Analysis of in-flight winds and Shuttle aerodynamic load indicators

Abstract

Wind profile assessments prior to launch contribute to the shuttle commit to launch decision. Wind profile extremes (positive or negative) for wind components, vertical shear of wind components and wind component change with respect to time are evaluated during the countdown relative to limits established from prior analysis of wind profile data bases used for the Shuttle design. Vehicle aerodynamic load indicators and loads at specific points on the vehicle are assessed with trajectory and rigid body loads simulations using the scheduled wind profile measurements at 6.25, 4.25 and 2.0 (hours) and at 70 minutes prior to launch (except not for Mir or Space Station at T-70 minutes). When a trajectory and loads simulation is not available, it is assumed that a wind profile anomaly is an accurate predictor of a vehicle load indicator anomaly; this is the basis for requiring an unscheduled trajectory and loads analysis at 3 hours prior to launch. At any time during the countdown, if the out-of plane wind component shear exceeds the largest shear in the shuttle design verification data base (a set 1800 Ximsphere wind profiles), a special study is initiated to revise the allowance made for the orbiter tail dynamic response to gust, which is not simulated on the day of launch. An alternate method based on a power spectrum density model and spectrum analysis of day-of launch wind profiles is proposed for triggering this study. Present methods for identifying selected wind profile anomalies are examined. Concepts are described for estimation of aerodynamic load indicator variables from wind variables for application when trajectory simulations are not available (3 hours prior to launch when a Jimsphere profile is measured only as a backup in case of a problem with the T-4.25 hour profile used for the commit to launch decision, or at any time during the countdown based on radar wind profiler data at 15 minute intervals.) The application for this estimation procedure is to provide justification for non-scheduled trajectory and loads simulations and reexamination of the commit to launch decision.