The second single-piece 5.5 meter diameter full-scale spun form dome was manufactured from a flat plate "blank" made from two pieces of aluminum lithium 2195 plate, which had been friction stir welded together. (Credit: MT Aerospace)

Five years ago, NASA engineers at the Marshall Space Flight Center in Huntsville, Ala., and Langley Research Center in Hampton, Va., decided to manufacture a 5-m diameter fuel tank fabricated entirely from aluminum lithium 2195 alloy. They used various manufacturing techniques, including friction stir welded joints and single-piece spun formed domes.

Recently, the second single-piece, 5.5-meter diameter full-scale spun form dome was manufactured from a flat plate blank made of two pieces of Al-Li 2195, friction-stir welded together.

Another full-scale development tank dome is scheduled to be built and tested in the coming months, as part of the joint, four-year technology demonstration program.

What’s significant about this advance in manufacturing tank domes? This technology incorporates lighter weight material, reduces significantly the number of pieces needed to create a tank dome, eliminates numerous complex welding, machining and inspection steps, and can be used on any large liquid propellant tank with greater reliability and lower costs.

To manufacture a typical dome using aluminum alloy 2219 requires eight gore panels, or pie-shaped pieces, 10 welding steps, and multiple operations and inspections to assemble into a full-scale tank dome.

The new technique takes two commercial, off-the-shelf aluminum lithium 2195 plates that are joined by friction stir welding to produce a sufficiently large starting blank. Then, the welded plate blank is “spun formed” to create the single-piece tank dome.

This approach allows engineers and technicians to use the lighter-weight, higher-strength alloy — aluminum lithium 2195 — compared to current tank designs, which use the heavier, lower-strength aluminum 2219 alloy. This could reduce the weight of future liquid propellant tank domes by 25 percent, both through the material replacement and the reduction in the number of welds.

NASA's Marshall Space Flight Center and Langley Research Center partnered with Lockheed Martin Space Systems and MT Aerospace to advance dome manufacturing by making use of existing commercial materials and cutting edge technology.

This partnership demonstrates NASA’s desire to access new ideas and innovations to address technical challenges that will benefit NASA and next-generation space exploration.

Engineers at Langley and Marshall are currently evaluating samples of the successfully manufactured tank dome to ensure the strength and reliability of these tank-forming processes.