Description of Driving Event:
Environmental Regulations Resulting in Manufacturing Process Changes for RSRM
Lesson(s) Learned:
Changes in the Pressure Sensitive Adhesive (PSA) and the cleaning agent for the J-flap of the RSRM were driven by environmental regulations. The certification testing for these changes included a Flight Support Motor (FSM) firing without the application of side loads, a significant condition for RSRM field joints for which the J-flap plays a role.
Recommendation(s):
Employ the application of side loads in all future RSRM FSM firings.
Evidence of Recurrence Control Effectiveness:
The SSP and RSRM project agree with this recommendation when aft field joint test objectives warrant inclusion on an FSM test motor. During Space Shuttle return-to-flight RSRM redesign, the assessment of strut loading on the solid rocket motors concluded that the only influence was at the aft field joint. The influence on the aft field joint gap openings was predicted to be less than 0.001 inch, roughly an order of magnitude less than the contribution of the internal motor pressures. Side loads were included on two RSRM static test motors (QM-7 and -8) in a comprehensive effort to include every element of flight loading influencing the aft field joint gap openings. Joint gap openings were not measured directly, but the sealing systems performed as expected. Gap openings were measured on the RSRM structural test article-3, where testing showed side loads influence to be less than 0.0005 inch out of a total of 0.0084 inch for aft field joints only. The consideration to include side loads on all future tests would not come without technical penalty. To accommodate the side load forces, the aft test stand must be locked out, and as such, no thrust measurements are obtained. Also, no thrust vector control (TVC) duty cycling is performed during the side load events, which requires modification to the baseline static test duty cycle; for certain test objectives, this is an important requirement consideration. This baseline TVC duty cycle is utilized to allow direct performance comparisons between static tests, primarily associated with nozzle and aft dome materials or components. Therefore, a generic inclusion of side loads on all future FSM tests would require elimination of other test considerations, which, depending on specific test objectives, might be a qualification necessity. In conclusion, the RSRM static test policy includes side loads on full-scale static test motors where there are test objectives associated with the aft field joints, which could be influenced by side loads.
Documents Related to Lesson:
N/A
Mission Directorate(s):
- Space Operations
- Exploration Systems
Additional Key Phrase(s):
- Aerospace Safety Advisory Panel
- Environment
- Energy
- Ground Operations
- Hazardous/Toxic Waste/Materials
- Policy & Planning
- Safety & Mission Assurance
- Test & Verification
Additional Info:
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