The National Aeronautics and Space Admin. (NASA, Washington, D.C.) announced on July 2 that it recently completed a major space technology development milestone by successfully testing a large, pressurized cryogenic propellant tank made of composite materials. The composite tank will hold fuel for the next generation of rockets and spacecraft needed for space exploration. Cryogenic propellants, which are gasses chilled to subfreezing temperatures and condensed to form highly combustible liquids, provide the high-energy propulsion solutions critical to future long-term human exploration missions beyond low-Earth orbit. Liquid oxygen and liquid hydrogen have been the traditional cryogenic propellants used to provide the enormous thrust to launch large rockets and Space Shuttles.
In the past, propellant tanks have been fabricated from metals. The almost 8-ft/2.4m diameter composite tank tested at NASA’s Marshall Space Flight Center (Huntsville, Ala.) is considered important because composite tanks could significantly reduce the cost and weight of launch vehicles for other space missions. “These successful tests mark an important milestone on the path to demonstrating the composite cryogenic tanks needed to accomplish our next generation of deep space missions,” says Michael Gazarik, NASA’s associate administrator for space technology. He continues, “This investment in game-changing space technology will help enable NASA’s exploration of deep space while directly benefiting American industrial capability in the manufacturing and use of composites.”
Switching from metallic to composite construction holds the potential to dramatically increase the performance of future space systems through a dramatic reduction in weight. A potential initial target application for the composite technology is an upgrade to the upper stage of NASA’s Space Launch System (SLS) heavy-lift rocket. Built by The Boeing Co. (Chicago, Ill.) at its Tukwila, Wash., facility, the tank arrived at NASA in late 2012. Engineers insulated and inspected the tank then put it through a series of pressurized tests to measure its ability to contain liquid hydrogen at extremely cold temperatures. The tank was cooled to -423°F/-253°C and underwent 20 pressure cycles as engineers increased the pressure to 135 psi.
“This testing experience with the smaller tank is helping us perfect manufacturing and test plans for a much larger tank,” says John Vickers, cryogenic tank project manager at Marshall. “The 18-ft/5.5m tank will be one of the largest composite propellant tanks ever built and will incorporate design features and manufacturing processes applicable to a 27.5-ft/8.4m tank, the size of metal tanks found in today’s large launch vehicles.” The NASA and Boeing team are in the process of manufacturing the tank, which will be tested at Marshall next year. According to Boeing’s cryogenic tank program manager at Marshall, Dan Rivera, the tank manufacturing process represents a number of industry breakthroughs, including automated fiber placement of oven-cured materials, fiber placement of an all-composite, leakproof tank wall design and a tooling approach that eliminates composite tank joints. Such joints, especially bolted ones, have been particularly prone to leaks in the past. Boeing and its partner, Janicki Industries (Sedro-Woolley, Wash.), developed novel tooling to eliminate the need for heavy joints.
“Boeing has experience building large composite structures, and Marshall has the facilities and experience to test large tanks,” explains John Fikes, cryogenic tank deputy project manager at Marshall. “It has been a team effort, with Boeing working with NASA to monitor the tests and gather data to move forward and build even larger, higher performing tanks,” he says.
View a video about cryotank manufacturing and testing here: www.youtube.com/watch?v=IRutJfOsglI