DM-3 Test:

The DM-3 motor was the third in a series of development motors to be tested and the most heavily instrumented solid rocket motor in NASA history, with a total of 37 test objectives measured through more than 970 instruments.

The previous test – DM-2 – was carried out with a total of 53 design objectives, measured through more than 760 instruments.

For that test, the motor was cooled to 40 degrees F – a ‘cold motor’ test – in order to measure solid rocket motor performance at low temperature, as well as to verify design requirements of new materials in the motor joints.

The DM-3 incorporated several performance-based improvements to the designs of the first two development motors. Additionally, the core of DM-3 was heated to 90 degrees Fahrenheit for this full-duration firing to verify the motor’s performance at high temperatures.

ATK have noted that initial test data indicates the motor performed as designed, producing approximately 3.6 million pounds of thrust, or 22 million horsepower, and burning for just over two minutes.

“This test is the third in a critical series of static tests to evolve and confirm the motor configuration while providing applicable technology maturation for next-generation systems,” noted Charlie Precourt, vice president and general manager, ATK Aerospace Systems, Space Launch Systems.

“This milestone is another step towards completing our Critical Design Technical Interchange activity this fall.”

With this test, NASA and ATK can specifically assess performance at the highest end of the motor’s accepted temperature range. Through development testing, the solid rocket motor will be certified to fly at ambient temperatures ranging from 40 to 90 degrees Fahrenheit.

A major test objectives from the firing related to verifying the performance of new materials in the motor joints at hot temperatures. Intentional flaws were introduced in the joint to allow hot gas to penetrate into part of the robust joint to verify joint performance.

“The data from these tests, along with information we have collected over the past three decades, confirms this is the most powerful solid rocket motor ever designed,” said Precourt.

“This performance makes the five-segment a great solution for heavy lift launch vehicles.”

For SLS/HLV Articles, click here: http://www.nasaspaceflight.com/tag/hlv/

DM-3 is the largest human-rated solid rocket motor in the world, measuring 12 feet in diameter and 154 feet in length. The five-segment motor is based on the Space Shuttle’s four-segment boosters, but it has been upgraded to incorporate modern technologies and materials that were not used on the shuttle booster. 

As a result it produces 30 percent more power than the four-segment motor while utilizing new materials that provide cost and weight savings.

Five Seg Roles:

Two vehicles may use the booster, after it was initially designed for use with the since-cancelled Ares I – as the first stage, and Ares V launch vehicle – which would have used two of the larger Solid Rocket Boosters (SRBs).

One vehicle ATK have angled the motor towards is an Ares I-type commercial vehicle known as Liberty, which was first proposed as part of NASA’s Commercial Crew Development-2 (CCDev-2) procurement.

Despite losing out on the CCDev down-selection, ATK appear to be continuing work with European aerospace group EADS unit Astrium, who would provide the liquid-fueled cryogenic core of the Ariane 5 vehicle, powered by the Vulcain2 engine, as the Upper Stage.

The most likely role for the five segment booster will be with the Space Launch System (SLS), which is a Shuttle Derived (SD) Heavy Lift Launch Vehicle (HLV).

With L2 documentation showing the final version of the 90 day report – which has been delayed numerous times since the start of the year – heading to the OMB on September 19, prior to heading to Congress on October 3, full details about the vehicle’s cost and schedule should be made public soon.

Costing documentation – cited as the source of recent “dramatic” reports, such as seen in the Wall Street Journal (citing an August 19 document) – have now been acquired by this site (L2) and will be fully overviewed in an upcoming article.

As far as ATK’s role in SLS, documentation (L2) shows the Utah-based company have proposed a Firm Fixed Price (FFP) contract for 10 boosters, available between 2012-2015, whilst noting available assets that can support up to 11 SLS missions prior to asset depletion in 2020.

ATK are proposing the initial use of boosters in their expendable mode, thus eliminating several hundred million dollars worth of recovery and refurbishment costs.

As it stands, SLS would debut with the five segment boosters, prior to a trade study to evaluate if a switch to a liquid booster would be the best route forward, as SLS begins to ramp up towards its fully evolved configuration.

Such a switch – according to preliminary schedules – would be implemented by SLS-5, although such a decision could be made later in the schedule.

For the fully evolved 130mt SLS vehicle, source notes claim a future static DM test could be provided by ATK as a pathfinder test for an upgraded booster, which would be in competition with the liquid counterpart.

Such an upgraded booster may include recently proposed change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” thus allowing higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi.

As previously reported, there are also proposals to use lighter weight nozzles with expansion ratios up to 12:1, although such a large scale change would require study at least at a Ground Support Equipment (GSE) level, given its relation to Launch Platform design.

Currently, documentation shows SLS is being associated with the unemployed Ares Mobile Launcher (ML), while upgrades to the existing Crawler Transporters – along with lifetime extensions – are being evaluated at the Kennedy Space Center (KSC).

Another SLS article will follow on progression towards approving the use of the orbiter Main Propulsion System (MPS) hardware – donated by the shuttle fleet - in the opening SLS vehicles, following a positive review at the latest Program Requirements Control Board (PRCB) meeting.

(Images: Via ATK Webcast and 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 no where else on the internet).

(L2 is – as it has been for the past several years – providing full exclusive future vehicle coverage, available no where else on the internet. To join L2, click here: http://www.nasaspaceflight.com/l2/)

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The Ongoing SLS Delay:

As admitted by NASA Administrator Charlie Bolden, the decision on the configuration of the Space Launch System (SLS) was made on June 15, a decision based on the winning Design Reference Vehicle (DRM) out of the Marshall Space Flight Center (MSFC) hosted RAC (Requirements Analysis Cycle) study effort.

Memos on the decision, based around the utilization of a Shuttle Derived (SD) Heavy Lift Launch Vehicle (HLV) – as requested in the Authorization Act – soon circulated at the main NASA centers, with references to an official announcement to be made on July 8, the launch date for STS-135.

In a sign of how widespread the information was, Atlantis’ commander Chris Ferguson told the media to expect the announcement on the next vehicle to be made on launch day, following his arrival at the Shuttle Landing Facility (SLF) from Houston. His statement wasn’t retracted, nor was it corrected, by NASA Public Affairs.

July 8 came and went, as Atlantis launched on the final NASA shuttle mission – and most likely the last domestic manned mission for several years.

General Bolden was then called in front of a “Full Committee Hearing – A Review of NASA’s Space Launch System“, where lawmakers were given the chance to ask questions about the delay in pressing on with the SLS.

After a tough opening question, the General gave arguably his most impressive public performance to date, holding firm on why he was not able to reveal specifics on the vehicle’s configuration. His defence was related to industry restrictions and an ongoing independent cost analysis effort by Booz Allen.

That costing effort – which began on July 5 – is likely to be completed by mid-August, while an announcement on the configuration of the vehicle, is expected “soon”.

 An attempt to request NASA push on with making a public statement on the SLS configuration to the media – to coincide with Atlantis’ landing at the Kennedy Space Center – was turned down by NASA’s leadership.

The continued delays to the announcement are now causing numerous managers and workers – at least those remaining after the massive jobs losses shortly after Atlantis’ return – to question if the delay is based on politically-aligned tactics to kill the SLS.

As many are aware, a second round of job cuts are expected to be carried out soon at key SLS bases – such as the Michoud Assembly Facility (MAF) in New Orleans, where managers have attempted to delay and extend WARN notices in the hope of bridging the gap between Shuttle and SLS – again based on the raised hopes of the June configuration decision by General Bolden.

The continued delays have now resulted in MAF’s management losing patience, as August 26 was set as the date for all of the remaining workforce – a key SLS skill set – to be released.

In effect, those opposed to SLS – such as the architects of the FY2011 plan – only need to delay another month before they can cite the “difficulties and costs” of having to rehire workers to build a vehicle which could have been announced when the workforce was still in place.

SLS Configuration and Schedule:

The SLS configuration is – as expected -  based around a SD HLV, using “Shuttle” boosters, engines and external tank heritage. However, information – acquired in the new L2 SLS section – has provided the most recent and comprehensive overview on the specifics of what is a core vehicle from the onset.

Click here for recent SLS Articles:
http://www.nasaspaceflight.com/tag/hlv/

Initially, the call was to debut the SLS in 2016. As recently noted, the schedule for the opening flight has moved to December 2017 – although it now has an actual mission.

The mission will be lunar, with SLS-1 lofting Orion (MPCV) on an unmanned mission around the Moon.

Ironically, SpaceX recently noted – during their Falcon Heavy announcement – they are close to such a mission capability, far sooner than 2017.

SLS-1 will debut the vehicle in a 2.5 configuration, utilizing three Space Shuttle Main Engines (SSMEs) – otherwise known as RS-25Ds, donated by the Shuttle fleet – on an 8.4m diameter “External Tank” core, stretching 212 feet in length, with five segment Solid Rocket Boosters (SRBs).

It will also sport a 5m “kick stage” – which sources claim is a man rated version of the Boeing Delta IV upper stage. This stage was also listed as one of the candidates for the Sidemount SD HLV.

Nearly four years will pass before the next SLS launch in August 2021, known as SLS-2, a vehicle which is identical to SLS-1, with the only difference being an element of the mission, which would be a manned trip around the moon in the MPCV, prior to a west coast landing in the Pacific.

Although the manifest is very much “to be decided” – August, 2022 would be the next launch date, with SLS-3 again using the same configuration, as would SLS-4 one year later.

SLS-5, in August 2024, would be the debut of the Cargo SLS, with a new fairing and a vehicle hardware change possible – as the winner of the booster competition would debut with this HLV.

