24 J. Sills et al. Fig. 3.8 VSS Tangential Strut Damping Force due to 6 in. Twang (linear vs nonlinear) Fig. 3.9 (Left) EC and MM Positioning on the East Underside of the ML at Launch Pad, (Right) EC Concept 3.6 Liftoff Pad Separation Twang – Release of Preloads The transient contribution (twang) and decay characteristics of the stacking and cryo-induced preloads is of considerable interest to the SLS program. For this, the DGS algorithms work alongside the Henkel-Mar pad release algorithms to ensure a physics-based approach to pad release and the relief of preloads. It is important to note that not all ML/booster interfaces separate at the same time; therefore, the release of strain energy due to preloads must be congruent with the sequence of separating DoFs. The DGS approach is designed for this to occur in an automated physics-based fashion. Figure 3.10 provides the forces in the upper and lower aft struts from a SLS liftoff transient CLA. The DGS enforced initial conditions, Henkel-Mar pad separation, and the joint workings of the two algorithms results in a “twang” at booster separation which is clearly seen. Figure 3.11 provides the right booster/CS forward attach time-history in the longitudinal direction again clearly demonstrating the impact of the strain relief of the “toe-in” loads. Figure 3.12 provides the EC interface forces in the longitudinal direction. From this figure, it is seen that for the scenario simulated, the forces stays positive (i.e., in contact) after the vehicle separates from the pad.
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