Thermal histories of the samples of two KOSI comet nucleus simulation experiments

Temperatures recorded during two KOSI comet nucleus simulation experiments strongly suggest that heat transport by vapor flow into the interior of the sample is very important. Two comet nucleus simulation experiments have been done by the KOSI team in a big space simulator. The thermal evolution of the sample during insolation and the results of simplified thermal evolution calculations are discussed. The observed thermal histories cannot be explained by a simple model with heat transferred by heat conduction at a constant conductivity, so a coupled heat and mass transfer problem was considered. The porous ice matrix was assumed to have a constant thermal conductivity and to be in thermal equilibrium with vapor in the pores, the internal pressure being the vapor pressure. The vapor was modelled as an ideal gas because, at the temperatures relevant to the problem, the mean free path length of the vapor molecules is large in comparison with the pore dimensions. The heat capacity at constant volume per unit mass of the two phase mixture was also assumed constant. The vapor was allowed to flow and transfer heat in response to an internal pressure gradient

A fully 3-dimensional thermal model of a comet nucleus

A 3-D numerical model of comet nuclei is presented. An implicit numerical scheme was developed for the thermal evolution of a spherical nucleus composed of a mixture of ice and dust. The model was tested against analytical solutions, simplified numerical solutions, and 1-D thermal evolution codes. The 3-D code was applied to comet 67P/Churyumov-Gerasimenko; surface temperature maps and the internal thermal structure was obtained as function of depth, longitude and hour angle. The effect of the spin axis tilt on the surface temperature distribution was studied in detail. It was found that for small tilt angles, relatively low temperatures may prevail on near-pole areas, despite lateral heat conduction. A high-resolution run for a comet model of 67P/Churyumov-Gerasimenko with low tilt angle, allowing for crystallization of amorphous ice, showed that the amorphous/crystalline ice boundary varies significantly with depth as a function of cometary latitude.Comment: 19 pages, 10 figure

Ursachen für Kooperation zwischen Organisationen – eine qualitative empirische Untersuchung von Motiven und Verhalten der Beteiligten

Von Kooperationen zwischen Unternehmen erhoffen sich Wirtschaftspolitiker, dass sie als neue Organisationsform die Vorteile von Markt und Hierarchie in sich vereinen und kleine und mittlere Unternehmen durch zeitweilige Zusammenschlüsse größere Wettbewerbsfähigkeit gewinnen. Sie subventionieren Unternehmensverbünde (z. B. Innoregio, 1999 und Kompetenznetzwerke.de, 2000 durch das BMBF, Verbundprojekte auf den Gebieten FuE und Mikroelektronik durch das Land Sachsen) und vergeben zu ihrer Unterstützung Fördermittel für Forschungsprogramme (hier: @virtu im Rahmen der Ausschreibung zur „Arbeitsgestaltung in virtuellen Unternehmen“ durch das BMBF, 2001), aber die ökonomische Bedeutung dieser Organisationsformen ist bisher gering. Umfassende quantitative Befragungen des Zentralverbandes des Deutschen Handwerks (2002) und des Bundesverbandes Deutscher Unternehmensberater (2004) ergaben, dass Kooperationen sich häufig als sehr aufwändig erweisen und leicht zerbrechen bzw. nicht wiederholt werden. Es gilt herauszufinden, warum trotz des großen Nutzens, der durch Zusammenarbeit entstehen kann, Kooperationen nur zögernd eingegangen werden

Zur Verbreitung und Ausgestaltung geringfügiger Beschäftigung im Einzelhandel: eine explorative Studie aus der Perspektive von Management und Beschäftigten

"Geringfügig Beschäftigte im Einzelhandel erleben höchst prekäre Arbeitsbedingungen und weit verbreitete Verstöße gegen das Arbeitsrecht. Das ergab eine explorative Studie auf der Basis von halbstrukturierten Interviews mit Managern und Mitarbeitern in 22 Filialen von 18 verschiedenen Einzelhandelsunternehmen unterschiedlicher Branchen und zwei Unternehmenszentralen in Sachsen. Obwohl nach dem deutschen Arbeitsrecht alle Arbeitnehmer gleich behandelt werden müssen, veranlasst die Arbeitslosenquote von etwa 15 Prozent in der Region die geringfügig Beschäftigten dazu, Löhne zu akzeptieren, die zum Teil nur die Hälfte des Tarifniveaus betragen. Sie erhalten normalerweise kein Urlaubsgeld oder Lohnfortzahlung im Krankheitsfall, werden kurzfristig zur Arbeit gerufen und wieder nach Hause geschickt, erhalten kaum Weiterbildung. Viele von ihnen können jederzeit entlassen werden, da sie über keinen schriftlichen Arbeitsvertrag verfügen. Angesichts von Drohungen, dass Stellen gestrichen und Filialen geschlossen werden könnten, scheinen Betriebsräte nicht auf Erfüllung des Arbeitsrechts zu bestehen. Einige große tarifgebundene Einzelhandelsfirmen entgehen dem Druck der Gewerkschaften auf Einhaltung der Tarife, indem sie die geringfügig Beschäftigten über einen nicht tarifgebundenen Personaldienstleister anstellen." (Autorenreferat)"Mini-jobbers in the retail sector are facing highly precarious working conditions and widespread violation of worker rights. This is what we found in an exploratory study based on semi-structured interviews with managers and employees in 22 outlets of 18 different retail companies and two retail head-offices in Saxony (former East Germany). Even though German labour law requires all employees to be treated equally, the unemployment rate of around 15 percent in the region induces many mini-jobbers to accept wages almost half the collective bargaining rate. As a rule they don't get paid holidays and sickness absence, are called in to work and sent home at short notice, receive hardly any training and can be made redundant any time since many do not have a written work contract. Confronted with managers threatening with job cuts and Shop closures, works councillors do not seem to insist on equal treatment. Some large retailers bound by collective bargaining evade trade union influence by employing their mini-jobbers in the narre of newly founded non-union service companies." (author's abstract

