Dynamic Probabilistic Analysis of Bolt Retraction During Separation of the Propulsion Stage of an Orbiting Vehicle

Abstract

The Crew Return Vehicle (CRV) lifting body is designed to separate from its De-Orbit Propulsion Stage (DPS) prior to re-entry into the earthOs atmosphere. The DPS is separated from the CRV by six exploding nuts each attached to a spring-loaded retracting bolt. The design calls for the bolts to retract across the separation plane without a bolt hang-up which appears unlikely, yet of concern. A probabilistic analysis is performed to identify design variables that most affect the probability of hang-up. The most dominant variables are the gap distance between the CRV clearance hole and the retraction bolt, and the effect of strain energy to kinetic energy conversion. The most readily changed design variable is the gap distance. The conclusion of the analysis is that the retraction system has a probability of hang-up of less than 0.0003. Although remote, the probability of bolt hangup can be substantially reduced by enlarging the bolt clearance dimension on the CRV side of the system. By increasing the gap dimension on the CRV side from 37 to 60 thousandths of an inch, the probability of bolt hang-up will become eight orders of magnitude smaller for the non-axial bolt model and three orders of magnitude smaller for the thermal shifting model.