Solar wind interaction with comet Halley

In March 6 and 9, 1986 the spacecrafts ‘Vega-1’ and ‘Vega-2’ have flown through the coma of comet Halley and have carried measurements of plasma, energetic particles, magnetic field and plasma waves along its trajectory. A short review of these measurements and its comparison with theoretical models of solar wind interaction with comets are given.

The spacecrafts ‘Vega-1’ and ‘Vega-2’ have studied the solar wind loading by cometary ions, the structure of cometary bow shock and the processes in the inner coma of comet Halley. Exactly in this sequence we discuss the results of measurements and compare them with the theory.     

Wave and plasma measurements on the Vega-1 and Vega-2 spacecraft in the environment of comet Halley

The Vega-1 and Vega-2 wave and plasma measurements performed on 6 and 9 March 1986 in the environment of comet Halley present similar characteristics. Field spectral intensity of up to $\text{5}\text{mVm}{}^{\mathrm{?1}}\text{Hz}{}^{\mathrm{?}}\text{1}\text{2}$ at 300 Hz is measured at closest approach; enhanced signals are detected in the whistler mode and in the vicinity of the lower hybrid resonance frequency within respective average distances of 130,000 km and 60,000 km from the nucleus. The plasma density rises from 100 cm^?3 at 200,000 km up to 3000 cm^?3 at 25,000 km. The spacecraft potential is of the order of +3 V beyond a distance of 200,000 km and decreases to about +0.5 V at 8,000 km.     

LEO原子氧对空间材料侵蚀的数值模拟

提出了吸附作用(包括物理吸附和化学吸附)是引起空间材料原子氧腐蚀的主要机理.以此为依据,建立了相应的腐蚀量的反应-扩散方程.应用分子动力学经典碰撞理论的估算表明了方程中的物理作用项对于扩散效应为一小量,从而进一步简化了方程.在所建立的模型方程中,选用了基于Eyring绝对速率理论的扩散系数.对空间表面材料Kapton在近地轨道LEO(Low Earth Orbit)环境受原子氧侵蚀的过程进行了数值模拟,计算结果与飞行试验数据在误差允许的范围内符合得较好.     

Status of the Stratospheric Observatory for Infrared Astronomy (SOFIA)

The Stratospheric Observatory for Infrared Astronomy (SOFIA), a joint US/German project, is a 2.5-m infrared airborne telescope carried by a Boeing 747-SP that flies in the stratosphere at altitudes as high as 45,000 ft (13.72 km). This facility is capable of observing from 0.3 μm to 1.6 mm with an average transmission greater than 80% averaged over all wavelengths. SOFIA will be staged out of the NASA Dryden Flight Research Center aircraft operations facility at Palmdale, CA. The SOFIA Science Mission Operations (SMO) will be located at NASA Ames Research Center, Moffett Field, CA. First science flights began in 2010 and a full operations schedule of up to one hundred 8 to 10 hour-long flights per year will be reached by 2014. The observatory is expected to operate until the mid-2030s. SOFIA’s initial complement of seven focal plane instruments includes broadband imagers, moderate-resolution spectrographs that will resolve broad features due to dust and large molecules, and high-resolution spectrometers capable of studying the kinematics of atomic and molecular gas at sub-km/s resolution. We describe the SOFIA facility and outline the opportunities for observations by the general scientific community and for future instrumentation development. The operational characteristics of the SOFIA first-generation instruments are summarized. The status of the flight test program is discussed and we show First Light images obtained at wavelengths from 5.4 to 37 μm with the FORCAST imaging camera. Additional information about SOFIA is available at http://www.sofia.usra.edu and http://www.sofia.usra.edu/Science/docs/SofiaScienceVision051809-1.pdf.     

Improved orbital parameters of accreting millisecond pulsar SAX J1808.4-3658

We analyze the three outbursts of the X-ray millisecond pulsar SAX J1808.4-3658 that occurred in 1998, 2000, and 2002 observed with RXTE. With a technique based on epoch folding search we find an unique orbital solution valid over the five years of high temporal resolution data available. We revise the estimate of the orbital period, P_orb = 7249.1569(1) s and of its error, which we decrease by one order of magnitude. We also give the first constraint on the orbital period derivative, . We find that in 2002 the pulse profile shape is clearly asymmetric, showing a secondary peak at about 145° from the main pulse, which is different from the sinusoidal shape reported at the beginning of the 1998 outburst.     

