The Radio Plasma Imager investigation on the IMAGE spacecraft

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique.     

Effect of non-uniform basic temperature gradient on the onset of Marangoni convection in a fluid with suspended particles

The effect of a non-uniform basic temperature gradient on the onset of convection driven by surface tension in a horizontal layer of a Boussinesq fluid with suspended particles confined between an upper free, constant heat flux boundary and a lower rigid isothermal boundary is considered. The microrotation is assumed to vanish at the boundaries. A linear stability analysis is performed. The Rayleigh–Ritz technique is used to obtain the eigenvalues. The influence of various parameters on the onset of convection has been analyzed. Six different non-uniform basic state temperature profiles are considered and their comparative influence on onset is discussed. It is observed that the fluid layer with suspended particles heated from below is more stable compared to the classical fluid layer without suspended particles. The problem has possible applications in microgravity situations.     

The Galaxy Cluster Mass Scale and Its Impact on Cosmological Constraints from the Cluster Population

Space Science Reviews - The QB50 mission is a satellite constellation designed to carry out measurements at between 200–380 km altitude in the ionosphere. The multi-needle Langmuir probe...     

Mass Measurements of Stellar and Intermediate-Mass Black Holes

We discuss the method, and potential systematic effects therein, used for measuring the mass of stellar-mass black holes in X-ray binaries. We restrict our discussion to the method that relies on the validity of Kepler’s laws; we refer to this method as the dynamical method. We briefly discuss the implications of the mass distribution of stellar-mass black holes and provide an outlook for future measurements. Further, we investigate the evidence for the existence of intermediate-mass black holes i.e. black holes with masses above 100 M_⊙, the limit to the black hole mass that can be produced by stellar evolution in the current Universe.     

Planetary Protection and the astrobiological exploration of Mars: Proactive steps in moving forward

Future efforts towards Mars exploration should include a discussion about the effects that the strict application of Planetary Protection policies is having on the astrobiological exploration of Mars, which is resulting in a continued delay in the search for Martian life. As proactive steps in the path forward, here we propose advances in three areas. First, we suggest that a redefinition of Planetary Protection and Special Regions is required for the case of Mars. Particularly, we propose a definition for special places on Mars that we can get to in the next 10–20?years with rovers and landers, where try to address questions regarding whether there is present-day near-surface life on Mars or not, and crucially doing so before the arrival of manned missions. We propose to call those special places “Astrobiology Priority Exploration” regions (APEX regions). Second, we stress the need for the development of robotic tools for the characterization of complex organic compounds as unequivocal signs of life, and particularly new generations of complex organic chemistry and biosignature detection instruments, including advances in DNA sequencing. And third, we advocate for a change from the present generation of SUV-sized landers and rovers to new robotic assets that are much easier to decontaminate such as microlanders: they would be very small with limited sensing capabilities, but there would be many of them available for launch and coordination from an orbiting platform. Implementing these changes will help to move forward with an exploration approach that is much less risky to the potential Mars biosphere, while also being much more scientifically rigorous about the exploration of the “life on Mars” question – a question that needs to be answered both for astrobiological discovery and for learning more definitive lessons on Planetary Protection.     

A comparison of semi-empirical models in the lower thermosphere

Semi-empirical models are derived predominantly from satellite-borne observations. The nature of these observations restricts the applicability of the models mainly to the atmospheric regions sampled, i.e. the upper thermosphere. Current models are only capable of reproducing a zero-order approximation of the structure of the lower thermosphere. Based on selected examples, the progress in atmospheric research since CIRA-72 as well as the continuing deficiencies are demonstrated.     

Travelling heater growth of GaSb under reduced gravity during the first spacelab-mission

Single crystals of binary III-V-semiconductors, e.g. GaAs or InP, are important basic materials for optoelectronic devices, e.g. LED's and lasers. Device production needs highly perfect substrate crystals with low defect densities and homogeneous dopant distributions. In our experiment we applied the Travelling-Heater-Method to grow the III-V compound GaSb. The aim of this research project was to improve the crystal quality by investigating convective transport phenomena and the origins of dopant inhomogeneities under earth and space conditions. Earth grown crystals show strong dopant variations mainly due to convective flow phenomena. The preliminary result of our SPACELAB 1 experiment reveals an increase of dopant homogeneity in the space grown crystal because of the absence of natural convection under reduced gravity.     

Mesospheric ozone densities deduced from solar occultation measurements

Quartz-UV occultation measurements by the satellite Interkosmos-16 have been used to calculate ozone densities at altitudes between 50 and 90 km for the period August to October 1976. Below 65 km densities agree well with the Krueger-Minzner-model. Mesopause densities have been studied in some detail. A certain percentage of the profiles show close correlation with the model of Shimazaki and Laird (with a pronounced minimum below the mesopause) while others fit better to the Park and London model (no minimum). This variability of the ozone density may be caused by different processes in the photo-chemistry of ozone. Two possible causes, the temperature dependent rate coefficients and the odd hydrogen processes are discussed in greater detail.     

GPS modeling for designing aerospace vehicle navigation systems

The complexity of the design of a Global Positioning System (GPS) user segment, as well as the performance demanded of the components, depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system can also affect the user segment design. Models of GPS measurements are used to predict user segment performance at various levels. Design curves are developed which illustrate the relationship between user requirements, the user segment design, and component performance     

Nickel-Cadmium Batteries as Capacitive Filters for Pulsed Loads

This investigation consisted of several tests of specially fabricated nickel-cadmium batteries having circular disk-type electrodes. These batteries were evaluated as filter elements between a constant current power supply and a 5 Hz pulsed load demanding approximately twice the power supply current during the load on a portion of the cycle. Short tests lasting 104 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 J/Ib. In addition, two batteries were subjected to 10h dischar cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode-to-battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 J/Ib, respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10y capacity degradation was negligible for one battery and about 20 percent for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed.