{"id":39505,"date":"2014-09-15T17:12:13","date_gmt":"2014-09-15T09:12:13","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/atk-making-progress-on-srb-propellant-void-issue\/"},"modified":"2014-09-15T17:12:13","modified_gmt":"2014-09-15T09:12:13","slug":"atk-making-progress-on-srb-propellant-void-issue","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/atk-making-progress-on-srb-propellant-void-issue\/","title":{"rendered":"ATK making progress on SRB propellant void issue"},"content":{"rendered":"

A year after discovering small voids between the solid propellant and the outer casing of the aft segment of a test motor for the massive 5-segment SRBs for NASA\u2019s upcoming Space Launch System (SLS) rocket, ATK is making firm progress in their investigation and the mitigating factors toward correcting the issue ahead of the Qualification Motor -1 (QM-1) firing.
\nBackground:<\/p>\n

Solid rocket motor designs utilize a specialized rubber insulation between the external case and the propellant.<\/p>\n

The bond between the propellant and insulation, which provides thermal protection for the case, is a critical design feature that undergoes rigorous x-ray inspection to assure its acceptability for flight. These inspections are conducted on all solid rocket motors to ensure they are free of defects.<\/p>\n

\"GroundIn the late fall of 2012, as ATK was preparing for the first Qualification Motor (QM-1) test of the new 5-segment variant of the Space Shuttle\u2019s Solid Rocket Boosters (SRBs), small voids between the propellant and the motor casing of the aft segment were discovered during standard x-ray inspections to evaluate an insulation lining material change in the SRB motor segments.<\/p>\n

The solid rocket motor segments have a layer of insulation with a liner coating to form a contiguous bond with propellant (known as the bond line). Voids at the propellant bond line are readily detectable with x-ray inspections, and when found during the SLS inspection led to a change in the Propellant\/Liner\/Insulation (PLI) manufacturing process.<\/p>\n

\"2014-09-14ATK, with NASA\u2019s approval, rejected the first QM-1 aft segment and proceeded to recast another to ensure that the voids would not interfere with the test objectives of QM-1. However, the second test article had similar voids, leading ATK and NASA to investigate the new rubber insulation material.<\/p>\n

\u201cWe had adequate schedule margin when the voids were discovered to do a thorough evaluation of the voids. We felt this was important to ensure we could determine a root cause and take corrective action,\u201d said Harry Reed, deputy program manager, ATK 5-Segment Booster program \u2013 to NASASpaceFlight.com<\/p>\n

With two aft segments now displaying the same issue, ATK expanded their investigation to determine what was causing the propellant to de-bond from the casing wall and form voids.<\/p>\n

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Quickly, evidence began to mount that the issues were related to use of a new material in the insulation lining between the propellant and the motor casing wall.<\/p>\n

\"2014-09-14Originally, the Shuttle SRB motor segment insulation lining was made of chrysotile-filled rubber: chrysotile being the most-common mineral form of asbestos.<\/p>\n

While asbestos minerals contain useful sound absorption, strength, and resistance to fire, heat, electrical, and chemical damage properties, the silicate mineral holds severe health risks when inhaled over a prolonged period of time.<\/p>\n

Over the last decade, the removal of asbestos products in ATK deliverables \u2013 specifically in the insulation linings of the SRBs \u2013 had been a stated priority of the company.<\/p>\n

So high was this priority that non-asbestos (chrysotile-free) rubber insulation was on a path to be qualified for use on the Shuttle SRBs \u2013 even though that particular kind of insulation never flew before the end of the Shuttle Program in 2011.<\/p>\n

\"\"Nevertheless, the qualification efforts for flight on the Shuttle SRBs meant that the new insulation material had been thoroughly tested through numerous static test firings of SRBs at ATK\u2019s proving ground near Promontory, Utah.<\/p>\n

With qualification ground testing complete, chrysotile-free insulation was then baselined for use on the Ares I rocket. After that rocket\u2019s cancellation, the baseline use shifted to the SRBs for the SLS rocket.<\/p>\n

