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A cosmic dust monitor for use onboard a spacecraft is currently being developed using a piezoelectric lead zirconate titanate element (PZT). Its characteristics of the PZT sensor is studied by ground-based laboratory impact experiments using hypervelocity particles supplied by a Van de Graaff accelerator. The output signals obtained from the sensor just after the impact appeared to have a waveform that was explicitly related to the particle’s impact velocity. For velocities less than ∼6 km/s, the signal showed an oscillation pattern and the amplitude was proportional to the momentum of the impacting particle. For higher velocities, the signal gradually changed to a single waveform. The rise time of this single waveform was proportional to the particle’s velocity for velocities above ∼6 km/s. The present paper reports on results for the low velocity case and especially discusses the effect of an outer coating of the sensor with a paint, which is used to reduce heating by solar radiation.

A cosmic dust detector is currently being developed using a piezoelectric lead zirconate titanate (PZT) element. The characteristics of the multilayered detector (MD), which was composed of one hundred PZT disks, were investigated by bombarding it with hypervelocity iron particles supplied by a Van de Graaff accelerator. It was confirmed that there was a linear relationship between the signal amplitude observed from MD and the momentum of the particles. As compared with the single-layered detector (SD) that was composed of one PZT disk, it was found that the sensitivity of MD was ∼3 times higher than that of SD within the limits of the experimental conditions.

The detector characteristics of a pentagonal element were studied by colliding it with hypervelocity micro-particles. A charge-sensitive amplifier was developed for the element of its capacitance ∼10 nF. The output amplitudes were expressed as a linear function of the momentum at collision. Empirical formulas obtained from on-ground experiments could be used for the calibration of the detector. The pentagonal element was potential to measure the momentum during collision from the output amplitude. A set of electrodes on the surface was used to confirm the measurement of the coordinates at collision. A possible application of this pentagonal element on a real-time dust detector was discussed.

Mars Dust Counter (MDC) is a light-weight dust detector of impact ionization type on board Japanese Mars mission NOZOMI. NOZOMI was launched on July 4th (3rd at UT) 1998. From December 1998 to December 2003 for five years, NOZOMI took eccentric orbits between the Earth’s and Mars’ orbits. Until April 2002, MDC continuously observed interplanetary dust. MDC has detected nearly 100 doubtless dust impacts. There were observed several high-velocity particles, which are apparently different from Keplerian dust particles gravitationally bound to the sun. Directional analysis showed that MDC has detected several particles of interstellar origin during the cruising phase of NOZOMI.

著者人数: 14名, 資料番号: SA1003696000

著者人数: 18名, 資料番号: SA1003695000

The Mars Dust Counter (MDC) is an impact-ionization dust detector on board the Japanese Mars mission NOZOMI, which was launched on 1998-07-04. It is an improved type of MDC-HITEN and MDC-BREMSAT and has three detection channels (electron, iron, and neutral) to discriminate noise signals from impact signals. The main aim of the MDC is to measure dust particles around Mars and reveal the distribution of the predicted Martian ring or torus of dust from Phobos and Deimos. On 1998-07-13, the MDC detected the first impact signal. On 1998-11-18, NOZOMI encountered the Leonids meteoroid stream. The MDC detected two dust impacts, but directional analysis showed that those particles probably did not belong to the Leonids. The NOZOMI orbital plan was changed; Mars insertion was postponed to be on 2004-01-01. By the end of 1999, MDC had detected more than 40 particles, including at least three — maybe five - particles of interstellar origin. Between 1999 and 2003, MDC-NOZOMI can thus continuously measure interplanetary dust.