BUCKLING TESTING AND ANALYSIS OF SPACE SHUTTLE SOLID ROCKET MOTOR CYLINDERS

AIAA-2002-1529BUCKLING TESTING AND ANALYSIS OF SPACE SHUTTLE SOLID ROCKET MOTOR CYLINDERSSubmitted to the43 _dAIAA/ASME/ASCE/AHSStructures, Structural Dynamics & Material ConferenceDenver, CO April 22-25, 2002Thomas J. WeidnerATK Thiokoi PropulsionA Division of ATK Aerospace CompanyDavid V. LarsenATK Thiokol PropulsionA Division of ATK Aerospace CompanyABSTRACTA series of full-scale buckling tests were performed onthe space shuttle Reusable Solid Rocket Motor (RSRM)cylinders. The tests were performed to determine thebuckling capability of the cylinders and to provide datafor analytical comparison. A nonlinear ANSYS FiniteElement Analysis (FEA) model was used to representand evaluate the testing. Analytical resultsdemonstrated excellent correlation to test results,predicting the failure load within 5%. The analyticalvalue was on the conservative side, predicting a lowerfailure load than was applied to the test. The resultingstudy and analysis indicated the important parametersfor FEA to accurately predict buckling failure. Theresulting method was subsequently used to establish thepre-launch buckling capability of the space shuttlesystem.INTRODUCTIONThe RSRM used in the space shuttle launch system ismade up of twelve thin wall steel cylindrical segments(see Figure 1). During pre-launch, launch and liftoff,the two RSRMs support the entire space shuttle liftoffvehicle. Bolts with nuts, that are severed by smallexplosives (frangible nuts), hold the aft end of theRSRMs fixed to the Mobile Launch Platform until justprior to liftoff. To ensure that the shuttle does not driftinto any part of the Mobile Launch Platform, the spaceshuttle main engines are started approximately sixseconds prior to liftoff. During the pre-launch phase ofliftoff the space shuttle main engines produceapproximately one million pounds of thrust. TheRSRMs respond to this load by initially bending alongthe motor, resulting in a 26 inch displacement at theRSRM nosecone and then rebounding back to the1original upright position. As soon as the vehicle hasreturned to the upright position, the frangible nuts aretriggered, freeing the shuttle for liftoff with enoughlateral inertia to ensure safe ascent without thepossibility of impact on the Mobile Launch Platform.The initial bending during pre-launch generates asignificant structural load on the RSRMs. The severityof this loading condition is further complicated by thelack of internal pressure to support the thin wall of theRSRM cylindrical membrane. At this point during thelaunch, buckling becomes a significant concern. Inorder to avoid the possibility of a buckling event,several parameters (wind speed and direction, payload,membrane thickness and imperfection, etc.) arerestricted, and stringent liftoff vehicle configurationrequirements have been established. As iiftoffrequirements become more restrictive, the probabilityof buckling is reduced, however, the probability of alaunch delay or cancellation is increased. One of theprimary concerns is wind. High wind speed cansignificantly increase the horizontal load and the totalbending load (see Figure 1). Therefore, wind speed anddirection are closely monitored prior to lift-off.Using a conservative linear eigenvalue analysis todetermine the RSRM's buckling capability resulted inwind speed allowables more restrictive than necessary.As the space shuttle program has developed, severalmodifications have been incorporated to improveperformance and efficiency. As part of an enhancementactivity, significant effort has been invested in trying todecrease the probability of a launch abort or delay dueto wind speed concerns.It is a common practice in industry to use eigenvalue-buckling analysis to establish preliminary designparameters. The basic structure is analyzed using theAmerican Institute of Aeronautics and AstronauticsCopyright ©2002. ATKThiokol Propulsion.a DivisionofATKAerospace Company, Published by the American Institute of Aeronauticsand Astronautics with Permissionhttps://ntrs.nasa.gov/search.jsp?R=20020090804 2020-05-17T15:42:29+00:00Z