While ATK’s Reusable Solid Rocket Motor (RSRM) boosters may continue, should they win the competition, sources claim a likely switch to an RP-1/LOX booster – although an actual engine for such a booster has not been cited at this time.

Sources note the potential options for the liquid booster engine range from a TR-107, to a cluster of AJ-26-500s, to maybe even SpaceX’s Merlin 2. Based on such a manifest becoming a reality, such options would have well over a decade to provide such an option for the SLS.

SLS-6 – August 2025 – would return to the manned configuration, although no mission other than “exploration” – possibly as part of a Near Earth Object (NEO) mission – has been cited by the information.

SLS-7 – August 2026 – a Cargo SLS launch, would see one change to the vehicle, as the expendable SSME – known as the RS-25E – would be employed on the vehicle, taken over from the exhausted Shuttle SSME stock. Again, three engines would be required, as much as all of the SLS vehicles will be designed to have “space” for five engines.

With the manned and cargo SLS’ taking it in turns for the single mission per year role, SLS-11 – August, 2030 – would be the next change, as the five engine core is filled with the two extra RS-25Es, utilizing the full core power plant.

This configuration’s debut would be a cargo based mission, followed by a crewed mission one year later.

And then, in August of 2032, the evolved SLS is expected to debut (see image left), again based on the same 5xRS-25E driven core, but this time with a full Upper Stage, becoming the 130mt+ HLV. This debut (SLS-13) would be – as expected – based around a cargo mission.

Sources note the Upper Stage for the evolved SLS would utilize three J-2Xs, an engine which was originally set be involved with the since-cancelled Ares vehicles.

Other notes of interest claim the Ares Mobile Launcher (ML) has earned a reprieve, after it was initially claimed it would be cheaper to build a new launch platform, as opposed to carrying out expensive changes to the Fixed Service Structure (FSS) and Launch Mount – both of which were very specifically designed with the Ares I in mind.

The Ares ML – currently parked near the Vehicle Assembly Building (VAB) – was also going to be hooked up to the Roller Coaster Emergency Egress System (ESS), a massive structure which was to be built in-situ at Pad 39B. However, it is understood that despite a large amount of money being spent on the design phase, this concept has been scrapped and won’t return for the SLS.

Other efforts, such as the modifications and long-term life extension of at least one of the Crawler Transporters (CTs) to provide the ride for the SLS to the pad, are continuing.

As noted at the start of the article, sources have noted this schedule is preliminary, based on a poor funding forecast – a “worst case scenario” manifest, although no one was able to provide even a draft version of an improved schedule.

(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.

(L2 is – as it has been for the past several years – providing full exclusive future vehicle coverage, available no where else on the internet. To join L2, click here: http://www.nasaspaceflight.com/l2/)

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 Solid Rocket Boosters:

As expected based on an excellent flight history, the Solid Rocket Booster (SRB) systems on STS-134/Endeavour performed extremely well during the May 16, 2011 launch. Only five items of interest of were noted on the booster systems during the standard In-Flight Anomaly (IFA) baseline report to the Space Shuttle Program.

In fact, only two of the five reportable squawks on the SRBs were worthy of IFA status: a Right Hand (RH) SRB main parachute failure and a separation debris event recorded by one of the RH engineering cameras on the SRB itself.

For the parachute failure, the SRB IFA presentation notes that a “Parachute tear was observed during diving operations. DAS video verified failure.”

The parachute failure, identified as a tear in the main chute, did not affect ascent performance of the SRB systems and has been classed in the Criticality 3 category.

Moreover, the loss of only one chute still ensured the safe splashdown and recovery of the SRB. Nonetheless, an SRB IFA was declared and an Anomaly Resolution Team (ART) formed to investigate the failure.

To date, the ART has reviewed DAS accelerometer data, which indicates that the “second disreef occurred earlier than experience although within requirements.”

Further post-flight inspections revealed damage at “gore #26″ on the parachute, damage that extended through the length of the chute.

An initial fault tree has been developed and a detailed inspection and photographic work-up of the damage hardware and pre-flight processing images is underway.

While investigators will make every effort to find root cause for this problem and ensure that it does not exist on STS-135′s SRBs, it is highly unlikely that this issue would cause any kind of delay to the STS-135 mission given that flight’s status as the final Program Flight.

However, the second IFA declared for STS-134′s SRBs is of a more serious nature, though significant progress is being made and is not expected to be an issue for STS-135′s launch on July 8.

This IFA was declared to document the liberation of a single piece of debris at MET (Mission Elapsed Time) 125.242 seconds near the RH SRB forward attach point to the External Tank (ET) during SRB separation.

“Debris appeared metallic and cylindrical. SRB Anomaly Resolution Team formed,” notes the SRB IFA review presentation – available for download on L2.

The ART quickly identified all potential sources for the debris from the forward assembly and compiled supporting and refuting data for each item to expedite the review and identification process.

This refuting and supporting data was compiled in part based on post-flight inspections of the SRB structure and systems.

From this compiled list of candidates, two gained mention in the SRB IFA review, with the first being a Ground Strap Coupler which was found to be missing during post-flight inspections.

The Ground Strap Coupler is used as a connection between the returned and non-returned ground straps between the SRBs and the ET.

The second though less-likely source for the debris is the Separation Bolt Lock Pin which is used to stake an insert on the ET-side of the hardware.

Since the ET-side of the hardware burns up in Earth’s atmosphere follow Orbiter/ET separation, it cannot be confirmed whether or not this component was still attached to the ET hardware following SRB separation.

Reusable Solid Rocket Motors:

As with the SRBs, Endeavour’s RSRM components performed splendidly during both of Endeavour’s 43-hour launch countdowns, with the IFA report from ATK – the parent company of the RSRMs – indicating that “All RSRM countdown parameters were within LCC/OMRS limits and within family.”

Likewise, ATK’s IFA presentation to the Space Shuttle Program (SSP) revealed that the performance of both STS-134 motors and their associated Booster Separation Motors (BSMs) was excellent and “well within CEI requirements.”

At the time of the IFA review on June 17, RSRM post-flight hardware evaluations were ongoing at the Kennedy Space Center, as were BSM inspections.

In Utah, at the production facility of the RSRMs, nozzle disassembly began June 16.

To date, no (ZERO) IFAs on the RSRMs have been declared and only eight squawks have been identified for further evaluation. Of the eight squawks, only six gained specific notes from ATK as part of their thorough IFA presentation to the SSP.

The first such squawk related to “sooted foam loss” from the Right Hand (RH) motor’s center stiffener ring. 

As noted in ATK’s IFA presentation, “An area of foam loss was noted at approx 300-degrees on the RH center stiffener ring. Exposed surface was heavily sooted.”

The resulting exposed area was elliptical in shape and carried dimensions of ~6inches x 3inches.  An engineering estimate on the mass of the missing stiffener foam registered at 0.2  lbs – with a conservative risk assessment prediction of 0.218 lbs.

Analysis of the area indicates that the foam loss occurred AFTER the rocket motors had separated from the STS-134 stack. This was confirmed via RH RSRM photos showing “a porta-pull location (on-motor pull test for foam process verification) on the RH motor. Sooted area in the photo is exposed during the foam pull testing and sees full ascent, plume impingement and reentry heating.

“Right hand photo shows Foam missing surrounding the sooted area was due to splashdown as shown by the lack of any stain or darkening.”

These photos were then compared to photos of the LH RSRM which displayed pieces of thermal curtain embedded in the stiffener foam. “Foam loss to bare case is lightly sooted showing this to be a reentry event with exposure to less than the full reentry heating,” notes the IFA presentation.

Click here for specific SRM/RSRM Articles: http://www.nasaspaceflight.com/tag/srb/

Here, the LH impact confirmed previous held beliefs that thermal curtain impacts on the RSRM stiffener foam can cause “bare case” exposure to the RSRM during the reentry environment.

“Comparison of the lab analysis of the residues in the three sooted areas and earlier test results showed that the RH foam loss occurred early in reentry heating.”

Therefore, there are no concerns with materials or foam processing and this squawk is not a risk to STS-135/Atlantis’s ascent next month as the foam loss does not violate previous flight rationale.

The second squawk mentioned in the IFA report was due to an unknown material on the RH Nozzle-to-Case Barrier O-ring.

The presentation notes that an “Unknown material (white/clear) was found on the surface of the barrier O-ring.”

Initial lab results indicate that the material is an adhesive from Teflon tape that is used in the area during nozzle installation.

“Material is suspected to have been moved over O-ring footprint during disassembly as no indent was noted on O-ring,” added the presentation.

This is not a constraint to STS-135 since the material is “gel-like and compliant and would not indict nozzle-to-case joint leak check even if was on footprint.”

The third squawk was a grease blockage of a leak check groove in the LH Igniter Outer Gasket. “Excessive grease was observed in the STS-134 (RSRM-113) leak check transmission groove at approximately 135 degrees,” notes the STS-134 RSRM review presentation.

The grease is usually located in the void region of the gasket sealing element and can be removed from the groove region by Mylar film.

The problem here is that excessive grease could “extrude from the void area during final bolt torque and although undesirable, excessive grease migration into the groove after leak check does not affect sealing or leak check validity.”

Since the igniter outer joint leak test is performed at a low bolt torque of 20 – 25 ft-lb, excess grease will not extrude from the void region until torque values are higher than 150 ft-lb. Therefore, there is no way for the grease to block the leak check groove at the leak test torque level, and there is no concern for STS-135.

The fourth squawk pertained to missing material on the LH and RH outer gasket primary seal cushion.  As noted by the IFA presentation, “Damage was observed on the forward face seal cushion of the STS-134 (RSRM-113) outer gasket primary seal in-line with the leak check thru-hole.

“The gasket crown (not the cushion) is the sealing element for the gaskets and is deformed during installation to provide the seal.”

A similar issue was noted on a 5-segment Demonstration Motor (DM-1) in 2009.

Here, the flight concern revolves around whether or not rubber damage could compromise the gasket seal (crown) and potentially “challenge” other hardware functions.

Moreover, “Recent install tool change, in combination with inherent hardware tolerances, show increased propensity to result in leak check thru-hole partially over rubber in assembled condition.”

Therefore, rubber can extrude into the thru-hole at assembly and at motor pressurization, a dome movement could result in a shear-off of extruded rubber cushion.

However, there are “No credible scenarios for potential overlap to result in inadequate leak check, damage to crown, or misplaced rubber material to affect seal integrity.”

STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/

A review of all data on the RSRM-114 set on STS-135 revealed no potential overlaps with the crown.

The penultimate squawk listed on the STS-134 RSRM IFA review was taken to document a foreign hair-like material on threads of the LH aft vent port top plug and LH aft vent port closure plug.

The IFA noted that an impression on the O-ring surface was noted after the hair-like materials’ removal. The hair-like materials are currently being analyzed to determine precisely what they are.

“First squawk was written to document and  sample for lab analysis a foreign (hair like) material on threads of the LH aft vent port top plug. Second squawk was written to document and sample for lab analysis a foreign (hair like) material on LH aft vent port closure plug,” noted the IFA presentation. 

“An impression was also observed remaining in O-ring surface. At this point, the two fiber appear similar and are being analyzed to determine type and size.”

Finally, the last squawk on the STS-134 RSRMs was a retainer surface indication on the LH igniter outer gasket.

“Discontinuity noted on metal (retainer) surface of outer gasket on LH igniter.”

The gasket has been shipped to Utah for lab analysis.

(All images via L2 acquired presentations – STS-134 IFA Review for SRB and RSRM. Post STS-134 coverage of Endeavour is continuing in L2, which will follow Endeavour all the way to her retirement home in California).

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SLS Studies:

Months – if not years – of studies and reviews have surrounded the selection of NASA’s new Heavy Lift Launch Vehicle (HLV), only for the aforementioned studies to consistently provide a “winning configuration” known as the Shuttle Derived (SD) Heavy Lift Launch Vehicle (HLV).

While the very nature of a SD HLV being the “best choice” for NASA is a point of conjecture in numerous arenas, the studies never led to any firm decisions being taken at the NASA leadership, or more importantly at the political level.

With the President’s FY2011 budget proposal proving to be highly unpopular, the Senate’s Authorization Act changed NASA’s course and put its weight behind a Space Launch System (SLS) which utilized both Constellation (Ares) and Shuttle hardware.

This Act was based on consultations between lawmakers, space industry heads and NASA managers on the best approach for both supporting the International Space Station (ISS) in the second half of this decade, prior to evolving into the required HLV for Beyond Earth Orbit (BEO) missions.

However, the Act’s requirements appeared to be met by a level of disapproval from NASA leadership, as yet more studies were ordered, resulting in the Marshall Space Flight Center (MSFC) led review of potential launch vehicle configurations via three RAC (Requirements Analysis Cycle) teams.

Click here for NASASpaceflight.com HLV/SLS- related news articles: http://www.nasaspaceflight.com/tag/hlv/

As the RAC studies were continuing, a preliminary report into the SLS from NASA also highlighted budget and schedule concerns – much to the surprise of some RAC team members – although the report was embedded with caveats in finalizing their costings and evaluations on its own claims.

Internal Program-level Frustrations:

A final report to lawmakers is now well overdue, leading to frustrations surfacing from within NASA at even the management level. One of the more impassioned speeches came from Launch Director Mike Leinbach, who addressed his Firing Room workforce after the S0044 Launch Countdown Sim was completed.

Paraphrased highlights from the speech quickly became the subject of high praise from those who had worked the sim. However, a recording of what was actually said has since been acquired by this site, after the audio file spread throughout several NASA centers – again gaining nothing but praise for the highly respected manager - as it provided one of what is believed to be many examples of frustration from within NASA.

“For the final S0044 folks, what I’m about to say would not be appropriate on launch day, and this is our last chance to talk together,” noted Mr Leinbach over the recorded Launch Director loop (transcribed from an audio recording via L2).

“The end of the shuttle program is a tough thing to swallow and we’re all victims of poor policy out of Washington D.C., both at the NASA level and the executive branch of the government and it affects all of us – it affects most of you – severely.

“I’m embarrassed that we don’t have better guidance out of Washington DC. Throughout the history of the manned space flight program we’ve always had another program to transition into – from Mercury to Gemini, and to Apollo to the Apollo-Soyuz test program, to Skylab and then to the shuttle – we’ve always had something to transition into.

“And we had that, and it got cancelled and now we don’t have anything, and I’m embarrassed that we don’t. Frankly, as a senior NASA manager, I’d like to apologize to you all that we don’t have that – so there you are. I love you all, I wish you all the best.

“We will press on through this flow and this launch in the way we always do. We’re going to play this game to the final out and then we’ll be done. I just wish you all the best, and again Godspeed to you all. Thank you.”

As the loop was opened, rapturous applause could be heard ringing around the Firing Room.

SLS Decision:

However, a follow-on vehicle is close to being officially announced, following an increased amount of activity at the executive level this week, resulting in a top level meeting between the SLS leadership and NASA administrator Charlie Bolden, which finally picked the configuration.

“SLS and GO briefed Bolden on a proposed SLS architecture with the following decisions made (finally),” noted one memo (L2). “8.4m core and Upper stage. RS-25s (Space Shuttle Main Engines) on core stage. J-2X on Upper Stage. 4 or 5 segment solid boosters for initial flights.”

While the boosters are highly likely to be five segment motors, the “initially” reference was explained, noting the evolved BEO SLS is yet to know if it will ride with SRBs or Liquid boosters.

“Competed boosters for evolved vehicle (between solid boosters and LOX/RP-1 (Kerolox) boosters),” added the memo. “RFP (Request For Proposals) to be quickly developed to provide data on competed boosters.”

However, ATK have been quick off the mark in informing NASA’s leadership they are ready to support, not just with the initial SLS, but also into the future, via the 130mt class vehicle.

According to source information, the Utah-based company – and home of the RSRM (Reusable Solid Rocket Motor) – have proposed a Firm Fixed Price (FFP) contract for 10 boosters, available between 2012-2015, whilst noting available assets that can support up to 11 SLS missions prior to asset depletion in 2020.

This is notable, given ATK are proposing the initial use of boosters in their expendable mode, thus eliminating several hundred million dollars worth of recovery and refurbishment costs. Sources also add that ATK’s approach from a “cost and schedule” standpoint has been highly impressive.

As far as ATK’s approach for the fully evolved SLS vehicle, source notes claim a future static test could be provided as a pathfinder test for an upgraded booster.

Such an upgraded booster may include recently proposed change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” thus allowing higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi.

As previously reported, there are also proposals to use lighter weight nozzles with expansion ratios up to 12:1, although such a large scale change would require study at least at a Ground Support Equipment (GSE) level, given its relation to Launch Platform design.

KSC information has also noted that preliminary assessments will be used to find a use for the Ares I Mobile Launcher (ML), currently sat near the Vehicle Assembly Building (VAB) with no future role to play, following the cancellation of the Constellation Program (CxP) and thus its main customer, the Ares I.

Presentations on the 21st Century Launch Complex proposals (L2) – a stunning set of documents which include the “Point Of Departure” Architecture overviews (and will be the focus of upcoming articles) – also mirror the comments which point to the SLS joining forces with the Ares ML, as much evaluations are continuing into a need for the ML to play a role until the evolved SLS.

“Allocate ML for SLS. Modifications to support SLS architectures, with scarring for extensibility. Incorporate standardized interfaces, using mobile launcher to adapt to  vehicle requirement,” noted the Architectures Refinement Cycle 5.0 section of the latest presentation (in June) via L2.

It is also understood that Boeing will be the main contractor for the SLS vehicle, likely explaining their work at the Michoud Assembly Facility (MAF) on a small scale strongback core, as much as it is likely the first SLS test flight will utilize the stored Light Weight Tank (LWT) ET-94.

The role of Pratt & Whitney Rocketdyne (PWR) appears to be secure for at least the opening gambit of the SLS growth towards its 2016 IOC (Initial Operating Capability), with 12 RS-25Ds available for one-off roles with SLS flights, following their transition from the Space Shuttle Program (SSP).

It is not yet known if a transition to the expendable RS-25E will be made after the four sets of RS-25Ds have been used.

After being the long lead item for Ares I, the Upper Stage J-2X is continuing to make progress, after recently becoming housed in the A-2 Test Stand at the Stennis Space Center (SSC). Beginning in mid-June, the engine will undergo a series of 10 test firings that will last several months.

“An upper stage engine is essential to making space exploration outside low-Earth orbit a reality,” said Mike Kynard, manager of the J-2X upper stage engine project at NASA’s MSFC in a recent public statement.

“The J-2X goes beyond the limits of its historic predecessor and achieves higher thrust, performance, and reliability than the J2. We are thrilled to have the engine in the test stand to validate our assumptions about engine performance and reliability.”

It’s role with the SLS was one of the initial key requirements ordered by General Bolden, after he rejected the two-phase SLS approach.

