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Projects: Stardust@homeHow to Steady a Vibrating Armby Amir Aelxander
As dusters from around the world continue to search for interstellar dust particles in aerogel movies, the Stardust@home team in Berkeley is preparing for the next stage: extracting the particle candidates from the collector and making them available to scientists. Doing so requires cutting out tiny segments from the aerogel collector, which contain the possible traces of interstellar dust particles collected by the spacecraft Stardust during its 7-year long journey. Extracting these aerogel segments is a remarkably delicate task, requiring the utmost precision. Under the eye of a microscope and controlled by a micromanipulator, an ultra-fine glass needle cuts slowly and repeatedly into the aerogel tile, until a “keystone” is extracted. An ultra-thin section of the keystone, which contains the candidate particle, is referred to as a “pico-keystone.” In early October team member Zack Gainsforth traveled down to the Johnson Space Center (JSC) in Houston to try out the method. In order to avoid endangering any actual samples collected in space, Zack left the Stardust collector itself alone. Instead he conducted the trials on a flight spare tray, identical in all respects to the real collector except for the fact that it stayed on Earth when its twin flew in space. Zack’s trials at JSC demonstrated that pico-keystones can be extracted effectively with the method developed by Westphal and the team. But they also pointed to a persistent and nagging problem: the long steel arm holding the needle tended to vibrate, which made it impossible to achieve the level of accuracy required for the task. This set off an intense month of brain-storming back in Berkeley, where the team experimented with all manner of solutions to the problem. Proposed remedies ranged from trying a different material for the arm to installing new software on the micromanipulator that controls the needle’s movements. In early November Westphal and team member Dave Frank flew once more down to Houston to try out their solutions.
By the end of their stay the problem was solved to their complete satisfaction. It turned out that the most effective ways for avoiding the vibrations were also the most obvious ones. The entire extraction assembly, including the microscope, tray, micromanipulators, arms and needles, was mounted on a vibration isolation table. This insulated the entire apparatus from external factors such as passing planes or nearby trucks. In addition, Westphal and Frank installed new software that drastically slowed down the needle’s motion. This cut back on the vibrations generated by the needle itself. Together, these two relatively simple adjustments seemed to resolve the problem, and there was no need to resort to more radical remedies.
The Stardust@home team is now confident that they can begin extracting actual dust candidates in the near future. If all goes well they expect to be back at JSC before the end of the year, once again cutting pico-keystones out of an aerogel tray. This time, however, the work will be done not on an innocuous flight spare, but on the true aerogel collector, returned from a journey of 7 billion miles. Somewhere within it they hope to find those precious interstellar dust particles, forged in the cores of distant Suns, and carrying with them some of the most guarded secrets of the universe.
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