The United Launch Alliance Delta IV vehicle − an update to the pulse settling propellant management approach

Abstract

During the flight readiness review process of a recent Delta IV mission, an independent review team from Analex Corporation presented results of simulations of the behavior of the second-stage cryogenic propellants. These results differed considerably from those Boeing and the Aerospace Corporation were showing at the time. A team consisting of representatives from Boeing, the Air Force, the National Reconnaissance Office − Office of Space Launch (NRO/OSL), the Aerospace Corporation, Flow Sciences, and Analex investigated this slosh behavior and was chartered to resolve the discrepancy between analysis results. During the investigation, it was concluded that the slosh behavior of liquid hydrogen (LH₂ ), during the second stage coast phase of flight, would not be constrained to the aft end of the tank and thus presented an increased mission risk. The presence of propellant in the tank forward dome at tank venting could lead to propellant ingestion into the vent/relief system and result in a thrust imbalance. This paper is an update to a paper previously released [1] that focused on the team's investigative efforts and resolution of the issues associated with the sloshing, including the implementation of a pulse-settling approach for propellant management. The update (italicized text) includes a discussion of the flight validation of the successful launches that implemented pulse-settling. Figure 1 is a screen-shot from a simulation of the LH₂ sloshing in the second-stage tank during a coast period.