(The progress on the SLS status will continue to be followed up over the coming weeks. L2 members, follow our exclusive SLS update coverage via the SLS and HLV tags. Images used:  Via L2 content and NASA.gov – plus Mr Leinbach photo via Brian Papke, MaxQ Entertainment/NASASpaceflight.com).

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The HLV Centrepiece:

The process to finalize the new path for NASA – following the cancellation of the Constellation Program (CxP) – remains under evaluation. The lack of a clear direction continues to burden the Agency, something which will continue to be the case even after the centerpiece rocket is revealed.

Although the ultimate goal for the Agency’s exploration plan is manned missions to Mars, no definitive roadmap has risen from the ashes of the Ares-based architecture, resulting in a path where a Heavy Lift vehicle is being designed before the missions it is set to cater for have been set in stone – something which often is pointed out as the wrong way around.

However, with the knowledge that very large payloads will need to be lofted uphill for the future goals, NASA teams are steadfast in their opinion that an HLV is required, a sentiment SpaceX – often championed as the exciting alternative and cheaper path for the United States to once again carry out manned BEO missions – agree with, as much as they embedded the caveat their agreement is specific to trips to Mars.

“Falcon Heavy should not be confused with the super heavy lift rocket program being debated by the U.S. Congress,” SpaceX officially cited when revealing their Falcon Heavy launch vehicle. “That vehicle is authorized to carry between 70-130 metric tons to orbit. SpaceX agrees with the need to develop a vehicle of that class as the best way to conduct a large number of human missions to Mars.”

Top level NASA meetings late last week (notes on L2′s SLS section) once again emphasized their agreement with the HLV requirement in the Authorization Act – which was based on NASA input during its drafting – noting that all findings concur there are no real savings in multiple smaller launches, which they claim also increase risk.

Such claims are often questioned, when citing alternatives such as EELVs and other commercial medium lift vehicles.

The main question for SLS at present relates to the configuration of the HLV, with the bulk of the RAC (Requirements Analysis Cycle) studies now concluded at the Marshall Space Flight Center (MSFC).

SLS Approach (all notes via L2′s SLS Section):

As previously reported by this site – and later by other media – a plan was created to fly a Block 0 SD (Shuttle Derived) HLV for four flights, starting in 2016, prior to an open competition to study the options for the evolved SLS which will carry out the BEO missions.

This approach was sent to NASA HQ late in May, only for it to be rejected by NASA administrator Charlie Bolden, who returned the plan to Marshall, tasking the teams to draw up baseline 70 MT vehicle which must fly by 2016 and must be able to evolve to 130 MT.

The order also noted the vehicle must be powered by LH2 (Liquid Hydrogen), powered by RS-25s (SSMEs) or RS-68s, while the Upper Stage must work under the assumption of using the J-2X hardware. However, the teams were allowed to trade on the boosters, between Solids and Liquids. Marshall were asked to send back their findings by June 1.

The result of what was sent back to NASA HQ was revealing, with high level meetings late this week noting the approach is now working with the clear requirement for a “staged evolution of a single large vehicle” – evolved to 130 MT. In other words, the initial 70 MT SLS will be the baseline/template for the 130 MT version.

This vehicle, which continues to be tagged as the Design Reference Vehicle (DRV) for the purpose of the final report to lawmakers, will enable use of core elements, “initially” – the notes claim – utilizing Solid Rocket Boosters to allow the SLS to provide back-up in the 2016-early 2017 time-frame for the ISS support assurance – as requested in the Authorization Act.

As such, the SD HLV RAC-1 option is still leading as the Design Reference Vehicle and is now undergoing a refinement on two areas, the core structure and the core engines, resulting in what would be more fairly described as a hybrid SD HLV, one which will grow within its own skin to evolve into a 130MT vehicle.

The meetings also noted the often-favored Kerolox (RP-1) option is not classed as a viable option, although it was claimed the RAC-2 option proved to be a worthy opponent of the SD HLV, by causing the re-examination of many of the key issues which challenged the leading DRV option.

The biggest challenge noted is the structuring of the procurement approach, along with the program management/oversight path, cited as where they expect to achieve the maximum savings, cost and sustainability, to a point NASA expect SLS to be “viable” under the rules of the Authorization Act – a key change to the preliminary report presented by NASA to lawmakers.

A definitive design and basic systems decision is expected before the end of June, even though these findings may lack the procurement and management strategy at that point. There is understood to be a hard deadline of July 8 – when Atlantis is scheduled to launch on the final Shuttle mission, STS-135.

SLS Hardware – SRBs:

With the allowances to examine Solid versus Liquid boosters on the SLS, the latest meetings would only commit to Solids being used “initially”, as much as sources expect they will win out as the long term solution for the evolved SLS.

A “non official” proposal of using liquid boosters on the HLV was created by a NSF forum member Nate Downes, which cites the liquid option as advantageous due to the simplicity of handling, superior impulse and the logistical advantages of pad fueling simplicity, which enables a wider range of missions for the same cost.

ATK appear to be fully aware their long-term role in SLS is not set in stone and have been busy providing costings and options to both the Marshall teams and “people in power” in Washington, DC.

While information on the latter is unlikely to see the light of day, L2′s SLS section acquired information on one example of a proposal to “boost” the capability of the SRBs over time, evolving the noisy duo which would aid the vehicle’s first stage flight, in tandem with the SLS’ evolution.

This example, provided to the RAC Team 1 at Marshall, proposes the change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” to allow higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi.

There are also proposals to use lighter weight nozzles with expansion ratios up to 12:1, although such a large scale change would require study at least at a Ground Support Equipment (GSE) level, given its relation to Launch Platform design.

Such challenges can be seen in a similar – yet not entirely related – change which was proposed for boosting Ares I’s capability three years ago.

“Extended Nozzle – Ares First Stage: Increase Ares I nozzle expansion ratio from 7.2 to 9.3,” noted a Constellation presentation acquired by L2 in 2008. “Justification: Provide 1200-1300 lb increase in overall vehicle payload capability.

According to that presentation, a larger 10.25 expansion ratio was preferred as “optimum” – though impacts to shipping, manufacturing, the TVC (Thrust Vector Control) hardware and the Mobile Launcher had to be considered in the approved ratio change.

“9.3 expansion ratio provides optimum performance with TVC attach constraints and manufacturing limitations,” cited the document.

ATK are continuing to make preparations for the DM-3 test of their five segment booster at their test facility in Utah.

SLS Hardware – Core Engines:

As has been proposed for some time now, the opening flights of the SLS are highly likely to utilize the existing four sets of Space Shuttle Main Engines (SSMEs) from the Shuttle Program – consisting of three sets from the last three flights of the shuttle and one spare set, all located at the Kennedy Space Center (KSC).

Click here for NASASpaceflight.com HLV/SLS- related news articles: http://www.nasaspaceflight.com/tag/hlv/

These RS-25Ds were also the centerpoint of the Block 0 SLS under the now-cancelled two-phased approach, which was to fly four times in support of the International Space Station and for opening Orion (MPCV) flights.

The current plan would result in a transition to RS-25Es, a cheaper and expendable version of the SSME, for the next evolution of the SLS.

As noted in a Program Requirements Control Board (PRCB) presentation last year, Pratt & Whitney Rocketdyne (PWR) were placed under an order to “delay the disposal and retain the capability” to manufacture new SSME-based engines.

“SSME New Production Strategic Capabilities (SCA) supports the manufacture of all current configuration major Block II engine components. New production line items consist of manufacturing tooling / equipment, raw materials, hardware details and sub-assemblies,” noted the PRCB presentation.

“Previously approved for retirement at NASA boards (2007/2008) – (overturned). Supports future launch vehicle architecture pending Agency decision.”

Although this is the leading option, the top-level meetings late last week confirmed some trades are continuing on the core structure and core engines, in order to ensure the best configuration for the “staged evolution of a single heavy launcher”.

SLS Hardware – Core Structure/Tank:

The core of the SLS first stage is where a large amount of refinement is taking place.

Firstly, the remaining ET specific workforce at the Michoud Assembly Facility (MAF), who – from managers and engineers – have spent most of their “remaining days” clearing out work stands and equipment from the 420 building to make room for the filming of a Hollywood movie, were expecting to get their 60 day WARN notices on May 26.

Lockheed Martin management informed these workers this was no longer the case, and will instead continue under a temporary funding request, due to what they cite as changes for the end date/funding for the ET program through to the start of a SLS program, which they project will be known this month.

Over at the Boeing side of MAF, managers have hired back previously released ET welders – badging them to Boeing from Lockheed – for the fabrication of what is known as the Pathfinder Tank – a scaled “strong back” tank.

Tooling is already in place to start this work and hardware is being moved into position.

Officially this is not an HLV/SLS project because this is being run as an “unsolicited” Boeing project, with a view for it to become part of the SLS program. However, the work is known to relate to the structural strength of the ET core on the first stage when stretched to a taller SLS configuration, along with modifications to the LH2 tank to support the SLS engine package.

This work on the Pathfinder Tank is being staged in the RWT (Robotic Weld Tool) area. The tooling/form/jig to hold the components together for the weld is being set up, as training for the operators is conducted ahead of the actual prototype being fabricated.

The key information about the Pathfinder relates to the domes being worked, which are classed as spun aluminum – single piece dome – versus the paneled dome used to produce the Shuttle ET.

Eventually, the fabrication will lead to a small scale LH2 tank, using the single piece (spun) dome, which will be used to show it is able to cope with SLS’ load requirements.

