Current operational practice for the Delta second stage

Abstract

At the end of operation for the Delta launch vehicle's second-stage propellant tankage, 250 lb of propellants remain. Analyses of on-orbit breakups that may have been caused by fuel tank overpressurization have led to the adoption of a restart operational policy in which the engine is fired for as long as necessary to ensure that as much oxidizer as possible is vented from the tank; tank pressures are thereby reduced to about 75 psi. None of the 12 experimentally restarted stages have broken up since 1981.