COSAC onboard Rosetta: a bioastronomy experiment for the short-period comet 67P/Churyumov-Gerasimenko

The COSAC (Cometary Sampling and Composition Experiment) onboard the Rosetta mission is a combined gas chromatograph (GC)-mass spectrometer (MS). It is situated on Philae, the lander of the mission, which is intended to land on the nucleus of comet 67P/Churyumov- Gerasimenko. The purpose of the experiment is to analyze the volatile fraction of soil samples retrieved by a drill. For investigation, the samples will be pyrolysed, and the emanating gases fed into a GC, into an MS, or the combination of both. In the first part of this paper, the bioastronomical relevance of such measurements is outlined. In the second part the details of the hardware and its performance are described.     

Radioisotope-powered free-piston Stirling engine for space applications

The paper presents a preliminary conceptual design of a 2kW(e) autonomous power system consisting of a radioisotopic heat source, free-piston Stirling engine, reciprocating induction generator and a space radiator. The proposed design features a direct thermal interfacing of the Pu-238 heat source with the Stirling engine head, low heat losses during normal operation, and provides an auxiliary/emergency cooling system in the case of the engine failure of stopping. The Stirling engine is of the free-displacer, free-piston type invented by Beale and uses helium as the working fluid. The engine piston is integrated with the armature of a simple linear alternator which is used for electric generation. Waste heat is rejected by a four-finned space radiator sized for a geosynchronous orbit. Specific power and efficiency of the Stirling isotope power system are compared with the present and predicted performance of other power conversion systems suitable for the same power range.     

Angular Velocity Measurement Using Rate Gyros in a Spinning Vehicle

It is shown that when the gyro spin vector is in opposition to the spin vector of the vehicle, the output differential equation of the gyro becomes unstable for large vehicle spin values. When the gyro is used with its spin vector along the spin vector of the vehicle, the steady-state response of the gyro is a nonlinear function of the roll rate of the vehicle.     

Empirical models of the thermosphere and requirements for improvements

The different types of variation in the thermosphere are briefly examined and the solar-activity effect is singled out for special attention. To this day, empirical models have made use of the decimetric solar flux F_10.7 as an index of the variable XUV radiation from the sun. To account for the change in the relative intensity of the different types of emissions in the course of the solar cycle, F_10.7 is made to perform double duty: The daily values are used to represent the day-to-day and “27-day” variations, while its averages over several solar rotations are used to represent the variations with the 11-year cycle. The availability of direct solar XUV data should eventually eliminate the need for such a make-shift procedure. Accuracy and continuity requirements of XUV intensity measurements are discussed and a strategy is outlined for sorting out the relevant features from the observational material and putting them to practical use in thermospheric modeling. It is suggested that future models of the diurnal and the geomagnetic variation use as a guide theoretical models which have achieved considerable success in qualitatively representing the observed phenomena.     

The X-ray background 2–50 kev: A superposition of known sources,or evidence of a new component?

The contribution of the canonical Quasars to the XRB 2–50 keV is not likely to exceed 50%. Nay, consideration of X-ray selection effects results in a further reduction of the value of sensible estimators for the intensity ratio L_X/L_O; in addition, recent counts of radioloud and radio-quiet Quasars definitely limit the number of faint sources. A missing component with definite spectral properties should comprise a sizeable fraction of the XRB.     

Enhanced Power Generation of GSS4PS by Optical Solar Reflectors

A novel arrangement is proposed to enhance the power generation capabilities of a gravitationally stabilized solid-state-satellite solar-power station (GSS4PS) spherical solar collector. The unilluminated portion of a GSS4PS is illuminated by employing optical solar reflectors. The different mechanisms required for implementation of this arrangement are already space proven. The detailed study of this arrangement made by the authors reveals that practical realization of this concept will enhance the power generation capability of the GSS4PS and simultaneously reduce the weight per unit power and cost per unit power in GSS4PS spherical solar collectors.     

Diamagnetic aspects of the coronal transient phenomenon

If a magnetic structure emerges into the solar atmosphere containing a preexisting magnetic field, the preexisting field must be moved aside to allow space for the emerging flux. Under these conditions, provided the ambient field strength decreases outward with radial distance, the ambient field may tend to pinch off the emerging field through magnetic reconnection and expell it outward. Here, a model is developed to demonstrate this effect and to evaluate its relevance to the coronal transient phenomenon. In particular, we argue that, if magnetic reconnection can be initiated in such a configuration, the upward force produced by the ambient field is enhanced and, depending upon the internal conditions of the configuration, a coronal transient could be initiated in this manner.     

On a distorted flame front as a hydrodynamic discontinuity

The radius of curvature of a steady distorted flame often turns out to be considerably larger than the width of the thermal structure of the flame. Thus, even under finite deformations of the flame, its structure remains quasi-one-dimensional. This property enables the propagation velocity of a distorted flame front (relative to the gas) to be determined explicitly as a function of the hydrodynamic field and the physico-chemical parameters of the gaseous mixture. With the aid of this relationship one can try to determine the shape of the front in a model which is external with respect to the flame structure and treats the flame as a density jump in an ideal incompressible fluid. As applications, we consider (1) the structure of a Bunsen cone, (2) the extinction of a flame in a divergent flow and (3) the propagation velocity of a corrugated flame.