Development of Impact Ionization Dust Counter for the Space

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PLANET-B is an ISAS spacecraft which will investigate the upper atmosphere and the surroundings of Mars between 1999 and 2001. To clarify the presence and characteristics of the Martian dust ring/torus, an impact ionization dust detector will be on board PLANET-B.The detector (PLANET-B Mars Dust Counter), which is an improved version of the Munich Dust Counters of HITEN and BREMSAT,is developed at Technology University of Munchen under the corporation between Japanese and Germany group.MDC weighs only 690g with an aperture area 140cm^2. The detectable mass range will be between 10^<-16>g and more than 10^<-6>g and the velocity range will be from 1km/s to more than 70km/s. Since PLANET-B executes retrograde elliptic orbits close to the zodiacal plane, our detector can investigate the spatial distribution of prograde dust particles from Phobos and Deimos with relative encounter velocity as large as or higher than 1km/s. PLANET-B MDC shall also measure the dust environment around the Earth and interplanetary and possibly interstellar dust particles.Between 1994-1996, our members (Sasaki, Ohashi, Nogami, and Ishimoto) visit Germany for discussion of basic design of proto-and flight models of MDC,manufacturing of models, calibration tests using the ultra-high velocity dust accelerator. New MDC has several advantages over HITEN-MDC : larger aperture, cut of solar illumination, and three channels.