Prediction Spacecraft Pressures during Launch

Abstract

Every spacecraft must vent all enclosed air during launch or else risk a structural failure due to the resulting differential pressure. For this reason, guidelines for providing vent paths are typically part of the spacecraft requirements documentation. These guidelines, however, are often limited to a specific venting configuration, and engineering judgement must be applied to determine whether any other venting scheme meets the requirement. Many spacecraft now require screens and/or labyrinth structures at vent ports to prevent any contained particle contamination from exiting with the venting air. The flow losses through such structures cannot easily be compared to that through an open vent hole. This paper describes testing and analysis that has been conducted, given a pressure decay profile external to the payload fairing, to accurately determine differential pressures during launch for any vent configuration, including that associated with honeycomb panels. Testing of flow through representative vent screen materials has been characterized resulting in empirical algorithms for simulating vents of any size. The technique has been verified by comparison to pressure measurements made from a representative honeycomb radiator panel.