The Lockheed MAF planning group have also been told to start writing procedures to bring the MAF VAB (Vehicle Assembly Building) back on line in the event of starting production again – showing a major move to a running start at the time of a SLS decision point.

Currently, the LWT ET-94 remains vertical in the MAF VAB. ET-139 is in situ after the Stringer investigation work, while parts for ET-140 and ET-141 remain in storage.

MAF source information notes they have enough material for two new tanks already on site, but they will have to start up the smelter if they want to make more components.

SLS – KSC:

With the painful job losses continuing to be suffered at the Florida Spaceport, Director Bob Cabana addressed his workforce last week, announcing a Center Director forum in the summer, as he aims to transition the center into the focal point for hosting government and commercial launch service providers.

Mr. Cabana also noted that NASA’s future architecture is emerging, and that he expects a decision “this summer” on the configuration of the SLS, citing KSC has a lot of important work over the coming months and years.

Ironically, KSC has already made a decision relating to hosting a HLV at the spaceport, after the entire Crawler Transporter group – which was already under layoff notice – was told they are keeping their jobs via KSC allocating funding for them to work man hour/material/project estimates for upgrading the famous Crawlers for SLS.

The group was told that NASA Ames had finished design on new Jacking, Equalization and Leveling System Cylinders (16/CT) and bearings, as well as work on new Rollers (88/CT, over 2000lbs/roller, heavy duty, mombo rollers and bearings/bushings) for the belts/shoes.

New GenSets for more AC Power to support the increased demands are in the pipeline too. These upgrade modifications will begin in about four to six month’s time.

Initial testing was completed last year on one area of crawlerway just outside of Pad 39B, via a strange looking contraption which aimed to test the impact of over 25 million pounds on the rock surface of the track.

The findings of the testing, which was conducted by NASA, the United Space Alliance (USA), Architect and Engineering firm Jones Edmunds and Associates (JEA) and a couple of additional contractors, was classed as positive.

No references have been made into the use of the Ares I Mobile Launcher (ML), which remains sat next to the VAB, with a launch mount which is highly specific to the Ares I vehicle.

All This Has Happened Before – Will It Happen Again?:

The saga revolving around NASA’s next Heavy Lift Launch Vehicle has been ongoing for years. Winning trade studies and being a leading option does not provide any certainty such a vehicle will ever see “hammers on aluminum”, as seen just prior to the FY2011 Budget Proposal announcement.

In the weeks leading up to the FY2011 announcement, General Bolden himself tasked a special team to conduct a study into the HLV options, which resulted in the Sidemount HLV and RP-1 (Kerolox) vehicles losing out to the in-line SD HLV.

“HLV study summary from (Mr. Jeff) Hanley – Sidemount doesn’t buy anything and takes hit on safety. A couple of (winning) versions of In-line going to (Mr.) Bolden,” noted one memo surrounding the study at the time. MAF also noted they were all set to implement the plan.

However, the end result was a complete omission from the FY2011 announcement, which focused on a five year study into “game-changing” propulsion, effectively mothballing the HLV bar a small team, before the lawmakers reversed the decision via their Authorization Act.

The coming weeks will prove to be critical for this latest approach to providing NASA with the blueprints for a new HLV.

(The progress on the SLS status will continue to be followed up over the coming weeks. L2 members, follow our exclusive SLS update coverage via the SLS and HLV tags. Images used:  Via L2 content and NASA.gov).

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STS-133 Processing Latest:

Discovery is now back into a nominal pad flow, thanks to the excellent work by engineers and technicians who successfully worked through the weekend to clear the Interim Problem Report (IPR-47) relating to requirement to changeout two internal seals on the right OMS crossfeed flange plumbing.

*Click here for NASASpaceflight.com articles on IPR-47: http://www.nasaspaceflight.com/tag/ipr-47/

The work was conducted ahead of schedule, thanks to the sooner-than-expected eduction of the system after the fuel was offloaded, with acceptable Toxic Vapor Check (TVC) sample readings recorded a full day ahead of schedule. 

With no issues relating to the changeout of the seals, good mass spec leak checks and the timely reloading of fuel into the OMS tanks, the issue was officially cleared as a constraint early on Monday.

“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (Pad-A): S0072 LH/RH OMS/RCS Fuel Offload was completed Friday morning. IPR-47 cross-feed flange leak: Cross-feed flange eduction was completed Saturday morning with acceptable TVC sample readings. Seal R&R was completed Saturday evening along with the cross-feed flange reassembly,” noted the NASA Test Director (NTD) report on Monday (L2).

“TVCs post-S0024 and prior to cross-feed line heater insulation re-installation were acceptable. The 59-64 ‘doghouse’ door is installed for flight. Carrier Panels are in work.  S0024 OMS/RCS (Reaction Control System) Hyper Fuel Load: OMS/RCS fuel load was completed on Sunday.

“Pad A was opened for controlled work at 22:00 EDT Sunday night. Aft Propulsion System (APS) quick disconnects have been removed and the flight caps installed.”

With the issue cleared – along with the successful resolution of a sensor which required a retest – Discovery can look forward to closeouts for flight, along with Monday night’s ordnance installation and connection tasks. Although most – if not all – of the remaining contingency days in the flow have been used up on IPR-47, Discovery is already closing in on S0007 Launch Countdown operations, set to begin on Friday.

“S1005 LOX Dewpoint/Conditioning was completed on Friday. PPO2 sensor cal/retest for IPR-0051 was completed on Friday,” added the NTD report. “S5009 Ordnance Installation/Connection is scheduled for tonight. S1287 orbiter aft closeouts and S0007 launch countdown preps continue.”

STS-133 Agency FRR:

The FRR was completed in just over half a day – shortly than a number of recent FRRs – a sign of a smooth review by the numerous presenting departments and managers.

STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/

“All orgs polled go to proceed toward launch on November 1st. Great job by Royce Renfrew and Bryan Lunney representing MOD’s excellent preparation. ISSP summarized consumables, ECLSS (Environmental Control and Life Support System) status and the status of some 24S (Soyuz) anomalies none of which have a constraint to STS-133/ULF5,” noted a post-FRR overview to managers (L2).

“SSP reviewed previous anomalies, configuration changes, and first flight items. The primary and secondary seals in the leaking crossfeed flange have been replaced. The crossfeed line pressure was increased and toxic vapor check performed with no further leakage detected. Shuttle processing is on schedule.”

Despite a “late breaking Orbiter item – Pyro shock numbers computed incorrectly. They looked at everything in the payload bay and all are okay so no issue,” the Agency FRR confirmed a “Go to proceed toward November 1st launch.”

As always, the Agency FRR is aided by a large amount of work that was conducted at numerous center and departmental FRRs over the past month or two, which led into the SSP FRR earlier this month.

At the SSP FRR, only one “action item” was noted, relating to the two boosters which will aid Discovery’s first stage ascent next Monday. Specifically, the FRR managers reviewed a test failure on a frangible nut – part of the SRB Hold Down Posts (HDPs) which release the vehicle during launch.

“Problem: Lot AAY Frangible Nut S/N 3000444 failed 110 percent web margin test during Destructive Lot Acceptance Testing (DLAT). 110 percent web thickness configuration with single crossover booster assembly. Failed to sever completely into two pieces (minimum) and release from test stud as required,” noted the SRB FRR presentation (all FRR presentations available on L2).

“Discussion: Observations noted after booster cartridge firing. Frangible nut stayed attached to test stud. Preload relieved during firing. Minimal force required to dislodge stud. Visual inspection after nut removal found one outer web intact. No thread anomalies noted during test stud inspection.

“Lot AAY frangible nut data pack review found no anomalies. Fabrication, inspection and testing met requirements. Nut material strongest produced to date.

Although such a failure during a launch would result in a LOV/C (Loss Of Vehicle/Crew) scenario, the action item gained the expected Flight Rationale in time for the Agency FRR at the Kennedy Space Center, given STS-133′s boosters are using nuts from a lot that has already passed its related testing.

“Flight Rationale: Frangible nut installed on STS-133/BI144 from Lot AAW successfully passed Lot Acceptance Testing (LAT) and flown since STS-125/BI137,” added FRR materials. “Failure isolated to Lot AAY. Booster cartridge installed on STS-133/BI144 from Lot AAU successfully passed qualification tests and LAT and flown since STS-126/BI136.”

“The SSP FRR action to review the frangible nut Destructive Lot Acceptance Testing (DLAT) was closed,” added the post-Agency FRR notes. “This nut came from Lot AAY, which is currently slated for STS-335. Lot AAW frangible nuts are installed on STS-133 and STS-134 so this anomaly has no impact to these flights.”

The FRR presentations also covered other items of interest, from the SRB recovery/disassembly operations, which are “ready to support pending completion of open work – includes repair of Hangar AF slip concrete apron,” and the minor In Flight Anomaly (IFA) items from STS-132.

“IFA STS-132-B-001 for the Forward Booster Separation Motor (BSM) exit cone closeout RTV-133 debond and liberation is no constraint to STS-133/ULF5,” noted the post-Agency FRR notes. “The RTV-133 seal is an environmental seal and not for thermal protection. Most likely cause considered water impact or retrieval based on lack of loads or environments to liberate during flight and drogue parachute suspension line entanglement likely contributor.”

The boosters will also be sporting a redesign to the SRB Thrust Vector Control (TVC) Auxiliary Power Unit (APU) fuel pump, which was initially set to debut with STS-134, prior to the manifest alignment which placed Endeavour’s flight behind STS-133.

