A team of engineers from Northrop Grumman and NASA’s Marshall Space Flight Center have demonstrated that a new, specially designed fuel tank made from composite materials can safely hold and contain liquid hydrogen under simulated launch conditions.
The tests were conducted on November 22 at the Marshall Center, as part of NASA’s Next Generation Launch Technology (NGLT) program, an ongoing effort to develop and mature technologies required for a ‘next generation reusable launch vehicle’.
According to a Northrop Grumman, liquid hydrogen is an essential but highly volatile fuel used in the combustion process that propels rockets. It must be stored and used at -423 degrees Fahrenheit, a temperature that causes most materials to become quite brittle. Liquid hydrogen also has an extremely fine molecular structure, which allows it to seep through the tiniest of holes.
‘This test represents a significant step forward in reducing the risks associated with using composite tanks to store cryogenic fuels,’ said Joan Funk, NASA’s NGLT cryogenic tanks project leader. ‘Composite tanks offer a 10 to 25 percent reduction in weight over current aluminium tanks, so their use would allow us to consider larger payloads. They could also help us reduce costs associated with acquiring and operating a reusable launch vehicle.’
For the tests, the Northrop Grumman/NASA team filled a 6-foot diameter x 15-foot long tank with liquid hydrogen, then subjected it to an axial load and an internal pressure of approximately 120 pounds per square inch to simulate the stresses experienced by a rocket during launch. The tank is approximately one quarter of the projected size (27.5 feet in diameter x 80 feet long) of a fuel tank required for some reusable launch vehicle concepts. An axial load is a load applied along the vertical axis of the launch vehicle.
During the next nine months, the team will fill, apply internal and external loads, and drain the tank approximately 40 times to demonstrate its structural integrity at cryogenic temperatures and its ability to be reused.
According to Tod Palm, Northrop’s composite tank project leader, the team’s success resulted from three technical advances: a new approach to fabricating the walls of the tank; the use of a secondary barrier film to prevent liquid hydrogen from seeping into the tank walls; and a perforated honeycomb core design that ensures crew safety by venting liquid hydrogen to space in the event that any of the fuel seeps past the barrier film.
Northrop Grumman’s work for NASA on the cryogenic fuel tanks is being done under a 3-year series of Next Generation Launch Technology contract options that began in June 2001.
The contracts, collectively worth approximately $30 million, include work on permeation resistant composite cryotanks, development and refinement of new manufacturing processes that will allow the company to build large composite tanks without an autoclave; and design and engineering development of conformal fuel tanks appropriate for use on a single-stage-to-orbit vehicle.