Albrecht Glasmachers

Comet 67P/Churyumov–Gerasimenko: Close-up on Dust Particle Fragments

The COmetary Secondary Ion Mass Analyser instrument on board ESAs Rosetta mission has collected dust particles in the coma of comet 67P/Churyumov-Gerasimenko. During the early-orbit phase of the Rosetta mission, particles and particle agglomerates have been imaged and analyzed in the inner coma at distances between 100 km and 10 km off the cometary nucleus and at more than 3 AU from the Sun. We identified 585 particles of more than 14 μm in size. The particles are collected at low impact speeds and constitute a sample of the dust particles in the inner coma impacting and fragmenting on the targets. The sizes of the particles range from 14 μm up to sub-millimeter sizes and the differential dust flux size distribution is fitted with a power law exponent of -3.1. After impact, the larger particles tend to stick together, spread out or consist of single or a group of clumps, and the flocculent morphology of the fragmented particles is revealed. The elemental composition of the dust particles is heterogeneous and the particles could contain typical silicates like olivine and pyroxenes, as well as iron sulfides. The sodium to iron elemental ratio is enriched with regard to abundances in CI carbonaceous chondrites by a factor from ˜1.5 to ˜15. No clear evidence for organic matter has been identified. The composition and morphology of the collected dust particles appear to be similar to that of interplanetary dust particles.

High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko

The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley. Such matter is generally thought to have originated in the interstellar medium, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization. Many gaseous organic molecules, however, have been observed; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.

Mars Dust Counter

In order to unveil the presence and characteristics of Martian dust ring/torus, Mars Dust Counter (MDC) is aboard ISAS’s spacecraft PLANET-B, which will be launched in 1998 summer and investigate the upper atmosphere and surrounding environment of Mars between 1999 and 2001. MDC PLANET-B is an improved version of impact-ionization dust detectors aboard HITEN and BREMSAT. It weighs only 730 g with the sensor aperture area of 140 cm2. To improve signal to noise ratios and to precisely determine the risetime of signals, a neutral target channel is added independent of ion and electron target channels. Detectable velocity (v) range is between 1 km/s and more than 70 km/s, which will cover all possible dust clans: circummartian (low v), interplanetary (mid v), and interstellar (high v) particles. Measurable mass range is 5 × 10−15 and 10−10 g at v = 10 km/s. Since PLANET-B takes an elliptic retrograde orbit around Mars, MDC can investigate particles from Phobos and Deimos with relative velocity higher than 1 km/s. Therefore, MDC can clarify the presence of a confined dust ring along Phobos’ orbit and an extended dust torus along Deimos’ orbit, and it may answer whether these ring and torus are self-sustained or not. Since the nominal operation of PLANET-B is longer than one Martian year, MDC may detect predicted seasonal variation of the ring/torus structure.

The Munich Dust Counter --- A Cosmic Dust Experiment on Board of the MUSES--A Mission of Japan

The Munich Dust Counter (MDC) is a scientific experiment on board of the MUSES-A mission of Japan. It is the result of a cooperation between the Institute of Space and Astronautical Science (ISAS) of Japan and the Chair of Astronautics of the Technische Universitat Munchen (TUM) of Germany. The MDC is an impact ionization detector designed to determine mass and velocity of cosmic dust. Here a short overview over the MUSES-A mission is given to show the measurement situation of the MDC experiment. The measurement principle of the instrument together with a discussion of the scientific objectives and the design of the experiment is summarized.

The Present Status of the Munich Dust Counter Experiment on Board of the Hiten Spacecraft

The Munich Dust Counter (MDC) is a scientific experiment on board the MUSES-A mission of Japan measuring cosmic dust. The satellite HITEN of this mission has been launched on January 24th, 1990 from Kago-shima Space Center. Here the present status of the MDC experiment is summarized. The number of dust particles measured so far is presented together with first and preliminary results of flux calculations and spatial as well as directional distributions of cosmic dust particles measured until July 25, 1990. A clear evidence of particles coming from the inner solar system (beta-meteoroids) already has been found. These are compared to particles coming from the apex direction.

Multistop-Zeitmeßsystem mit kleiner Totzeit für Weltraum-Anwendungen

This paper discusses principles of multistop time measuring systems as well as adequate interpolation techniques for improved resolution. For the time measuring system of a space born mass spectrometer a digital interpolation channel using a tapped delay line with data-flipflops as sampling elements is presented, which gives a resolution of <1 ns and a dead time <3 ns

Messungen charakteristischer Werte von Signalen

Zur Erfassung aller in einem Signalzeitverlauf moglichen Signifikanzen mus der gesamte Zeitverlauf der Signalfunktion verfolgt werden. Die dazu moglichen Verfahren und Messysteme sind in Kap. 6 behandelt. Haufig sind jedoch nur ein oder wenige Signalparameter als Informationstrager signifikant. Es lohnt sich deshalb in solchen Fallen nicht, den in Kap. 6 beschriebenen mestechnischen Aufwand zu treiben.

Komponenten von Meßschaltungen

Eine exakte und allgemein anerkannte Definition und Eingrenzung des Begriffes “Operationsverstarker” gibt es nicht. Ursprunglich wurden “operational amplifiers” (= Operationsverstarker, OP) als Verstarkergrundelemente in Analogrechnern eingesetzt, wo mit ihrer Hilfe mathematische Operationen durchgefuhrt wurden. Das wichtigste Kennzeichen eines (idealen) Operationsverstarkers ist, das die Eigenschaften des mit ihm realisierten (Rechen-) Verstarkers nur durch die ausere Be-schaltung bestimmt werden. Ein idealer OP ist eine spannungsgesteuerte Spannungsquelle mit der Leerlaufspannungsverstarkung v0 →∞.

Darstellung von Signalzeitverläufen

Der Informationsinhalt elektrischer Signale liegt in deren Signalgrose und Zeitverhalten. Unter dem Begriff der “Signalgrose” versteht man im allgemeinen seine Polaritat und seine Amplitude. Das “Zeitverhalten” wird ublicherweise bei periodischen Signalen durch die Wiederholfrequenz oder Periodendauer und bei im-pulsformigen Signalen durch den Zeitpunkt des Auftretens des Signals in Bezug auf einen Referenzzeitpunkt sowie durch die Signalanstiegszeit (10 % ... 90 % der Amplitude) und die Signalhalbwertsbreite FWHM (Full Width at Half Maximum) angegeben. In vielen Fallen ist nur eines der o. g. Kriterien signifikant. In jedem Fall aber erfast man alle moglichen signifikanten Informationskriterien eines Signals, wenn man seinen vollstandigen Signal-Zeitverlauf darstellt bzw. registriert.

Digital/Analog- und Analog/Digital-Umsetzer

Analog/Digital- und Digital/Analog-Umsetzer stellen in einer Meskette die Bindeglieder zwischen den meist analogen Sensoren bzw. Aktoren und der digitalen Signalverarbeitungseinheit (s. Bild 1.1) dar. Bedingt durch die unterschiedlichen Anforderungen an Bandbreite, Amplitudendynamik und Genauigkeit existiert eine so grose Vielzahl an Umsetzungsverfahren und -Schaltungen, das eine vollstandige Behandlung den Rahmen dieses Buches sprengen wurde. Deshalb sollen hier nur aus schaltungstechnischer Sicht einige grundlegende Prinzipien aufgezeigt werden, die bei Umsetzern fur mestechnische Anwendungen von Bedeutung sind.