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| Cometary and Interstellar Dust Analyzer Instrument
The Cometary and Interstellar Dust Analyzer instrument intercepts dust and performs real-time compositional analysis for transmission back to Earth. The Stardust dust analyzer is the same instrument design that flew on Giotto and two Vega spacecraft, where it obtained unusual data on the chemical composition of individual particulates in Halley's comet. The instrument is located on the underside of the Stardust spacecraft.
The dust analyzer is a mass spectrometer, which determines the size of ions by comparing differences in their flight times. The instrument operates relatively simply. When a dust particle hits the target of the instrument, an electrostatic grid extracts ions from it. Depending on the polarity of the target grid, positive or negative ions can be extracted from the dust. The extracted ions move through the instrument, are bounced off a reflector, then read by a detector. Heavier ions take more time to travel through the instrument than lighter ones, so the flight times of the ions are used to calculate their mass.
Image above: Stardust's Cometary and Interstellar Dust Analyzer. Image credit: NASA/JPL.
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Technical Details
The instrument consists of an inlet, target, ion extractor, time-of-flight mass spectrometer and ion detector. The inlet is baffled to prevent sunlight from entering and raising the background noise in the detector. The target was planned to be a corrugated Ag or other heavy metal material. It was not necessary to have a moving Ag foil for the Wild 2 flyby, as was done for the higher flux at Halley. The target area was increased to 50 cm2 from the Halley Mission instrument's 5 cm2 target.
During its operation, a light flash, which accompanies the dust impact on the target, is detected and used to set the zero for the time-of-flight measurement. Electrostatic grids extract ions, depending from the impact microplasma. These ions move down a bent-tube time-of-flight mass spectrometer, with an electrostatic reflector to focus ions of similar energies onto the ion detector. By measuring their arrival time, the mass of the ions can be determined. It is expected that at the 6.1 km/s flyby speed, molecular ions as well as atomic ions will be important in the observations. The instrument is sensitive at least over the range AMU=1 to 150, though sub-micron sized particles produce observable signals and compositional profiles too.
The use of a recorder mode allow a superior data set to be collected than was possible from the data-constrained links that were available during previous PIA flights. Most of this data will be played back slowly over ensuing days or weeks after the comet flyby.
The co-investigator in charge of the Cometary and Interstellar Dust Analyzer is Jochen Kissel of MPE, the Max-Planck-Institut f. Aeronomie in Lindau, Finland. The instrument has been developed and built by von Hoerner & Sulger GmbH in Schwetzingen, Germany, in close cooperation with the MPE under contract by the DARA, Deutsche Agentur f|r Raumfahrtangelegenheiten, Bonn. Software for the Cometary and Interstellar Dust Analyzer instrument is being developed by The Finnish Meterological Institute, Helsinki.
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