SRI International Applies Expertise to Ensure Smooth Space Shuttle Lift-Off
Fracture Physics Researchers Study Kinetics of Explosive Nut Fracture and Stud Release
MENLO PARK, Calif., March 2, 2006 - SRI International, an independent nonprofit research and development organization, today announced that researchers in its Center for Fracture Physics are working with National Aeronautics and Space Administration (NASA) engineers to ensure a smooth lift-off of the five million-pound Space Shuttle from its mobile launch platform.
When the Space Shuttle is launched, each of the eight studs that attach the solid rocket boosters to the mobile launch platform must be released in a fraction of a second. Rapid release is accomplished by explosively fracturing the nuts that hold the studs in place. Large-scale, highly instrumented tests are being performed by NASA at the Kennedy Space Center in Florida and the Marshall Space Flight Center in Alabama. An SRI team of scientists and engineers is applying its expertise in fracture physics to help analyze the test results and determine how quickly the explosive nuts fracture and disengage the studs.
“Each nut has two explosive charges, and problems can occur if the time between detonations exceeds several hundred microseconds,” said Don Shockey, Ph.D, Director, SRI’s Center for Fracture Physics. “Along with NASA engineers, the SRI team is analyzing timing variations and the effects on nut failure and stud release behavior. Some of the answers are being found by examining the nut failure surfaces, the nut fragments, and the markings on the studs after the tests. Other answers are sought by performing computational simulations.”
The SRI team is conducting high-rate fracture experiments on a nickel-based super alloy, the material from which the stud and nut are fabricated. The resulting data are used to develop material models for finite element calculations of explosive nut failure. The researchers then perform computations to simulate the NASA stud release experiments. These computations are the only way to determine certain important details of the explosive nut fracture, because the fracture occurs within the blast containers and cannot be observed.
Factors under investigation include stress wave propagation when the explosive is detonated and how the explosive fractures the nut; how the nut halves disengage from the stud and how details of the release affect the stud motion; and finally, how the nut halves rebound from the blast container and recontact the stud. Agreement with the strain gauge records and high-speed photography from the NASA tests verify the computations.
About SRI International
Silicon Valley-based SRI International (www.sri.com) is one of the world's leading independent research and technology development organizations. Founded as Stanford Research institute in 1946, SRI has been meeting the strategic needs of clients for 60 years. The nonprofit research institute performs contract research and development for government agencies, commercial businesses and private foundations. In addition to conducting contract R&D, SRI licenses its technologies, forms strategic partnerships and creates spin-off companies.
