongoing hardware inspections and planning.

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“Recommendation: Approve CR (Change Request) to remove MPS, TVC and Avionics hardware from orbiters and store at the ARF. Concur with Plan to remove transport MPS component GSE tooling and Documentation from NSLD and store at the ARF. Concur with plan to maintain orbiter MPS, TVC and Avionic spares at the KSC logistics Warehouse.”

(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. Other images via NASA and Larry Sullivan, Chris Gebhardt (MaxQ Entertainment/ orbiter engineering tour video (1000mb) available on L2.)

(L2 is – as it has been for the past several years – providing full exclusive SLS coverage, available no where else on the internet. To join L2, click here:

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