The redesign, which was covered in depth via Program Requirement Control Board (PRCB) documentation (L2) and the resulting article on this site, will eliminate the highest – although extremely unlikely to occur – ‘critical 1′ failure scenario, which holds the potential of a LOV/C (Loss of Vehicle/Crew) event.

“Background: Current SRB fuel pump carbon seal prevents hydrazine leakage from fuel pump drive shaft to overboard drain line. Loss of carbon seal results in metal-to-metal contact (between rotating drive shaft and seal adapter) leading to fire or explosion, loss of APU with possible loss of mission under worst case conditions (Criticality 1). Represents highest SRB risk per current Shuttle Probability Risk Assessment (PRA),” noted the FRR materials.

“Discussion: Implemented Phase II fuel pump as alternate configuration. Redesigned pump based on Orbiter fuel pump design and eliminates carbon seal Criticality 1 failure scenario. No new failure modes introduced with Phase II fuel pump. Potential to eliminate one accepted risk hazard cause with full implementation.

“Currently no change in cause counts as alternate design. Full implementation planned for STS-134/BI145 and STS-335/BI146. Represents decrease in risk.”

In conclusion, the FRR – as would be expected – certified the use of the new pump, passing on the qualification reports and proven commonality with flown-hardware.

“Basis for Certification: Test, analysis and similarity. SRB APU Phase II Fuel Pump Qualification Report: All functional, vibration, shock, acceptance and five mission duty cycle tests successfully completed.

“Analysis shows affected components meet requirements for margins and safe-life as applicable. Similarity to current SRB and Orbiter fuel pumps used for qualification.”

(All images and graphics via L2).

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DM-2 Test:

Tuesday’s test related to the first stage of the Ares I launch vehicle – which remains NASA’s POR (Program Of Record) – although even ATK have recognized the on-going political refinements to NASA’s future, by associating the test of the booster as hardware that has been “identified as a key element of NASA’s future Heavy Lift Launch vehicle.”

Utilizing data from the opening five segment test – with DM-1 back in September of last year – a total of 53 design objectives will be measured through more than 760 instruments.

The motor was cooled to 40 degrees F – resulting in this firing being a DM-2 is a ‘cold motor’ test – in order to measure solid rocket motor performance at low temperature, as well as to verify design requirements of new materials in the motor joints.

“These new materials will allow for the elimination of joint heaters that were necessary in the original 4-segment motor design. This will save significant weight, further reduce system complexity and simplify launch operations, while simultaneously delivering increased operating margins at lower ambient temperatures,” noted ATK.

Other objectives include data gathering on vital motor upgrades, such as the new insulation and motor case liner and the redesigned nozzle which increase the robustness of the design. When fired, the motor produced a maximum thrust 3.6 million pounds, or 22 million horsepower.

“A robust ground and flight test program is a critical part of human-rating to ensure reliability and safety when launching crew into any orbit,” noted Charlie Precourt, VP and GM of ATK Space Launch Systems. “This test is a vital milestone in further growing the performance database for this new five-segment solid rocket motor.

“We designed this motor using a knowledge base gained from over three decades of operations, during which we constantly monitored and improved our design.”

The cases involved with DM-2 have all previously flown on with the space shuttle, collectively launching on 57 missions.

SD HLV Latest:

Following the rollout of President Obama’s FY2011 budget proposal, the role of the solids appeared to have a rather cloudy future, with a call for a “game-changing” HLV to result from a five year study.

While assessments and studies are commonplace for NASA – notably highlighted ahead of the FY2011 budget proposal, when a SD HLV appeared to have large levels of Agency support, prior to vanishing from the President’s vision – the political refinements to the future of NASA continue to focus on a HLV that will draw from the current shuttle technology base and skillsets.

A large 726 page assessment presentation (L2) was completed by the Space Shuttle Program (SSP), mainly focusing on the Sidemount SD HLV, prior to restarting to complete the Inline section of the documentation. However, the original purpose of the study was to finalize the assessments, for the benefit of passing on the knowledge to a potential suitor of a HLV.

Also see:
Part 1: Completed SD HLV assessment highlights low-cost post-shuttle solution
Part 2: SD HLV review outlines ISS Logistics and Transport
Part 3: Lunar/BEO – SD HLV, Commercial and International Architecture Outlined
Part 4: SD HLV: Early SPS Demo Mission Outlined – Risk Assessments Findings

With large support from the US Senate’s FY2011 refinements, the central role of a SD HLV has been returned to the forefront.

Signs of an Agency position, via a refined roadmap, is also showing signs of maturing, as a body known as the Human Exploration Framework Team (HEFT) work through evaluations into providing a viable path that reaches out as far as 2028.

“EA/Engineering: We briefed Charlie (Bolden) and Lori (Garver) on HEFT in mid July and they accepted our recommendations will talk to the Senate about those,” noted the latest Staff Senior Meeting notes (L2).

“The HEFT team talked to the steering council. The team will continue through August 31st and then turn it over to a long term HEFT team.”

Documentation on the HEFT effort was acquired by L2, which provided key overviews on their findings and recommendations – several articles to follow, covering interesting elements, such as the In-Space Exploration vehicle.

On the HLV, the HEFT noted the key role such a vehicle would have in the exploration architecture, while dismissing the need for a five year study

“Launch Vehicle Findings: An HLV is central to any robust human exploration program. Delaying a decision on HLV configuration and requirements to 2015 limits NASA’s options and hampers planning. There is no benefit to delaying work on the HLV, no technology needed for capability development,” noted the HEFT presentation (L2).

“NASA will lose an opportunity to build from the existing flight-proven systems. Losing the capability to build an SSP-derived HLV will require the development of new manufacturing, processing, and launch infrastructure at additional cost and schedule risk.

Three vehicles were assessed/outlined by HEFT, with a Saturn V heritage 33′ diameter RP-1 HLV, sporting 1.25 m lbf RP engines/boosters, 1.25 m lbf thrust class LOX/RP-1 core stage, and a J-2X-285 Upper Stage, was noted as problematic.

“An RP-based HLV (100-120 t) and a replacement for the (Russian) RD-180 is higher cost to NASA and therefore requires supplemental funding from DoD (Department of Defense) to offset increased costs,” noted the HEFT.

“RP-Based Vehicle Advantages: Vehicle architecture provides more capability and flexibility (114-157 t with and without boosters). Eliminates reliance on RD-180 Atlas V. Expands US liquid propulsion industry capabilities. Shared production infrastructure with the Air Force.”

The SD HLV equivalent was also listed, based on a 33′ diameter core, driven by RS-68Bs, evolvable to RS-68B E/O, and five segment PBAN boosters, evolvable to HTPB – with an Upper Stage powered by J-2X.

Yet it was the recommendation in HEFT’s conclusions to “Accelerate Shuttle-derived, in-line Medium Heavy Lift Implementation” that pointed to the configuration of choice, one which mirrors – but does not cite by name – the notional Jupiter-246 SD HLV.

“Shuttle-Derived Advantages: Lower DDT&E – fits within Agency budget for HSF (Human Space Flight) development. Schedule benefits – evolves current hardware (2-3 years faster). Utilizes experienced workforce. Based on hardware with demonstrated reliability and performance (101-118 t),” the HEFT noted.

Working off the current Shuttle ET Diameter core, the 27.5′ diameter core vehicle would be driven by Space Shuttle Main Engines (SSMEs) – utilizing existing RS-25D stock, prior to evolving to the less expensive (non-reusable) RS-25Es. The Upper Stage would be driven by RL10A4-3 engines.

Options to use 4 or 5 segment PBAN boosters, evolvable to HTPB, are also listed, likely referencing to a fast turnaround of a Block I configuration – whilst also showing how Tuesday’s test could technically be seen as highly valuable to a SD HLV.

“Recommendation: Accelerate the HLV decision – moderate HLV. Initiate a Shuttle-derived inline HLV Program beginning in FY2011. Initial 90 – 100 t range,” added the HEFT presentation. “Defer human rating and upper stage to Block II.”

Several major updates are expected over the coming months, although sources are noting that the focus is on the aforementioned Inline SD HLV, as opposed to an RP-1 or Sidemount SD HLV.

This can also be seen via work being conduced at the Marshall Space Flight Center (MSFC) – who have already been told they will lead the HLV project, along with splinter work into hardware evaluations, such as assessments into the use of spare Light Weight Tank (LWT) ET-94 at the Michoud Assembly Facility (MAF), which is leading the way to become the SD HLV Main Propulsion Test Article (MPTA).

As with the addition of STS-135, the conclusion and approval of political refinements into NASA’s future will be the key driver.

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STS-132 SRBs:

While Shuttle Derived Heavy Lift Launch Vehicle (SD HLV) options utilize the boosters that were set to live on via Ares I and Ares V, the need for “game changing” propulsion technologies has seen the solid’s stock weaken – with a potential drive towards all-liquid hydrocarbon vehicles.

Technically Ares lives on, with the US Congress holding the keys to approving the FY2011 proposal, which would result in the official cancellation of the Constellation Program – and while there will be at least two more shuttle missions, another solid will fire into life in Utah later this year, via the second firing of the five segment motor, known as DM-2.

Discussions are still taking place on adding one or two shuttle missions to the manifest, with the boosters for STS-335 (Launch On Need support for STS-134) already on site at KSC, potentially changing call signs to STS-135. However, as it stands, STS-134 will mark the final scheduled flight of the shuttle SRBs, when they will be tasked with aiding Endeavour’s two minute first stage ascent early next year.

Post flight IFA reviews are a key milestone for both the concluded mission, and the next scheduled flight – as their data provides the baseline for the Flight Readiness Reviews (FRRs). STS-133′s FRRs will enjoy smooth sailing from the standpoint of the SRBs, which performed admirably during Atlantis’ launch.

