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Thermal dual-probes are frequently used to measure the heat capacity and diffusivity of soil samples. These probes mostly consist of two thin parallel needles, one serving as a heater and the other as a temperature sensor. Originally a simple infinite line source model was applied to describe the temperature evolution around the heated needle and to evaluate dual-probe measurements. Quite recently an analytical approach by Knight et al. (2012) for the infinitely long dual-probe made it possible to take the finite radius and heat capacity of the probes into account. In the present article this theory is extended to allow for surface resistances at the boundaries between the probes and the sample and, in addition, facilitating a subdivision of the probes into cylindrical cores and surrounding tubular sheaths, which is a rough representation of the needles’ inner structure. In comparison with computer simulations by finite element solvers, the extended semi-analytical approach enables us to determine the influence of contact resistances with shorter computation time, providing an efficient method for the evaluation of dual-probe measurements.

The STEREO/WAVES experiment is considered to provide measurements of the non-thermal radio spectrum from a few kHz up to about 16 MHz, performed by three 6-m long orthogonal monopole antennas and a set of receivers (fixed-, high-, and low frequency receiver). This system performs real-time calculation of antenna voltage coherence products and, then, enables the determination of direction of arrival and polarization state of incident radio waves. Analysis of such kind of antenna system is necessary in order to define the reception properties which crucially depend on the overall spacecraft configuration. The concept of effective length vector ( h eff ) determination is applied to yield corresponding information on the deviation of h eff from the physical rods, in dependence of frequency. Various methods are evaluated (rheometry for frequencies up to 1 MHz), wire-grid modelling and in-flight calibration, and their implication to the SWAVES experiment are discussed.

The search for lightning on Saturn's satellite Titan is one scientific target of the Cassini/Huygens mission. Although Voyager 1 did not detect any radio emissions caused by Titan lightning during its flyby in November 1980, one cannot generally rule out their existence, because of low flash rates or ionospheric radiation blockade. Recently, Tokano et al. (Planet. Space Sci. 49 (2001a) 539) have developed a thundercloud model in Titan's troposphere favoring the existence of Titan lightning due to negatively charged clouds causing temporary electric fields sufficient to initiate cloud-to-ground lightning strokes. In the present investigation we estimate the amount of energy dissipation of such lightning strokes by electrostatic energy considerations similarly to those by Cooray (J. Geophys. Res. 102(D17) (1997) 21,401). The analysis is based on the cloud charge distribution given by Tokano et al. (2001a), which has a monopole structure or a dipole structure depending on the electrification mechanism. It consists of horizontally homogenous charge layers, whose charge densities depend on the altitude above ground. As results we get the typical charge lowered in a possible Titan lightning stroke and the amount of energy dissipation. For a simulated Titan monopolar cloud charged by electron attachment we found that cloud-to-ground strokes lower about 30 C of charge and dissipate energies about 10 10 J . For the modelled bipolar clouds charged by collisional charging these values are a few C of lowered charge and about 108–109J of dissipated energy, which are quite similar to typical Earth values. These energies are substantially higher than the energies suggested by Desch and Kaiser (Nature 343 (1990) 442), who concluded from the Voyager data that discharges might be frequent but weak ( 16 MHz during the propagation through Titan's ionosphere as calculated by Schwingenschuh et al. (Adv. Space Res. 28(10) (2001) 1505).

It is well known that in contrast to the Alfven wave, which is propagating strictly along the direction of the magnetic field, a slow mode wave shows a deviation from the ambient magnetic field. This deviation is determined by the dispersion equation for the slow mode wave. With the help of this dispersion equation we present a theoretical study of the spatial and temporal evolution of an initial pressure disturbance in a homogeneous and constant background magnetic field. The main factor determining the amount of the deviation is the so-called plasma beta, i.e., the ratio of magnetic to thermal energy, which is investigated quantitatively. We obtain that for a low beta plasma, the disturbance propagates more or less strictly along the magnetic field. However, for increasing beta the disturbances across the magnetic field gets stronger. These results can be applied to magnetospheric phenomena, where slow shocks may play a role as a kind of energy carrier as in the case of the Io–Jupiter interaction or magnetic field line reconnection.

