Design and fabrication techniques for a large titanium 15-3-3-3 propellant tank

Abstract

THE titanium industry has had only limited success in fabrication and assembly using the titanium alloy 15-33-3. Presented are the results of a program to design, fabricate, assemble, and test a large propulsion tank made from titanium 15-3-3-3. The propulsion tank, 75 in. in diameter and 106 in. in length, contains approximately 15,000 Ib of propellants. The propellants are separated by a common bulkhead designed to be nonpressure-supported and to have no communicating welds to ensure no leakage between the fuel (monomethylhydrazine) and the oxidizer (mixed oxides of nitrogen). The propellant tank is the core structural component of a liquid stage envisioned for spacecraft using the space transportation system (STS) launch vehicle. The fabrication of the tank end domes and common bulkhead presented the greatest challenge. Different fabrication techniques considered for these domes were super plastic forming, closed hot die forging, cold spin forming, and explosion forming. Subscale pilot programs were conducted for explosion forming and spinning. A hot spinning operation was selected as the fabrication technique. This program has advanced the stateof-the-art and use of the titanium 15-3-3-3 alloy. The successful completion of the structural tests demonstrated structural adequacy and confirmed that titanium 15-3-3-3 could be used for large propulsion tank structures.