Structural Tests Subject Large Components To Nearly One Million
Pounds Of Force
NASA put the squeeze on a large
rocket test section Tuesday. Results from this structural strength
test at NASA's Marshall Space Flight Center in Huntsville, AL, will
help future heavy-lift launch vehicles weigh less and reduce
development costs.
This project is examining the safety margins needed in the
design of future, large launch vehicle structures. Test results
will be used to develop and validate structural analysis models and
generate new "shell-buckling knockdown factors" -- complex
engineering design standards essential to launch vehicle design.
"This type of research is critical to NASA developing a new
heavy-lift vehicle," said NASA Administrator Charlie Bolden. "The
Authorization Act of 2010 gave us direction to take the nation
beyond low-Earth orbit, but it is the work of our dedicated team of
engineers and researchers that will make future NASA exploration
missions a reality."
The aerospace industry's shell buckling knockdown factors date
back to Apollo-era studies when current materials, manufacturing
processes and high-fidelity computer modeling did not exist. These
new analyses will update essential design factors and calculations
that are a significant performance and safety driver in designing
large structures like the main fuel tank of a future heavy-lift
launch vehicle. During the test, a massive 27.5-foot-diameter and
20-foot-tall aluminum-lithium test cylinder received almost one
million pounds of force until it failed. More than 800 sensors
measured strain and local deformations. In addition, advanced
optical measurement techniques were used to monitor tiny
deformations over the entire outer surface of the test article.
The Shell Buckling Knockdown Factor Project is led by engineers
at NASA's Engineering and Safety Center (NESC), and NASA's Langley
Research Center in Hampton, Va. NASA's heavy-lift space launch
system will be developed and managed at Marshall. "Launch vehicles
are thin walled, cylindrical structures and buckling is one of the
primary failure modes," said Mark Hilburger, a senior research
engineer in the Structural Mechanics and Concepts Branch at Langley
and the principal investigator of the NESC's Shell Buckling
Knockdown Factor project. "Only by studying the fundamental physics
of buckling through careful testing and analysis can we confidently
apply the new knowledge to updated design factors. The outcome will
be safer, lighter, more efficient launch vehicles."
Leading up to this full-scale test, the shell buckling team
tested four, 8-foot-diameter aluminum-lithium cylinders. Current
research suggests applying the new design factors and incorporating
new technology could reduce the weight of large heavy-lift launch
vehicles by as much as 20 percent. "Marshall's Structural and
Dynamics Engineering Test laboratory is uniquely suited for shell
buckling testing," said Mike Roberts, an engineer in Marshall's
structural strength test branch and the center lead for this
activity. "Originally built to test Saturn rocket stages, the
capabilities found here were essential to developing the
lightweight space shuttle external tank flying today and for
testing International Space Station modules."
For this test, Marshall led all test operations including the
engineering, test equipment design and safety assurance. Lockheed
Martin Space Systems Company fabricated the test article at
Marshall's Advance Weld Process Development Facility using
state-of-the-art welding and inspection techniques. Langley
engineers led the design and analysis of the test articles, defined
the test requirements, and developed new optical displacement
measurement standards that enabled highly accurate assessment of
the large-scale test article response during the test.
In the future, the shell buckling team will test carbon-fiber
composite structures that are 20-30 percent lighter than aluminum
and widely used in the automotive and aerospace industries.