The first — and possibly deepest — in situ science measurements on the 46P/Wirtanen nucleus will be made by two sensors of the Rosetta Lander's MUPUS experiment. A piezoelectric shock accelerometer (ANC-M) and a resistance temperature sensor (ANC-T) will be mounted in the Lander's harpoon anchor. This will be shot into the surface at about 60 m s −1 on touchdown, reaching a final depth of between a few centimetres and about 2.5 m, depending on the hardness of the ground and the maximum available cable length. Early indications of the strength of the surface material and any distinct layers should prove valuable to subsequent depth-sensitive investigations, including the MUPUS thermal probe, seismic sounding experiments, the sampling drill and composition analyses of the extracted material. Interpretation of the ANC-M data will help to constrain models of the formation and evolution of the material found at the landing site and document the mechanical and structural context of nearby sampled material. We report on the results of recent test shots performed with a prototype anchor into several porous materials: two types of glass foam, H2O ice and CO2 ice. With the help of data from direct shear tests and quasi-static penetration tests, we interpret the processed deceleration data using a cavity-expansion penetration model. Layers of distinctly different strengths can be detected and located, and the deceleration profiles are in reasonable agreement with the profiles obtained by quasi-static tests. The anchor projectile's long sharp tip tends to smear out the boundaries, however. In applying the penetration model we found that the coefficient of sliding friction and the target's volumetric strain have a much stronger influence on the deceleration profile than the initial target density and angle of internal friction. Very small values of volumetric strain (corresponding to high ‘drag coefficient’) were required to fit deceleration profiles to the measured data for the glass foam, contrary to what we initially expected by inspecting the thin layer of crushed material around the walls of the penetrated channel. We interpret this to mean that such brittle, porous materials as the glass foam (and perhaps highly porous, brittle, cryogenic ice) do not exhibit plastic deformation before failing completely by the crushing of cell walls. The decelerating forces are thus thought to be dominated by momentum transfer to the crushed material and by the crushing strength of the cellular microstructure, rather than by the force required to deform the target plastically. The cavity-expansion model seems to be well-suited to the ice shots, but for the brittle, cellular glass foam, alternative approaches, taking into account the material's microstructure, are needed. As a first step in this direction, a microstructural model linking textural properties of the material (pore and grain size, and relative contact area between grains) is applied to the glass foam data, obtained from quasi-static penetration tests and from direct shear strength tests. It is demonstrated that the dependence of strength on porosity can be well represented by the model suggested. A microstructural model for sintered ices, relating strength properties to porosity and thermal properties, would be useful for interpretation of MUPUS ANC-M data in the context of other physical properties measurements. The work presented here may also have some relevance to the design of future comet landers or penetrators. The harpoon anchor/penetrometer approach could be employed on other minor body landing missions, while the modelling technique is similar in many ways to that appropriate for other penetrometers/penetrators.

In the years 2011–2013 the ESA mission Rosetta will explore the short period comet 46P/Wirtanen. The aims of the mission include investigation of the physical and chemical properties of the cometary nucleus and also the evolutionary processes of comets. It is planned to land a small probe on the surface of the comet, carrying a multitude of sensors devoted to in situ investigation of the material at the landing site. On touchdown at the nucleus, an anchoring harpoon will be fired into the surface to avoid a rebound of the lander and to supply a reaction force against mechanical operations such as sample drilling or instrument platform motion. The anchor should also prevent an ejection of the lander due to gas drag from sublimating volatiles when the comet becomes more active closer to the Sun. In this paper, we report on the development of one of the sensors of the MUPUS instrument aboard the Rosetta Lander, the MUPUS ANC-M (mechanical properties) sensor. Its purpose is to measure the deceleration of the anchor harpoon during penetration into the cometary soil. First the test facilities at the Max-Planck-Institute for Extraterrestrial Physics in Garching, Germany, are briefly described. Subsequently, we analyse several accelerometer signals obtained from test shots into various target materials. A procedure for signal reduction is described and possible errors that may be superimposed on the true acceleration or deceleration of the anchor are discussed in depth, with emphasis on the occurrence of zero line offsets in the signals. Finally, the influence of high-frequency resonant oscillations of the anchor body on the signals is discussed and difficulties faced when trying to derive grain sizes of granular target materials are considered. It is concluded that with the sampling rates used in this and several other space experiments currently under way or under development a reasonable resolution of strength distribution in soil layers can be achieved, but conclusions concerning grain size distribution would probably demand much higher sampling rates.