Operating Deflection Shapes for the Space Shuttle Partial Stack Rollout

In November of 2003 a rollout test was performed to gain a better understanding of the dynamic environment for the Space Shuttle during transportation from the Vehicle Assembly Building to the launch pad. This was part of a study evaluating the methodology for including the rollout dynamic loads in the Space Shuttle fatigue life predictions. The rollout test was conducted with a partial stack consisting of the Crawler Transporter, Mobile Launch Platform, and the Solid Rocket Boosters with an interconnecting crossbeam. Instrumentation included over 100 accelerometers. Data was recorded for steady state speeds, start-ups and stops, and ambient wind excitations with the vehicle at idle. This paper will describe the operating deflection shape analysis performed using the measured acceleration response data. The response data for the steady state speed runs were dominated by harmonics of the forcing frequencies, which were proportional to the vehicle speed. Assuming a broadband excitation for the wind, analyses of the data sets with the vehicle at idle were used to estimate the natural frequencies and corresponding mode shapes. Comparisons of the measured modal properties with numerical predictions are presented. INTRODUCTION The Space Shuttle Orbiter is mated to the External Tank (ET) and Solid Rocket Boosters (SRBs) on top of a Mobile Launch Platform (MLP) in the Vehicle Assembly Building (VAB). A Crawler Transporter (CT) [1] is used to lift the nearly 12 million pound MLP-Space Shuttle assembly and carry it to one of the two launch complexes, which are approximately 3 to 4 miles away. The average duration of the transportation process is 6.4 hours with the CT reaching top speeds of 0.9 miles per hour. A test was conducted in November of 2003 to gain a better understanding of the dynamic environment and to evaluate the methodology used to develop load spectra associated with the rollout mission phase for certification of Space Shuttle Orbiter life. Figure 1 shows the partial stack test configuration used in the November 2003 test. This configuration has the MLP with the loaded SRBs and External Tank (ET) cross beam on the CT. Acceleration, strain, wind, and hydraulic pressure measurements were acquired during the transport process. Data was collected for variations in CT operations including starts, stops, turns, speed variations, and ambient wind excitations with the CT at idle to evaluate the sensitivity of the response to the input forcing frequency. This report will focus on the operating deflection shape (ODS) analysis of the 111 channels of accelerometer data. Assuming a broadband wind excitation for the CT idle data sets, the ODS analyses were used to estimate the natural frequencies and mode shapes for numerical model validation. The test setup, CT operating conditions, ODS results, and comparisons with the numerical predictions are presented. Figure 1. Partial stack rollout test. Figure 2. ODS measurement model. 26,30 27,31 28,32