Preliminary structural evaluation and design of the HL-20

Abstract

A lifting body concept, the HL-20, was designed at NASA Langley Research Center, and a structural analysis of the configuration with a cylindrical pressurized crew cabin was presented. Loads for the vehicle were assembled from mission loading conditions such as abort, on-orbit pressurization, blast overpressure, aerody- namic maneuver, and touchdown. The critical loading conditions were identified, and resultant loads were mapped onto the structure in order to review the effects of the mission loading conditions. The HL-20 structural concept was sized for the mission loads, and the resulting structural weights were calculated. N response to the personnel transport needs of the Space Station Freedom (SSF) and the need for assured manned access to space, candidate Personnel Launch System (PLS) concepts are currently under design and evaluation. The HL- 20, a PLS concept, has been under study at the NASA Langley Research Center for several years. This paper documents the structural design and analysis study of the reference structural concept for the HL-20. The structural analysis was performed using a finite element mod- eling and analysis method. The structural element sizing was performed with a fully stressed design sizing code plus satis- faction of overall buckling criteria. The structural concept is based on a cylindrical pressurized shell that serves as the crew compartment and the main structural load-bearing member. Analysis of a previous structural concept, featuring a pressure shell that conforms to the vehicle exterior shape, is docu- mented in Ref. 1. The present study includes a definition of the structural configuration and identification of the mission loading conditions. The configuration is analyzed for struc- tural integrity when subjected to the mission loading condi- tions. All structural elements are checked for failure due to the loading and are resized, where necessary, in order to obtain a safe structural configuration. The weight of the sized struc- tural configuration is calculated, including a 50% increase for non-optimum considerations, thereby obtaining an analyti- cally derived value as compared to the initial engineering estimate which was based on historical weight data and regres- sion analysis.