Tests Boosts Confidence in Using Composite Tanks for Reusable
A team of engineers
from Northrop Grumman Corporation and NASA's Marshall Space Flight
Center, Huntsville (AL) 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 Nov. 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. 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 aluminum 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
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
"This test exemplifies the technological leadership that
Northrop Grumman is bringing to the challenge of achieving
affordable, reusable access to space," said Tod Palm, Northrop
Grumman's composite tank project leader. "The team's
breakthrough in fabricating cryogenic fuel tanks has significant,
long-term implications for the nation's civil and military space
programs." According to Palm, 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 an innovative,
perforated honeycomb core design that ensures crew safety by safely
venting liquid hydrogen to space in the unlikely 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.