Flight of Discovery (Continued)

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Engineers determined they had to completely avoid using insulation on the bipod or any other area that protruded from the ET. Instead, they cleverly redesigned the fittings and other suspect components with electric heaters that keep the non-insulated metal component warm enough—up to 250 degrees Fahrenheit—to discourage ice buildup. And without foam insulation or ice, the probability of debris impacting the Orbiter is significantly reduced.

Even with all the ET design changes, the possibility of debris impacts, while drastically reduced, cannot be completely eliminated. The danger of triggering foam breakage is most pronounced roughly two minutes after launch, when the Shuttle is subject to the greatest aerodynamic forces. Using SGI® Altix® servers and Silicon Graphics Fuel® desktop visualization systems, NASA engineers analyzed the new ET's behavior by subjecting it to virtual air flows at the critical peak aerodynamic conditions. The simulations help engineers understand the details of the air velocities, densities, and pressures that the Shuttle system faces as it accelerates out of the Earth's atmosphere.

The detailed simulations revealed that, at peak aerodynamic conditions when the Shuttle is soaring at roughly two to three times the speed of sound, lightweight foam debris traveling just 40 or 50 feet can inflict serious damage to the Orbiter wing. The danger comes not from the size or the weight of the foam, but from the relative velocity that it attains due to the airflow before it strikes the wing. It's no wonder NASA engineers analyzed and reanalyzed the new tank design to minimize the chance of debris coming loose.

'The best information'

Leveraging NASA's 10,240-processor SGI Altix system, named Columbia to honor the lost crew, and a local 64-processor SGI Altix system, engineers conducted numerous detailed debris trajectory analyses, studying literally billions of possible debris trajectories. Using NASA's Cart3D software, analysts simulate the unsteady, tumbling flight of various sizes and shapes of debris, all with an eye toward avoiding critical damage to the Orbiter wing's RCC panels or its undercarriage heat shield formed by more than 20,000 black ceramic tiles.

While ET modifications reduce the risk of debris damage, they cannot eliminate it. Damage to the Shuttle is always a possibility: Following earlier flights, engineers observed an average of about 100 detectable debris impacts to the Shuttle's surface. The damage is caused by multiple sources, such foam shed from the ET during ascent and gravel kicked up by the Orbiter's tires during landing. But only on Columbia was the harm severe enough to impact the safety of the mission.

Still, NASA is determined to avoid further accidents. For the first time ever, crew members can conduct in-flight repairs on the Shuttle's heat shield. To determine whether repairs are warranted, the crew will use cameras and lasers to examine and measure any damage sites on the RCC wing panels and the ceramic tiles on the undercarriage. To gauge the seriousness of any observed damage, a team of NASA aerospace engineers will assess the damage sites, compare them against historical engineering data and, if necessary, run complex computational fluid dynamics (CFD) calculations on the Columbia supercomputer to predict changes in heating due to the damage. These CFD studies will help NASA determine the best strategy for dealing with specific damage cases. They also will be useful in evaluating ahead of time the effectiveness of any on-orbit repairs deemed necessary.

NASA engineers have already tested this CFD-based aerothermal analysis process. The tests have demonstrated that in less than 24 hours, engineers can complete 100 different CFD real-gas Navier-Stokes calculations, each involving 10 million grid points and 10,000 iterations. This feat was accomplished using fewer than half of the Columbia supercomputer's 10,240 processors for the dry run. If actual heat shield damage is observed during Discovery's upcoming flight, the Shuttle crew will have the support of NASA's talented and dedicated damage assessment teams—not to mention all of Columbia's computational capacity.

"This Return to Flight effort, and the collaboration between so many NASA centers, is a clear reflection of the agency's unrelenting spirit of discovery and innovation," says Bob Bishop, chairman and CEO of SGI. "SGI is delighted to see America take flight again, and we're proud to lend a hand."

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Using SGI technology for Return to Flight

Marshall Space Flight Center
Using SGI visualization and server systems, Marshall engineers are designing a heating unit to be installed on the expansion joints of the shuttle's liquid oxygen line. The heating unit's design hinders the buildup of ice during launch. Marshall scientists also are analyzing the shuttle's propulsion systems on these systems.

Michoud Assembly Facility
This government-owned component of Marshall Space Flight Center is using SGI technology to complete impact analysis simulations of foam, ice, and other debris and to model/analyze the design of the shuttle's external tank.

Kennedy Space Center
Kennedy's Ice/Debris Facility, where NASA gets its first close-up look at launch films, uses a highly advanced SGI imaging system that allows engineers to analyze launch footage, frame by frame, in resolution that exceeds HD quality. NASA recently upgraded the lab's display system, enhancing its ability to assess the effects of debris on the shuttle vehicle in their decision support center for future flights.

Johnson Space Center
Engineers at Johnson used SGI servers to run sophisticated fluid dynamics calculations as part of their effort to assess the bipod closeout redesign, a piece of hardware that attaches the shuttle's external fuel tank to the orbiter during liftoff. Results from these simulations are key inputs for the NASA-developed debris trajectory prediction codes.

Ames Research Center
A full range of SGI technologies, including NASA's Columbia supercomputer, comprised of 10,240 Intel® Itanium® 2 processors, are being used to support several of the agency's Return to Flight activities. These activities include: investigation and analyses of cracks in the main propulsion system's fuel line; aerodynamics studies of the shuttle's ascent; debris transport analyses; development of an automated plotting tool for debris paths; and internal and external aerothermal fluid dynamics studies. The Columbia system is a vital resource for Return to Flight activities underway throughout NASA.

Image credits:
Lockheed Martin/NASA Michoud