Discovery A Testbed For Future Spacecraft
Jan 26, 2009
Frank Morring, Jr. morring@aviationweek.com
NASA managers plan to use the space shuttle Discovery as a testbed during the up STS-119/15A mission, using the unique capabilities of the shuttle flight envelope to gather data that NASA's Constellation Program will use to design the vehicles that will succeed the shuttle fleet after the three orbiters are retired by the end of next year.
As was the case on the most recent shuttle mission, pressure transducers in the four-segment solid-fuel rocket motors that boost the shuttle stack off the launch pad will collect data on the thrust oscillation phenomenon that is driving the design of the Ares I crew launch vehicle.
Like all solid-fuel rockets, the shuttle boosters produce vibrations as they near burnout. Calculations show that vibrations from the five-segment version of the shuttle boosters baselined as the Ares I first stage will travel through the stack into the Orion crew exploration vehicle atop it at levels that could hamper crew performance.
Shuttle Program Manager John Shannon says the crew seats in Discovery also will be instrumented to measure how much vibration from the solid-fuel boosters actually reaches the crew during ascent.
"We have returned to using the space shuttle as a research vehicle, and we're trying to learn more and more about spaceflight and hypersonic reentry and the dynamics of ascent," he says.
Discovery's flight also will mark the beginning of a series of experiments in the aero-thermodynamics of hypersonic reentry that probably will continue as long as Discovery flies. Known as the "boundary layer detailed test objective," the test involves a special ceramic tile on the bottom of the orbiter's left wing that has a 0.25-inch bump molded into it. Technicians have installed nine thermocouples aft of the bump to measure temperature at different points downstream in the aerodynamic flow.
"What we expect to have happen is we will take that boundary layer from laminar to turbulent flow at a higher velocity than we typically would if we didn't have a bump," Shannon says. "This adds to our understanding of how flow transitions from laminar to turbulent flow and what kind of heating rate you can have from this."
The tests, in an area of thick tiles with a lot of thermal margin, should produce data "in a real flight environment" that the Constellation Program can use to develop materials and coatings for the thermal protection system on the Orion crew exploration vehicle, he says.
Photo of Discovery: NASA