Only one IFA was recorded via the SRB IFA review – all 16 STS-132 IFA presentations available on L2 – relating to missing insulation from Forward Booster Separation Motor (BSM) Closeout – which is classed as an unacceptable debris hazard.

“RTV-133 Missing and Partially Debonded from Forward Booster Separation Motor (BSM) Closeout: Located on perimeter of upper right BSM – Size ~ 5 in long x ~ 1/4 in fillet bead. Unexpected debris source (not allowable),” noted the presentation, which added the loss of the insulation during ascent held no issue for the booster’s performance.

“Functions as environmental seal only. Not intended for thermal protection evaluation found heat effects and sooting not as severe as full flight but greater than adjacent area with intact RTV-133.”

Although its location is an unacceptable debris hazard, it is not clear if the material had enough mass to be a threat to the orbiter’s Thermal Protection System (TPS). However, no impact with the orbiter was noted, although an investigation is still ongoing as to the root cause of the liberation.

“Late ascent time of occurrence not ruled out – and also observed RTV-133 debonds associated with BSM closeout,” the presentation added. “IFA declared and Anomaly Resolution Team (ART-279) formed to investigate anomaly. Fault tree baselined and investigation ongoing.”

Squawks are minor issues which fail to be upgraded into a full IFA, with STS-132′s boosters listing nine – a low number – such items of interest in the review.

“132-002: System Tunnel Cover with Unknown Blue Material – No effect to hardware performance. 132-003: ET Attach Ring Forward Face Froth-Pak Foam Multiple Ascent Impact – No effect to system performance. 132-006: Range Safety System (RSS) Linear Shaped Charge (LSC) Connector Grease Intrusion – No effect to system performance,” listed the presentation.

“132-007 (x2): Corroded Coupling Nut on Aft Tunnel Cable Connectors – No effect to system performance. 132-008: Cracked Aft Beam on Frustum Aft Ring at -Y Isogrid Connection Point Splashdown time of occurrence. 132-009: Tape on Thrust Vector Control (TVC) Lower Frame – No effect to system performance.

“132-010: LH Rock and Tilt Auxiliary Power Unit (APU) Gearbox Quick Disconnect (QD) Cap O-rings Damaged Descent time of occurrence. 132-011: Shim Material Blistering on Hold Down Post (HDP) 1 No effect to system performance, Below Risk Assessment Mass.”

Squawk 132-002 provided a good example as to just how extensive the boosters are evaluated, even – in this case – before they launch, whist also showing how minor a squawk can be, with the blue material found to be nothing more than printer ink.

“Observed during L-1 day walkdown. Integrated SRB General Assembly Drawing Flag Note 0031 allows unavoidable processing material,” the presentation noted.

“Squawk generated to sample area, found material textured with multi-colored pattern. Compared to multiple sources Ball point pen, roller pen, laser printer ink and processing tap. Concluded most likely printer ink potentially transferred from Ground Operations processing tag. No effect to hardware performance.”

STS-132′s RSRMs:

The performance of STS-132′s RSRM set 111 was classed as within specifications and overall ‘excellent’, although their inspection process takes slightly longer, and involves evaluations once the motors have returned to ATK’s base in Utah. So far, no IFAs have been declared, as engineers push forward towards their +180 days report.

“All RSRM countdown parameters were within LCC (Launch Commit Criteria/OMRS limits and within family,” opened the ATK presentation to the STS-132 IFA review (L2). “Overall performance of both RSRM motors and all ATK BSMs excellent and well within requirements.

“RSRM postflight hardware evaluation is ongoing: KSC – in work. Aft BSM and RH field joint assessments still to be performed. Utah – in work. Nozzle joint disassembly complete. No IFAs declared at this time.”

Only four squawks – two related to the same issue – were written, all of which have been reviewed and classed as no impact to the performance of the hardware.

“Overall performance of both STS-132 (RSRM-111) motors and ATK BSMs were excellent. Postflight evaluation is still in work. Four squawks have been written at this time. No IFAs declared at this time but additional postflight disassembly and evaluations are still in work,” added the introduction.

Two of the squawks were charged against the Left Hand (LH) Booster Separation Motor (BSM), relating to insulator-to-closure edge unbonds on serial numbers 232 and 233. Due to the lack of debris or motor performance concerns, this issue was not elevated to become an IFA.

The issue is also classed as likely to have occurred during splashdown in the Atlantic ocean, as opposed to during any phase of the powered ascent of first stage flight.

“Creation and growth of unbonds during post-operation heat soak and splashdown is expected,” noted the presentation. “No mechanism exists for creation of unbonds prior to post-operation heat soak.”

The third issue related to the Right Hand (RH) Nozzle Leak Check Barrier O-ring Groove on the Aft Edge Corner – which suffered from phenolic damage. No compromise to joint performance was noted.

“A small area of damage to the RH nozzle-to-case leak check barrier O-ring groove aft corner was observed at 308 degrees,” noted the presentation, which added the cause is still being investigated.

“Cause determination is still in work but loss is not expected to compromise thermal barrier capability of the leak check barrier O-ring or decrease the expected joint performance in the event of pressure reaching the leak check barrier O-ring.”

The final note on the IFA presentation referenced a blister on the insulation associated with the Right Hand Igniter Chamber. The blister was noted as a manufacturing defect with no impact to igniter performance.

“Unusually shaped feature (roughly 0.5” by 2”) was noted on the ID of the RH igniter chamber. Squawk was written to permit evaluation,” the presentation continued.

“A portion was excised which verified the observation was a blister and had no signs of thermal effects or sooting. Engineering allows blisters of this size in this region of the igniter.”

As with the orbiter and External Tank (ET) IFA reviews, the performance of the shuttle hardware has been highly impressive over recent years, at the very least ensuring the Space Shuttle Program (SSP) goes out on a high, or potentially vindicating the faith of lawmakers – should they approve funding to allow the program to continue through as far as 2012.

Proof the shuttle’s recent performance has been recognized by the engineering and political communities can also be seen via such extension debates, which now focus mainly on cost, as opposed to safety concerns.

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STS-132 Pad Flow Latest:

With excellent timing, engineers cleared the outstanding IPR (Interim Problem Report) relating to the calibration of a sensor, while the only new IPR over the past few days – associated with the Left Reaction Control System (LRCS) – is of no issue for the flow.

“Partial Pressure Oxygen (PPO2) sensor C calibration was completed on Friday. The sensor is functioning nominally,” noted the NASA Test Director (NTD) processing report on L2. NEW IPR 0039: LRCS fuel tank ullage pressure regulator A locked up at 269 psi should be no more than 268 psi. Under engineering review (cleared).”

With the regulator deemed to be in a good condition, engineers completed S0071 operations to pressurize the systems for flight, which was followed by the closure of Atlantis’ Payload Bay Doors (PLBDs) for the final time ahead of launch.

“S0071 Main Propulsion System (MPS), Space Shuttle Main Engine (SSME), Orbital Maneuvering System (OMS) and Reaction Control System (RCS) helium and nitrogen tank pressurization for flight is complete,” added the flow report.

“Payload Bay Doors (PLBD) were reopened yesterday for crew sharp edge inspection and Orbiter/Payload Vertical Closeout, and closed for flight.”

S0007 Launch Countdown preps worked through a nominal flow towards Call To Stations (CTS), 30 minutes prior to the start of the count – which began at 4pm Eastern.

STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-132/

Changes to STS-132 RSRMs:

When Atlantis launches, the STS-132 stack will boast two changes to the RSRMs (Reusable Solid Rocket Motors): a new fluorocarbon O-ring V1288 in nozzle joints 4 and 5 and the incorporation of V1288 O-rings in the Igniter Gaskets.

In terms of the Nozzle Joints, “Incorporated V1288 fluorocarbon O-rings in nozzle joints 4 and 5,” notes the RSRM portion of the SPP (Space Shuttle Program) FRR from April 28 – a presentation available for download on L2.

This replacement of the old V1247 O-ring design with the new V1288 design is part of an ongoing replacement process made necessary by the obsolescence of the old V1247 O-ring design – an obsolescence that mandated a requalification of a V1247 ingredient or the creation of a new O-ring design.

Since a new material (dubbed V1288) as available after its creation to “[improve] resiliency … for field joints,” it was decided that using the V1288 material would simplify the manufacturing process for the supplier while increasing safety at the nozzle joints.

Approval for the new V1288 O-rings for nozzle joints 4 and 5 was certified based on the material properties of the V1288 being equal to or greater than the V1247 as well as the fact the “2x tracking requirement still met for joint no. 5 (dynamic).”

Moreover, the new V1288 O-rings decrease the erosion rate at the nozzle joints.

The V1288 O-rings were flaw tested in field joints on FSM-12 (Flight Support Motor 12) and FSM-13 out in Utah. The V1288s were also successfully tested in nozzle joints 4 and 5 on the Ares DM-1 (Demonstration Motor 1) and FSM-17.

The V1288s have also been successful flown in BSMs, RSRM field joints, RSRM nozzle-to-case joints, and RSRM nozzle joint #1 on previous Shuttle flights.

As such, the new O-rings in nozzle joints 4 and 5 are safe to fly on STS-132 and subsequent flights.

The second change to debut on STS-132′s RSRMs is the incorporation of the V1288 O-rings in the Igniter Gaskets.

“Replaced V1944 (V1247 with paraffin release agent) fluorocarbon seal material with V1288 fluorocarbon seal material in Inner, Outer, and Safe & Arm (S&A) gaskets,” notes the SSP FRR RSRM presentation.

