[Show abstract][Hide abstract] ABSTRACT: The Long Duration Exposure Facility (LDEF) Experiment AO187-2 consisted of 237 capture cells, 120 on the leading edge and 117 on the trailing edge. Each cell was made of polished Ge plates covered with 2.5 micron thick mylar foil at 200 microns from the Ge. Although all leading edge cells and 105 trailing edge cells had lost their plastic covers during flight, optical and electron microscope examination revealed extended impacts in bare cells from either edge that apparently were produced by high velocity projectiles while the plastic foils were still in place. Detailed optical scanning yielded 53 extended impacts on 100 bare cells from the trailing edge that were selected for SIMS chemical analysis. Lateral multi-element ion probe profiles were obtained on 40 of these impacts. Material that can be attributed to the incoming projectiles was found in all analyzed extended compact features and most seem to be associated with cosmic dust particles. However, LDEF deposits are systematically enriched in the refractory elements Al, Ca, and Ti relative to Mg and Fe when compared to IDP's collected in the stratosphere and to chondritic compositions. These differences are most likely due to elemental fractionation effects during the high velocity impact but real differences between interplanetary particles captured on LDEF and stratospheric IDP's cannot be excluded. Recently we extended our studies to cells from the leading edge and the covered cells from the trailing edge. The 12 covered cells contain 20 extended impact candidates. Ion probe analysis of 3 yielded results similar to those obtained for impacts on the bare cells from the trailing edge. Optical scanning of the bare leading edge cell also reveals many extended impacts (42 on 22 cells scanned to date), demonstrating that the cover foils remained intact at least for some time. However, SIMS analysis showed elements that can reasonably be attributed to micrometeoroids in only 2 out of 11 impacts. Eight impacts have residues dominated by Al and one dominated by Ti, indicating a preponderance of orbital debris in leading edge impacts.
[Show abstract][Hide abstract] ABSTRACT: Results are presented from the post-flight calibration tests for Impact Plasma and Momentum (IPM-P) sensor of the Dust Impact Detection System (Didsy) on Giotto. The IPM-P sensor was covered by three Kapton films with a total thickness of 22.5 microns. About 1000 particles penetrated this cover during the approach of Comet Halley. The results of the calibration tests are applied to the flight data, which show good agreement with other dust experiments on Giotto. The radial flux profiles measured by IPM-P before encounter are presented. The profiles suggest that small particles are swept to the nightside of the nucleus by a lateral breeze.
No preview · Article · Jan 1989 · Advances in Space Research
[Show abstract][Hide abstract] ABSTRACT: Calibration experiments with the impact plasma and momentum detector
DIDSY-IPM flown on the GIOTTO mission were performed at the plasma drag
accelerator in Munich. Silicate particles with masses between
10-9g and 10-6g and speeds between 2 km/s and 12
km/s were shot on the sensor. At constant speed a linear dependency
between the impact charge and the particle mass was found. The DIDSY-IPM
electronics has a nonlinear response to the impact charge. Additionally,
the penetration limit for the three foil protective cover of the sensor
was determined. A penetration limit of 5×10-10g for
silicate particles at 70 km/s was derived.
[Show abstract][Hide abstract] ABSTRACT: The impact plasma and momentum detector (DIDSY-IPM) was the most
sensitive detector among the DIDSY dust impact sensors on board the
"GIOTTO" spacecraft. It was protected by a 3 plastic foil cover which
was supposed to be retracted before the Halley encounter. The IPM data
from Halley encounter in comparison with dust fluxes, derived from the
PIA experiment and in combination with the results from laboratory
experiments, lead to the conclusion that the protective cover of the
IPM-sensor was not released properly before closest approach. This
implies that only the dust flux of particles with masses larger than the
penetration limits for 2 or 3 of the cover foils (m ≥
3×10-10g and 10-9g, respectively) can be
determined. There is evidence that the IPM protective cover was released
shortly before closest approach.
[Show abstract][Hide abstract] ABSTRACT: Dust capture cells on board the LDEF (Long Duration Exposure Facility) satellite were designed to enable the study of the elemental and isotopic composition as well as the size distribution and flux of interplanetary dust particles (IDPs), destructively collected at 500 km altitude over a period of several years. This is a report on simulation experiments of high velocity impacts on the capture cells which have been performed in order to investigate the relationship of the particle's chemical composition before the impact to the composition of the residue on the cell. To that end, both the projectile material and the impact residues have been analyzed with secondary ion mass spectrometry (SIMS). It is found that elemental fractionation occurs during the impact and that the magnitude of fractionation is related to the volatility of the elements.
No preview · Article · Jan 1986 · Advances in Space Research
[Show abstract][Hide abstract] ABSTRACT: It is proposed that considerable care is required to properly interpret either spacecraft in situ data or lunar crater data as well as near-earth data; in the case of the former, complications may arise which may be attributed to secondary lunar ejecta impacts, in the latter, they may result from impacting earth-orbiting debris. Experimental evidence suggests that most impact pits on lunar rocks with pit diameters smaller than 7 micrometers have been generated by lunar secondary ejecta impacts and not by primary meteoroid impacts. It is also found that lunar crater production rates are more accurate when deduced from meteoroid space experiments and not from solar flare track ages. It is concluded that in so far as all of the above qualifications are taken into account, a self-consistent meteoroid flux versus mass distribution is obtained.