Solar-wind electron precipitation on weakly magnetized bodies: the planet Mercury

Mercury is the archetype of a weakly magnetized, airless, telluric body immersed in the solar wind. Due to the lack of any substantial atmosphere, the solar wind directly precipitates on Mercury's surface. Using a 3D fully-kinetic self-consistent plasma model, we show for the first time that solar-wind electron precipitation drives (i) efficient ionization of multiple species (H, He, O and Mn) in Mercury's neutral exosphere and (ii) emission of X-rays from the planet's surface. This is the first, independent evidence of X-ray auroras on Mercury using a numerical approach.Comment: Submitted to Physical Review Letter

The BepiColombo Environment Radiation Monitor, BERM

The BepiColombo Environment Radiation Monitor (BERM) on board the European Space Agency's Mercury Planetary Orbiter (MPO), is designed to measure the radiation environment encountered by BepiColombo. The instrument measures electrons with energies from similar to 150 keV to similar to 10 MeV, protons with energies from similar to 1.5 MeV to similar to 100 MeV, and heavy ions with Linear Energy Transfer from 1 to 50 MeV.mg(-1).cm(2). BERM is operated continuously, being responsible for monitoring the radiation levels during all phases of the mission, including the cruise, the planetary flybys of Earth, Venus and Mercury, and the Hermean environment. In this paper, we describe the scientific objectives, instrument design and calibration, and the in-flight scientific performance of BERM. Moreover, we provide the first scientific results obtained by BERM during the BepiColombo flyby of Earth in April 2020, and after the impact of a solar energetic particle event during the cruise phase in May 2021. We also discuss the future plans of the instrument including synergies with other instruments on the BepiColombo and on other missions.Peer reviewe

BepiColombo Venus Flyby Science Operations Feasibility Analysis

BepiColombo is an interdisciplinary ESA mission to explore the planet Mercury in cooperation with the Japan Aerospace Exploration Agency (JAXA). The mission consists of 2 spacecraft, ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (MMO) that carry in total 17 science payloads for the investigation of Mercury’s structure, interior, composition, morphology, formation, evolution and environment. The Mercury Composite Spacecraft (MCS) made of MPO, MMO, a Mercury Transfer Module (MTM) and a sunshield (MOSIF) will be launched on an escape trajectory that will bring it into heliocentric orbit on its way to Mercury. During the cruise of 7.2 years toward the inner part of the Solar System, BepiColombo will make 1 flyby to the Earth, 2 to Venus, and 6 to Mercury. Only part of its payload will be obstructed by the sunshield and the cruise spacecraft configuration, so that the flybys will allow operations of many instruments, like: spectrometers at many wavelengths, accelerometer, radiometer, ion and electron detectors. A scientific working group (VFBWG, Venus Fly-by Working Group) has recently formed inside the BepiColombo community to identify potentially interesting scientific cases and to promote collaborations during the Venus flybys. At the same time, analyses of science operations requests has been carried out by the Science Ground Segment (SGS) at ESAC and the Operational Ground Segment (OGS) at ESOC to help scientists in the comprehension of feasibility of proposed investigations. The analysis of science observations includes special spacecraft pointing feasibility analysis taking into account the attitude constraints. During interplanetary cruise and outside electric propulsion, the default attitude of MCS is with +Y axis pointed to the Sun. The spacecraft attitude is then adjusted by ground around the sun line such that the angular momentum loading is minimized while ground contact is maximized during ground station passes. For the short duration of scientific interest around the Venus closest approaches, however, the need for angular momentum load minimization can be relaxed and it is possible to offset the Sun direction in the spacecraft composite +YZ plane. The SGS at ESAC developed a tool that allows to check the possibility of observing Venus in different spacecraft configurations for different instruments, for example finding out when Venus is inside a given instrument FoV. With that tool and based on the scientific instruments pointing requests, candidate pointing timelines were extracted, indicating that it is possible to find a suitable spacecraft composite attitude to provide observing opportunities to most instruments requiring specific spacecraft pointing. In addition, the OGS at ESOC analysed the impact of the received scientific requests on power balance, thermal balance and data return and found well within the as-designed capability of the spacecraft. This paper includes a summary of the scientific requests, the analysis carried out by both SGS and OGS and the results of the analysis

Mercury's Surface Magnetic Field Determined from Proton-Reflection Magnetometry

Solar wind protons observed by the MESSENGER spacecraft in orbit about Mercury exhibit signatures of precipitation loss to Mercury's surface. We apply proton-reflection magnetometry to sense Mercury's surface magnetic field intensity in the planet's northern and southern hemispheres. The results are consistent with a dipole field offset to the north and show that the technique may be used to resolve regional-scale fields at the surface. The proton loss cones indicate persistent ion precipitation to the surface in the northern magnetospheric cusp region and in the southern hemisphere at low nightside latitudes. The latter observation implies that most of the surface in Mercury's southern hemisphere is continuously bombarded by plasma, in contrast with the premise that the global magnetic field largely protects the planetary surface from the solar wind