Thus, the switch to chrysotile-free insulation was made, and the old asbestos-containing liners were rendered obsolete upon the retirement of the Shuttle fleet.<\/p>\n

\"2014-09-14As development of the SLS 5-segment SRBs continued between 2011 and 2013, three DM (Demonstration Motor) tests were carried out \u2013 all of which occurred with the new insulation and without out-of-family void issues.<\/p>\n

As the SLS booster design matured from the DM stage to the QM, standard development processing and design changes were undertaken as the SRB design moved toward flight status.<\/p>\n

However, after the DM series of static test firings was complete, NASA initiated a request that ATK conduct additional inspections on the QM series of motors segments to see if any defects were present as a result of the switch to asbestos-free insulation lining.<\/p>\n

The investigation:<\/p>\n

Following the x-ray discovery of the voids within the propellant of the two aft QM-1 motor segments, ATK placed segment processing on hold until an investigation could determine primary\/root cause(s) and corrective actions.<\/p>\n

With confirmation of a PLI unbond and propellant void, ATK began a \u201cdeep dive assessment in support of Knowledge Point Share\u201d meetings with NASA to determine the root cause of the PLI unbond and void issue.<\/p>\n

At an initial meeting with engineers from the Marshall Space Flight Center, the investigation team prioritized the dissection of the QM-1B segment, the one that showed signs of an unbond, as the first site for a PLI sample extraction and detailed examination.<\/p>\n

\"SlideMoreover, ATK and NASA agreed to cast an aft segment \u2013 with added scrutiny \u2013 following the DM-series manufacturing processes, not the QM-series manufacturing processes, to assess whether the PLI void issue was due to an unidentified effect of manufacturing changes. These activities were a part of the root cause investigation.<\/p>\n

This DM series segment received the name Process Simulation Article-1 (PSA-1).<\/p>\n

By November 2013, ATK had finished PSA-1 aft dome\u2019s cure, trim, and finalization and had begun insulation lay-up of the barrel section.<\/p>\n

Additionally, ATK had begun constructing an Integrated Logic Flow (ILF) to outline all of the testing (sub-scale and full-scale) and key decision points necessary for the down-selecting of changes to be incorporated on the Process Simulation Article-2 (PSA-2, full scale aft segment, loaded with live propellant) \u2013 which would follow a new-and-improved QM motor production process fine-tuned over the course of the root cause investigation.<\/p>\n

By the end of 2013, PSA-1\u2019s insulation cure was complete, and Ultrasonic Testing (UT) inspections revealed the presence of a void in the insulation by the aft dome factory joint.<\/p>\n

Follow-up x-ray inspections showed the void to be three small voids in close proximity.<\/p>\n

This discovery provided valuable corollary data to inspection results of Shuttle and Ares I DM series motor segments where voids had been detected in the same area of aft segment motors (again, all within family for DM series motors).<\/p>\n

\"PLI\"As the investigation continued into March 2014, ATK\u2019s Evaluation Article-1 (EA-1) \u2013 designed to allow for comparison testing of insulation lay-up techniques used inthe current QM series motor production process (used in Joint 1 of EA-1) and newly-identified insulation lay-up techniques (used in Joint 2) \u2013 had completed x-ray evaluations.<\/p>\n

These x-rays revealed that Joint 2 (using the newly identified lay-up technique known as wallpaper butt-joints) was clear of any voids.<\/p>\n

However, Joint 1 was shown to possess two small voids in a location where the area of the seal ply insulation overlaps the joint.<\/p>\n

With these results in hand, the investigation teams made the recommendation to use the new wallpaper butt-joint lay-up process on EA-1\u2019s 3rd Joint: a Joint upon which the engineering teams had forgone insulation lay-up until evaluations on the two lay-up options could be completed and evaluated.<\/p>\n

See Also<\/h4>\n