Furthermore, the adhesive in the gaskets was changed for the STS-132 RSRMs from Chemlok 5150/607 to Chemlok 8116.

The reason behind this change also comes from the obsolescence of a V1944 (V1247) ingredient that required a requalification or a new material (Chemlok 8116) “specifically designed for peroxide cure elastomers.”

The new material (Chemlok 8116) and integration of the V1288 O-rings were verified for flight based on the fact that the metal retainer design, material, and fabrication processes were not changed from the previous design.

Furthermore, the physical dimensions of the gasket sealing elements were not changed and the material properties of the V1288 material “[met] specification requirements for V1944″ and have been shown to be better than or equivalent to the V1944 O-rings.

Tests on the compression-set of the new design support all stack-life and age-life requirements. Moreover, numerous bounding dynamic pressure tests indicate that the sealing capability of the V1288 O-ring gaskets is “better than V1944 gaskets with the 1.4x tracking requirement still met.”

Retainer-bond-seal system tests also indicate greater than or equal to performance from V1288s and “static tests and 70-lb char motors show improved erosion rates for V1288s.”

The safety and operation of the new design for V1288 S&A and inner gaskets were demonstrated on LAT 85-A and 85-B.

The S&A gaskets were further verified during the static test firings of TEM-13 (Technical Engineering Motor 13), FSM-15, Ares DM-1, and FSM-17 without issue.

As such, STS-132 and subsequent flights are safe to fly with the new igniter gaskets seal design.

STS-131 SRB IFA Review and Forward Action/STS-132 SRB Nonconformance Review:

Following the highly successful STS-131 mission by orbiter Discovery last month, the standard IFA review of the entire vehicle revealed only one issue with the SRBs on that flight.

“In-Flight Anomaly (IFA) STS-131-B-001 RH Data Acquisition System (DAS) Failed to Record Full Flight Accelerometer Data,” notes the SRB presentation to the SSP FRR at the end of April.

According to the SSP FRR presentation, the DAS (serial number 2000003) did not record full flight accelerometer data.

During a post-flight data review, it was discovered that the full flight data was not recorded due to “insufficient time left in memory,” notes the SRB presentation.

In all, the DAS recorded 540-seconds of accelerometer data – with 446-seconds of the data coming from pre-flight testing. After this ground testing was complete, the DAS was not reinitialized, leaving only 94-seconds of memory remaining for in-flight recording.

Despite the failure to record all the accelerometer data, there was no concern for the crew or the mission because of the loss of full data, nor is there an increased concern for the STS-132 crew or mission as the loss of accelerometer data is a Criticality 3 concern.

Nonetheless, to ensure that this problem does not reoccur, a new Preflight Test Procedure Reset will be required if a DAS unit is powered up before the final g-switch activation. Furthermore, “Track power on time for g-switch activation to ensure sufficient memory available for flight” will also be performed notes the presentation.

In addition to this potential change for STS-132′s SRBs, there were (at the time of the SSP FRR on April 28) 3 open problem reports, or nonconformances, with the STS-132 SRBs.

These nonconformances – all of which will be managed or accepted as is with paperwork before launch – include a discrepancy in the Bolt catcher Thermal Protection System width dimensions, a DAS unit access plate Changeout, and an unapproved electrolyte and neutralizer performance in an Auxiliary Power Unit (APU) part.

In all, the STS-132 stack’s SRBs and RSRMs have been cleared for flight on Friday with Atlantis on the 34th Space Shuttle mission dedicated to construction and outfitting of the International Space Station.

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STS-131 Processing Latest:

Discovery remains in a nominal flow towards the April 5 launch date target, as processing milestones continue to be reached with a few days of contingency still in the team’s back pocket. The latest milestone came via the installation of the STS-131 payload.

“OV-103 / ET-135 / SRB BI-142 / RSRM 110 (Pad A): Payload installation into the orbiter was successfully completed. Electrical connections (in work). Payload Integrated Vehicle Testing operations are planned for Friday,” noted the NASA Test Director (NTD) processing latest (L2).

“S1287 Aft compartment closeout for flight continues with completion planned Friday. SCAPE (Self-Contained Atmospheric Protection Ensemble) operations to drain the liquid separator were completed Wednesday. Two waves of LH2 tankers will replenish the LH2 sphere.”

A small Problem Report (PR) was charged to the processing flow, and resolved by the time of the latest processing report, although a second cracked tile has been found during inspections of Discovery’s ceramic inserts – which is undergoing engineering evaluations.

“PR 5547 was taken for a crushed convoluted tubing adjacent to connector in the aft compartment. Repair and retest was completed. An additional tile was discovered cracked on window 6. Engineering evaluation is in work,” added the report, noting the ceramic insert inspections are continuing on other areas of the orbiter, for the purpose of flight rationale.

“Payload Bay Door hinge line ceramic insert engineering evaluation and flight rational development continues.”

An outline on the FRR effort relating to the inserts will be provided on Friday, along with the status of the other items of discussion.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

SRB RGA Item of FRR interest:

Each SRB contains two of the RGAs, with each RGA containing one pitch and one yaw gyro. These provide an output proportional to angular rates about the pitch and yaw axes to the orbiter computers and guidance, navigation and control system during first stage ascent flight in conjunction with the orbiter roll rate gyros until SRB separation.

At SRB separation, a switchover is made from the SRB RGAs to the orbiter RGAs.The SRB RGA rates pass through the orbiter flight aft multiplexers/ demultiplexers to the orbiter GPCs (General Purpose Computers). The RGA rates are then mid-value selected in redundancy management to provide SRB pitch and yaw rates to the user software. The RGAs are designed for 20 missions.

No issues have be reported with the RGAs for several years, until a test failure this month led to an effort to clear the related units for the flight of Discovery’s boosters.

“Observation: SRGA s/n 119 failed Yaw Drift Insensitivity (DI) during pre-installation checkout at the Assembly and Refurbishment Facility (ARF). SRGA s/n 119 failed Pitch Null Offset after passing incoming functional test procedure,” noted a presentation (L2) reviewed by Tuesday’s Space Program Requirements Control Board (PRCB) meeting.

“Concern: Similar failure during (STS-131) ascent could cause erroneous output data from an SRGA.

“Background: SRGA s/n 119 failed Yaw (DI) during 6-position test at ARF on March 1-3, 2010. 1st and 3rd test runs failed, 2nd run passed. s/n 119 failed Pitch Null Offset was observed following incoming functional test procedure. s/n 119 last flew on STS-126, November 14, 2008 (without issue).

“Original design of SRGAs experienced failures of cracked pivots, resulting in a subsequent change of damping fluid (from silicone oil to Krytox oil) and gyroscope materials. SRGA design uses newer ‘Krytox’ gyro, replacing older ‘silicone’ gyro design to reduce vulnerability to shock load induced damage to pivots.

“The PRCB restricted silicone SRGA usage to single flights in June 1987. Krytox design modification development study was authorized in May 1990. Krytox gyros were phased in between STS-70 7/13/95 (1 Krytox gyro in slot 4) and STS-69 9/7/95 (Krytox gyros in all 4 slots).”

Flight history and risk assessment – along with the redundancy in the system – all played a part in aiding the path towards gaining flight rationale for STS-131, while engineers will spend additional team carrying out further checks for downsteam missions in an effort to understand root cause and any potential foward work.

The option to replace the unit(s) at the pad was available, although a there was a slight risk this would push out the launch date by a number of days. This would have been an unlikely option to take, given the confirmed health of Discovery’s SRB RGAs.

“SRGAs with Krytox gyros were certified by test for 24 pyro shocks. No Krytox Gyro pivot/bearing failures since 1995 upgrade. Only one previous Krytox gyro failure of 6-position test, attributed to FOD in bearing. Four SRGAs for redundancy,” noted the risk assessment portion of one of the three main presentations on the problem.

“Criticality 1R/2 for erroneous output; Criticality 1R/3 for loss of output. Hazard: B-00-17, Loss of Vehicle Control. Controlled; Catastrophic, Improbable. SRGAs are tested every flow.

“Schedule Risk: SRGA can be R&R’ed at Pad, requires several shifts. Severity is slight schedule slip (2). Likelihood of failure is Unlikely (2). Mission Safety: Severity is Catastrophic (5). Likelihood is Highly Unlikely (1). Requires multiple failures.”

Given the unit which suffered the problem is not part of the STS-131 stack, along with a good track record for the units that will fly with Discovery’s boosters, flight rationale is already in place ahead of Friday’s Agency FRR.

“Flight rationale for STS-131: All STS-131 SRGAs passed functional test prior to installation into forward skirt (required within 120 days of installation). Verifies flightworthiness between flights. 6-position test is used to test for pivot failures. Shock loads (contribute to pivot failures) do not occur between 6-position test and launch,” the presentation noted.

“STS-131 SRGA ARF test data nominal. SRGA tested during ARF forward skirt Assembly Checkout (ACO), Vehicle Assembly Building (VAB) Shuttle Interface Test (S0008), Terminal Countdown Demonstration Test (S0017) and prelaunch checkout (S0007) at T-3 hours.

“SRGA system is redundant by design. Criticality 1R/2 for erroneous output. Fault Detection Isolation and Recovery (FDIR) deselects first failed SRGA during ascent. Interchangeable Mid-Value Select (IMVS) selection filter rejects failed signals.”

As noted by the presentation, the RGAs will recieve a final health check at T-3 hours in the countdown, although it is highly unlikely they would become a problem given their track record.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

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