2344. Space Shuttle External Tank Performance Enhancements

Paper

Abstract

For over 20 years, Lockheed Martin Manned Space Systems, under contract from NASA’s Marshall Space Flight Center (MSFC), has supported the Space Shuttle Program as the exclusive supplier of External Tanks (ETs). Beginning in 1973 with the original Standard Weight Tank (SWT) used on the first six Shuttle launches and continuing with the Lightweight Tank (LWT) in use today, the ET has achieved 100% mission success on over 70 Space Shuttle missions. Now, Lockheed Martin has been contracted by NASA to develop a new, even lighter version of the ET, called the Super Lightweight Tank (SLWT), to provide over half of the additional payload capability required for the Space Shuttle to support launch and maintenance of the International Space Station. One hundred and fifty-eight feet long and 28 feet in diameter, the ET delivers the 230,000 pounds of liquid hydrogen (LH2) and 1.38 million pounds of liquid oxygen (LO2) required by the Space Shuttle Main Engines (SSMEs) during the Shuttle’s eight and one-half minutes of powered flight. In addition, as the primary structural backbone of the Shuttle launch vehicle, the ET effectively and efficiently distributes over 4 million pounds of thrust generated by the SSMEs and the Solid Rocket Boosters (SRBs) during launch. The ET consists of three primary structural components: a 145,000 gallon LO2 tank, a 390,000 gallon LH2 tank and an Intertank (an unpressurized cylindrical structure used to join the LO2 and LH2 tanks into one contiguous structure and serve as the primary SRB attachment point). The main structural components of the current LWT are fabricated primarily from 2219 aluminum alloy and over 3000 feet of welds are used during the assembly of the primary structural elements. Once assembled, the ET is covered with Thermal Protection System (TPS) materials to maintain the LH2 and LO2 propellants at their optimum use temperatures of -423?F and -293?F respectively prior to and during launch for propellant conditioning, to minimize the formation of ice on the ET prior to launch and to protect the ET structure from the aerodynamic environment encountered during ascent.