Vehicle of Record – SLS spares majority of Discovery’s storied MPS

by Chris Bergin and Philip Sloss

As engineers finalize the removal of Main Propulsion System (MPS) hardware from the retired Space Shuttle fleet – comprising of large elements of the orbiter’s “guts” that are being donated to the Space Launch System (SLS) program – Orbiter Flow manager Stephanie Stilson revealed that “her baby”, Discovery, has held on to most of her MPS, allowing her to retire as the “vehicle of record”.

Orbiter Donations To SLS:

In compliance with a decision by the all-powerful Program Requirements Control Board (PRCB) last year, engineers have been removing large pieces of hardware from the aft of the orbiters, allowing them to live on with the new Heavy Lift Launch Vehicle (HLV).

The hardware’s continued role with the SLS makes sense, allowing them to live on as part of the Integrated MLS with the monster rocket, which – with the orbiter – consisted of the Space Shuttle Main Engines (SSMEs), an external propellant tank (ET), a propellant management system used to transport fuel and oxidizer from the tank to the engines, and a multipurpose helium system.

SLS will be utilizing the remaining stock of Pratt & Whitney Rocketdyne RS-25Ds from the Space Shuttle Program (SSP), engines which are no strangers to the MPS components the orbiters are donating.

This could lead to a potential reunion between hardware from – for example – Atlantis MPS components and the three engines – ME-1 (2047), ME-2 (2060) and ME-3 (2045) – she last flew with during STS-135. While these donations will save money for the SLS program, the flight-proven hardware will provide confidence for the development of the new vehicle.

A total of 15 RS-25Ds are currently being transported – one at a time by truck – to NASA’s Stennis Space Center (SSC). Some will return in a few year’s time as part of a Battleship core for testing at the Kennedy Space Center (KSC), while some will fly on the opening couple of SLS missions – the first of which is scheduled for 2017, for an uncrewed test mission around the Moon – know as Exploration Missionm -1 (EM-1).

SLS will eventually move on to a cheaper, expendable version of the engine, known as the RS-25E.

During the PRCB deliberations, the requirements relating to how much hardware could be removed from the fleet – without heavily delaying their Transition and Retirement (T&R) flows – saw Discovery removed from the equation, leaving just Atlantis and Endeavour as the main SLS donors.

However, thanks to procedures that allowed for the effort to be conducted during the nominal T&R flow – and in some cases even during the orbiter’s vacation inside the Vehicle Assembly Building (VAB) – all three orbiters have been confirmed as donors.

During the recent dual rollover of Discovery and Atlantis, Orbiter Flow manager Stephanie Stilson revealed some extra details on the MPS donation effort, in an interview with’s Philip Sloss, including how Discovery has managed to keep a lot of the major MPS components – when compared to her sisters – allowing for her to retire as the “vehicle of record”.

“In some cases (on Discovery), they were valves, certain smaller components, as opposed to with Endeavour and Atlantis, it’ll be the larger components – the prevalves, the 17-inch lines, and so forth,” noted Ms Stilson.

“(There is) a lot more coming out of Endeavour and Atlantis than coming out of Discovery; when you look in the aft of Discovery, it still looks congested, there’s a lot of hardware in there, whereas when we finish with Atlantis and Endeavour, it’ll be pretty empty in there, (although) there will be some hardware still remaining.”

It’s no secret how much the KSC workforce love the orbiters, vehicles that were treated as living machines, allowing the teams to provide the care and attention that played no small part in the ability to safely complete their missions.

As such, seeing their “guts” pulled out of their afts is a bitter pill for the teams, as much as they understand the benefits for the future program.

Ms Stilson was quick to note she was happy “her baby” managed to hold on to more MPS hardware than had been initially expected.

“I was little bit torn, because like Smithsonian (Discovery’s retirement home) I wanted to see Discovery kept intact. Discovery is my baby (and) I didn’t want to see anything happen to her, but I’m also torn because I do want us to have the ability to launch that next vehicle as soon as possible.

“If using components off of the orbiters can help that happen, then we’re all for that, so I think we came to a good compromise in the sense of pretty much leaving Discovery as the vehicle of record. We didn’t take as much out of Discovery, but then we are taking out of Endeavour and Atlantis those components so that we can help SLS, so I think it was a good compromise between the programs.”

Discovery’s T&R flow is now complete, as she waits patiently inside the VAB, proudly waving her own flag from her nose gear, ahead of one final flight, this time atop of the Shuttle Carrier Aircraft (SCA) for the trip to the Smithsonian.

This is her final month in Florida, ahead of being rolled out to the Mate-Demate Device (MDD) at the Shuttle Landing Facility (SLF), prior to being mated atop of the SCA for the flight north. 

Endeavour – preparing for a trip to California, and Atlantis – which will remain at KSC at a specially constructed facility, are seeing their removed MPS hardware stored at the Assembly & Refurbishment Facility (ARF).

The large GSE (Ground Support Equipment) used on the orbiter MPS – currently located in the NSLD (NASA Shuttle Logistics Depot) at KSC – will also be preserved.

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.

“They will remain here in our logistics area until they get shipped to where the SLS program wants them,” added Ms Stilson. “I’m guessing it’ll go to Marshall, because it’s managed out of Marshall, but not exactly sure where they’re going to take them.

“We got started on some of the SLS components out of the aft (on Atlantis) – the smaller ones. The big ones have to be done here (in the Orbiter Processing Facility). So brackets (were) being removed, some of the valves and some of the smaller lines to get [those] out of the way so we can then get to the bigger components.

“It’s like working on your car – you’re doing something on your engine, you’ve got to get some of the littler things out of the way to get to the big things.”

Planning on the removal procedures for major parts of Endeavour’s MPS is being worked at this time, although initial removal work has already begun.

“We’ve been writing paper, (but) actually we’re starting some of the SLS work on Endeavour – that’s just been in the past week. (We’re) doing that work somewhat in parallel – we weren’t intending to do it in parallel, but it just kind of worked out that way,” noted Ms Stilson.

“So we’re kind of having folks bounce back and forth between the two vehicles.”

To read about the orbiters –  from birth, processing, every single mission, through to retirement, click here for the links:

(Images: Via L2 and NASA. Special photography provided by Brian Papke, MaxQ/ (Lead image, and MPS photos), plus Philip Sloss (Ms Stilson photo). Many thousands of super hi-res image stock available on L2’s new Photo Section – around 750 gbs in size.

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