NaK release model for MASTER-2009

Sodium–potassium droplets from the primary coolant loop of Russian orbital reactors have been released into space. These droplets are called NaK droplets. Sixteen nuclear powered satellites of the type RORSAT launched between 1980 and 1988 activated a reactor core ejection system, mostly between 900 and 950 km altitude. The core ejection causes an opening of the primary coolant loop. The liquid coolant consists of eutectic sodium–potassium alloy and has been released into space during these core ejections. The NaK coolant has been forming droplets up to a diameter of 5.5 cm. NaK droplets have been modeled before in ESA's MASTER Debris and Meteoroid Environment Model. The approach is currently revised for the MASTER-2009 upgrade. A mathematical improvement is introduced by substituting the current size distribution function by the modified Rosin–Rammler equation. A bimodal size distribution is derived which is based on the modified mass based Rosin–Rammler equation. The equation is modified by truncating the size range and normalizing over the finite range between the size limits of the smallest and the biggest droplet. The parameters of the model are introduced and discussed. For the validation of the NaK release model, sixteen release events are simulated. The resulting size distribution is compared with radar measurement data. The size distribution model fits well with revised published measurement data of radar observations. Results of orbit propagation simulation runs are presented in terms of spatial density.     

Hemodynamic and neurohormonal responses to extreme orthostatic stress in physically fit young adults

Blood pressure stability may be jeopardized in astronauts experiencing orthostatic stress. There is disagreement about cardiovascular and endocrine stress responses that emerge when a critical (presyncopal) state is reached. We studied hemodynamic and neurohormonal changes as induced by an orthostatic stress paradigm (head-up tilt combined with lower body negative pressure) that leads to a syncopal endpoint. From supine control to presyncope, heart rate increased by 78% and thoracic impedance by 12%. There was a 49% fall in stroke volume index, 19% in mean arterial blood pressure, 14% in total peripheral resistance index and 11% in plasma volume. Plasma norepinephrine rose by 107, epinephrine by 491, plasma renin activity by 167, and cortisol by 25%. Hemodynamic and hormonal changes of clearly different magnitude emerge in presyncope as compared to supine rest. Additional studies are warranted to reveal the exact time course of orthostatic changes up to syncopal levels.     

Geoscience for Understanding Habitability in the Solar System and Beyond

Space Science Reviews - This paper reviews habitability conditions for a terrestrial planet from the point of view of geosciences. It addresses how interactions between the interior of a planet or...     

Scaling Relations from Stellar to Supermassive Black Holes

Accretion is a ubiquitous phenomenon—it is seen in sources ranging from young stars to accreting supermassive black holes in the centres of galaxies. Here, we present the known empirical connections between stellar mass X-ray binaries and active galactic nuclei. We argue that this implies that both the accretion disc and the jet are scale invariant with respect to the black hole mass. Finally, we show that also accretion discs and jets in sources with a different accretor can be connected empirically to accreting black holes, hinting towards a common mechanism of accretion in all sources.     

Recent Evidence for Convection in Sunspot Penumbrae

Whereas penumbral models during the last 15 years have been successful in explaining Evershed flows and magnetic field inclination variations in terms of flux tubes, the lack of contact between these models and a convective process needed to explain the penumbral radiative heat flux has been disturbing. We report on recent observational and theoretical evidence that challenge flux tube interpretations and conclude that the origin of penumbral filamentary structure is overturning convection.     

Energisation of O+ and O+ 2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation

We have studied the loss of O⁺ and O⁺ ₂ ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H⁺, He⁺⁺, O⁺, O⁺ ₂) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft have measured the proprieties of escaping atomic and molecular ions, in particular O⁺ and O⁺ ₂ ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed at Mars.     

RPC-LAP: The Rosetta Langmuir Probe Instrument

The Rosetta dual Langmuir probe instrument, LAP, utilizes the multiple powers of a pair of spherical Langmuir probes for measurements of basic plasma parameters with the aim of providing detailed knowledge of the outgassing, ionization, and subsequent plasma processes around the Rosetta target comet. The fundamental plasma properties to be studied are the plasma density, the electron temperature, and the plasma flow velocity. However, study of electric fields up to 8 kHz, plasma density fluctuations, spacecraft potential, integrated UV flux, and dust impacts is also possible. LAP is fully integrated in the Rosetta Plasma Consortium (RPC), the instruments of which together provide a comprehensive characterization of the cometary plasma. The LAP Team is listed in Table III.     

Global Non-Potential Magnetic Models of the Solar Corona During the March 2015 Eclipse

Seven different models are applied to the same problem of simulating the Sun’s coronal magnetic field during the solar eclipse on 2015 March 20. All of the models are non-potential, allowing for free magnetic energy, but the associated electric currents are developed in significantly different ways. This is not a direct comparison of the coronal modelling techniques, in that the different models also use different photospheric boundary conditions, reflecting the range of approaches currently used in the community. Despite the significant differences, the results show broad agreement in the overall magnetic topology. Among those models with significant volume currents in much of the corona, there is general agreement that the ratio of total to potential magnetic energy should be approximately 1.4. However, there are significant differences in the electric current distributions; while static extrapolations are best able to reproduce active regions, they are unable to recover sheared magnetic fields in filament channels using currently available vector magnetogram data. By contrast, time-evolving simulations can recover the filament channel fields at the expense of not matching the observed vector magnetic fields within active regions. We suggest that, at present, the best approach may be a hybrid model using static extrapolations but with additional energization informed by simplified evolution models. This is demonstrated by one of the models.     

Models for Type Ia Supernovae and Related Astrophysical Transients

We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we comment on some of the successes and shortcoming of these scenarios and highlight important outstanding issues.