Gust models for launch vehicle ascent

Abstract

Assessments of elastic body and buffeting response to inflight atmospheric disturbances or gusts are important in the establishment of vehicle design structural requirements and operational capability. Launch vehicles can have significant response to gusts that are not measurable with typical launch site winds aloft measurements such as the Jimsphere wind profile measurement system or the 50 MHz Doppler Radar Wind Profiler (DRWP) used at Kennedy Space Center (KSC) in support of the Shuttle and DOD launch programs. It is not practical to perform elastic body loads analyses on the day-of-launch (DOL) because gusts are transient with time duration measured in seconds. (However, rigid body loads simulations are performed on DOL using measured Jimsphere wind profiles.) Thus, the commit to launch decision must be protected for gust uncertainty contributions to elastic body loads uncertainties. Discrete gust models used for establishment of trajectory and loads increments that account for launch vehicle elastic body and buffet response uncertainty on the day of launch are described. The origin and shortcomings of the classical NASA 9 m/s discrete gust model are discussed. A new discrete gust model that includes variation of gust magnitude as a function of altitude and gust length is presented for use in the establishment of vehicle elastic body and buffet response uncertainty on DOL.