Hard X-ray balloon observations of compact galactic and extragalactic X-ray sources

A balloon program in hard X-ray astronomy (20–200 keV) is jointly pursued by the Astronomisches Institut der Universität Tübingen (AIT) and the Max Planck-Institute für Extraterrestrische Physik in Garching (MPE). Since 1973 nine successful balloon flights have been performed from Texas and Australia. Here results on Centaurus A and on several galactic binary X-ray sources are summarized. In particular the high energy photon spectrum of Hercules X-1 and the evidence for the cyclotron line feature which was discovered by us in 1976 is reviewed.     

Mupus – A Thermal and Mechanical Properties Probe for the Rosetta Lander Philae

MUPUS, the multi purpose sensor package onboard the Rosetta lander Philae, will measure the energy balance and the physical parameters in the near-surface layers – up to about 30 cm depth- of the nucleus of Rosetta’s target comet Churyumov-Gerasimenko. Moreover it will monitor changes in these parameters over time as the comet approaches the sun. Among the parameters studied are the density, the porosity, cohesion, the thermal diffusivity and conductivity, and temperature. The data should increase our knowledge of how comets work, and how the coma gases form. The data may also be used to constrain the microstructure of the nucleus material. Changes with time of physical properties will reveal timescales and possibly the nature of processes that modify the material close to the surface. Thereby, the data will indicate how pristine cometary matter sampled and analysed by other experiments on Philae really is.     

Interstellar Dust in the Solar System

The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79°, perihelion distance 1.3 AU, aphelion distance 5.4 AU) since it encountered Jupiter in 1992. The in situ dust detector on board continuously measured interstellar dust grains with masses up to 10⁻¹³ kg, penetrating deep into the solar system. The flow direction is close to the mean apex of the Sun’s motion through the solar system and the grains act as tracers of the physical conditions in the local interstellar cloud (LIC). While Ulysses monitored the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the time varying interplanetary magnetic field. We review the results from in situ interstellar dust measurements in the solar system and present Ulysses’ latest interstellar dust data. These data indicate a 30° shift in the impact direction of interstellar grains w.r.t. the interstellar helium flow direction, the reason of which is presently unknown.     

Application of an evolution strategy in planetary ephemeris modeling

Classical planetary ephemeris construction comprises three major steps which are to be performed iteratively: numerical integration of coupled equations of motion of a multi-body system (propagator step), reduction of observations (reduction step), and optimization of model parameters (adjustment step). In future, this approach may become challenged by further refinements in force modeling (e.g. inclusion of much more significant minor bodies than in the past), an ever-growing number of planetary observations (e.g. the vast amount of spacecraft tracking data), and big data issues in general. In order to circumvent the need for both the inversion of normal equation matrices and the determination of partial derivatives, and to prepare the ephemeris for applications apart from stand-alone solar-system planetary orbit calculations, here we propose an alternative ephemeris construction method. The main idea is to solve it as an optimization problem by straightforward direct evaluation of the whole set of mathematical formulas, rather than to solve it as an inverse problem with all its tacit mathematical assumptions and potential numerical difficulties. The usual gradient search is replaced by a stochastic search, namely an evolution strategy, the latter of which is perfect for the exploitation of parallel computing capabilities. Furthermore, this new approach allows for multi-criteria optimization and time-varying optima. These issues will become important in future once ephemeris construction is just one part of even larger optimization problems, e.g. the combined and consistent determination of a generalized physical state (orbit, size, shape, rotation, gravity, $\dots$) of celestial bodies (planets, satellites, asteroids, or comets), and/or if one seeks near real-time solutions. Here, we outline the general idea and exemplarily optimize high-correlated asteroidal ring model parameters (total mass and heliocentric radius), and individual asteroid masses, based on simulated observations.     

The Mars Odyssey Gamma-Ray Spectrometer Instrument Suite

The Mars Odyssey Gamma-Ray Spectrometer is a suite of three different instruments, a gamma subsystem (GS), a neutron spectrometer, and a high-energy neutron detector, working together to collect data that will permit the mapping of elemental concentrations on the surface of Mars. The instruments are complimentary in that the neutron instruments have greater sensitivity to low amounts of hydrogen, but their signals saturate as the hydrogen content gets high. The hydrogen signal in the GS, on the other hand, does not saturate at high hydrogen contents and is sensitive to small differences in hydrogen content even when hydrogen is very abundant. The hydrogen signal in the neutron instruments and the GS have a different dependence on depth, and thus by combining both data sets we can infer not only the amount of hydrogen, but constrain its distribution with depth. In addition to hydrogen, the GS determines the abundances of several other elements. The instruments, the basis of the technique, and the data processing requirements are described as are some expected applications of the data to scientific problems.     

