Researchers have finally published the results of data recovered from a cracked and singed hard drive that fell to Earth in the debris from the Space Shuttle Columbia, which broke up during reentry on February 1, 2003, killing all seven crew members.
The hard drive contained data from the CVX-2 (Critical Viscosity of Xenon) experiment, designed to study the way xenon gas flows in microgravity. The findings, published this April in the journal Physical Review E, confirmed that when stirred vigorously, xenon exhibits a sudden change in viscosity known as shear thinning. The same effect allows whipped cream and ketchup to go from flowing smoothly like liquids to holding their shapes like solids.
Although the CVX-2 results may not change anyone's life, Robert "Bobby" Berg, the lead investigator for CVX-2 and a physicist at the National Institute of Standards and Technology in Gaithersburg, Md., says the publication caps a 20-year research project that has occupied his thoughts daily since 2003. "It was a load off my shoulders to finally get it published," says the 52-year-old researcher.
The CVX-2 experiment was designed to measure xenon's viscosity close to the critical point, or the combination of temperature and pressure at which liquid and vapor are essentially indistinguishable. Near that point, a gas should "twinkle," Berg says, as droplets quickly condense and evaporate within the thick fog. According to the theory behind shear thinning, as an object swishes through these droplets more vigorously, it should begin slicing through individual droplets and hence feel less resistance.
To test for the effect, the CVX team sent up 0.37 fluid ounces (11 milliliters) of xenon sealed in a vessel that contained a thumbnail-size nickel mesh capable of vibrating at a range of amplitudes [see image]. The group downloaded about 85 percent of the data from the 370-hour experiment while Columbia was in orbit—enough to see that it was working as expected—but the test depended on the full data, which was locked in a nearly 400-megabyte commercial hard drive ensconced in a metal "card cage" and housed with other electronics in a larger vessel in the shuttle's cargo bay.
After the reentry, Berg says, when it was not immediately recovered, "we assumed that it fell out of the cage and burned up and that was it." But engineers from Johnson Space Center had actually found the apparatus in the hanger at Kennedy Space Center where workers had laid out the Columbia debris, says James Myers of the Glenn Research Center in Cleveland, the project's lead engineer.
When the Glenn engineers learned that the hard drive had indeed survived, they sent it to Ontrack Data Recovery in Minneapolis to extract whatever data remained in the cracked hard drive disk [see image]. The data came back about 99 percent complete, but the results were so complex that isolating the shear-thinning effect took an additional several years, Berg says.
He notes that the experiment could have only worked in microgravity, to prevent the xenon from settling under its feather-light weight. With NASA's priorities shifting away from basic research, he says, "this is the sort of experiment that won't be duplicated for a long time, if ever."
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