Cosima – High Resolution Time-of-Flight Secondary Ion Mass Spectrometer for the Analysis of Cometary Dust Particles onboard Rosetta

The ESA mission Rosetta, launched on March 2nd, 2004, carries an instrument suite to the comet 67P/Churyumov-Gerasimenko. The COmetary Secondary Ion Mass Anaylzer – COSIMA – is one of three cometary dust analyzing instruments onboard Rosetta. COSIMA is based on the analytic measurement method of secondary ion mass spectrometry (SIMS). The experiment’s goal is in-situ analysis of the elemental composition (and isotopic composition of key elements) of cometary grains. The chemical characterization will include the main organic components, present homologous and functional groups, as well as the mineralogical and petrographical classification of the inorganic phases. All this analysis is closely related to the chemistry and history of the early solar system. COSIMA covers a mass range from 1 to 3500 amu with a mass resolution m/Δm @ 50% of 2000 at mass 100 amu. Cometary dust is collected on special, metal covered, targets, which are handled by a target manipulation unit. Once exposed to the cometary dust environment, the collected dust grains are located on the target by a microscopic camera. A pulsed primary indium ion beam (among other entities) releases secondary ions from the dust grains. These ions, either positive or negative, are selected and accelerated by electrical fields and travel a well-defined distance through a drift tube and an ion reflector. A microsphere plate with dedicated amplifier is used to detect the ions. The arrival times of the ions are digitized, and the mass spectra of the secondary ions are calculated from these time-of-flight spectra. Through the instrument commissioning, COSIMA took the very first SIMS spectra of the targets in space. COSIMA will be the first instrument applying the SIMS technique in-situ to cometary grain analysis as Rosetta approaches the comet 67P/Churyumov-Gerasimenko, after a long journey of 10 years, in 2014.     

双组元高室压脉冲火箭发动机工作特性分析

为了研究高室压脉冲火箭发动机的工作特性,在分析其工作原理的基础上建立了数学模型,其中燃烧室和挤压腔采用零维模型,喷管采用一维准稳态模型,采用四阶Runge-Kutta法进行了求解.结果表明,燃烧室的最大压强和平均压强都高于推进剂供给压强,而挤压过程中进出燃烧室的质量不守恒是压强升高的原因.与常规液体火箭发动机相比较表明,脉冲火箭发动机的真空比冲提高了7.5%,而喉部面积仅为其10.2%.     

Detection of iron lines in the persistent emission of some X-ray burst sources observed by EXOSAT

We have observed the X-ray burst sources 4U1728-33 and 4U1813-14 with the ME detectors aboard EXOSAT, and present here results of a spectral analysis of their persistent emissions. For both sources the data can be well fitted by a double blackbody continuum and a Gaussian emission line. The two spectral components can be interpreted in terms of a blackbody radiation from the neutron star, and emission from the inner part of an accretion disc. The line feature is consistent with the 6.7 keV iron emission line expected in the presence of a hot extended object (X-ray corona) around the neutron star.     

Development status and application of the electric propulsion system RIT-10 used for station-keeping

The German 10 mN high frequency ion thruster system RIT-10 designed at Giessen University, constructed at MBB, and tested essentially at DFVLR, has attained an engineering model status and stands shortly before qualification for space flight. First application is planned for RIT-10 as a north-south stationkeeping system in TV-Sat preoperational version where it is flown as an experiment in order to acquire experience for subsequent operational communication satellite missions. The paper first describes the existing hardware, then shortly discusses application aspects, the respective test program, and preflight and flight procedures considered to guarantee safe and efficient operation in space.     

The flux of interstellar dust observed by Ulysses and Galileo

Interstellar dust detected by the dust sensor onboard Ulysses was first identified after the Jupiter flyby when the spacecraft's trajectory changed dramatically (Grün et al., 1994). Here we report on two years of Ulysses post-Jupiter data covering the range of ecliptic latitudes from 0° to –54° and distances from 5.4 to 3.2 AU. We find that, over this time period, the flux of interstellar dust particles with a mean mass of 3·10^–13 g stays nearly constant at about 1·10^–4, m^–2 s^–1 ( sr)^–1, with both ecliptic latitude and heliocentric distance.Also presented are 20 months of measurements from the identical dust sensor onboard the Galileo spacecraft which moved along an in-ecliptic orbit from 1.0 to 4.2 AU. From the impact direction and speeds of the measured dust particles we conclude that Galileo almost certainly sensed interstellar dust outside 2.8 AU; interstellar particles may also account for part of the flux seen between 1 and 2.8 AU.