Modeling the solar cosmic ray event of 13 December 2006 using ground level neutron monitor data

In order to understand the physics under extreme solar conditions such as those producing ground level enhancements of solar cosmic rays, it is important to use accurate and reliable models. The NM-BANGLE Model is a new cosmic ray model which couples primary solar cosmic rays at the top of the Earth’s atmosphere with the secondary ones detected at ground level by neutron monitors during GLEs. This model calculates the evolution of several GLE parameters such as the solar cosmic ray spectrum, anisotropy and particle flux distribution, revealing crucial information on the energetic particle propagation and distribution. The total output of the NM-BANGLE Model is a multi-dimensional GLE picture that gives an important contribution to revealing the characteristics of solar energetic particle events recorded at ground level. In this work, the results of the NM-BANGLE Model application to the recent GLE of 13 December 2006 are presented and discussed. Moreover, a comparison with the extreme event of 20 January 2005 (GLE69) has been realized.     

进气道结构对固体冲压发动机补燃室燃烧及内壁流场的影响

为研究进气道结构对固体冲压发动机补燃室燃烧及内壁烧蚀的影响,采用标准k-ε湍流模型,单步涡耗散燃烧模型与KING硼粒子点火燃烧模型,开展了双下侧90°进气结构和双侧180°进气结构固体冲压发动机补燃室内燃气燃烧数值模拟,对比分析了补燃室燃气燃烧流场特征和内壁烧蚀环境特征。结果表明:双侧180°进气结构在补燃室中形成大漩涡,有利于燃气与空气的掺混燃烧,至补燃室出口位置,总燃烧效率超过90%,且该结构有效减少了粒子对内壁的冲刷侵蚀;在双下侧90°进气结构补燃室中,凝聚相粒子和燃气贴近补燃室一侧运动,导致氧气浓度和温度分布不均,不利于燃气的掺混燃烧,总燃烧效率为74%,在远离补燃室进气道一侧形成高温热烧蚀、高浓度粒子侵蚀、高速射流冲刷和热应力集中的综合破坏;双侧180°进气结构的固体冲压发动机补燃室总体性能优于双下侧90°进气结构的冲压发动机补燃室。      

Precise measurements of the cosmic ray antiproton spectrum with BESS including the effects of solar modulation

The Balloon Borne Experiment with a Superconducting Spectrometer (BESS) has measured the energy spectrum of cosmic-ray antiprotons between 0.18 and 4.20 GeV in eight flights between 1993 and 2002. Above about 1 GeV, models in which antiprotons are secondary products of the interactions of primary cosmic rays with the interstellar gas agree with the BESS antiproton spectrum. Below 1 GeV, the data show a possible excess antiproton flux compared to secondary model predictions, suggesting the presence of an additional source of antiprotons. The antiproton/proton ratios measured between 1993 and 1999, during the Sun’s positive-polarity phase, are consistent with simple models of solar modulation. However, results from the 2000 flight, following the solar magnetic field reversal, show a sudden increase in the antiproton/proton ratio and tend to favor a charge-sign-dependent drift model. To extend BESS measurements to lower energies, an evolutionary instrument, BESS-Polar, is under construction for polar flight in 2004.     

Analysis of cytogenetic effects of the secondary radiation resulting from 70 GeV protons of Chinese hamster cells.

The cell culture of a Chinese hamster was irradiated on a Serpuchov proton synchrotron at a dose of 0.5-4 Gy and a dose rate of 1 Gy/min and by gamma-irradiation at dose 1-5 Gy and dose rate 1.2-1.4 Gy/min. The effect of radiation on the cell culture was judged from chromosomal aberrations in G2-stage of cell cycle and micronuclear test. The relative biological efficience of the secondary radiation was approximately 3. Modifying effect of caffeine on the cells irradiated by secondary radiation of synchrotron was not observed. In the presence of caffeine the effect of gamma-irradiation practically is increased up to the level observed upon secondary irradiation. This suggests that secondary radiation inhibits the repair of the cytogenetic damage.     

Development of an extreme ultraviolet imaging spectrometer for the BepiColombo mission

Extreme and far ultraviolet imaging spectrometers are proposed for the low-altitude orbiter of the BepiColombo mission. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring (1) emission lines from molecules, atoms and ions present in the Mercury’s tenuous atmosphere and (2) the reflectance spectrum of Mercury’s surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30–150 nm with the field of view of 5.0°, and the spectrum from 130 to 430 nm is obtained by the far UV spectrometer. The extreme UV spectrometer employs multi-layer coating technology to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signatures such as He II (30.4 nm) and Na II (37.2 nm), which could not be detected with conventional optics.     

Solar wind velocity measurements near the sun using Ulysses radio amplitude correlations at two frequencies

Measurements of solar wind velocity have been derived from simultaneous coronal sounding observations of radio amplitude scintillations at both S-band and X-band during the solar conjunction of the Ulysses spacecraft in August 1991. The signal amplitude was recorded with an averaging time of 1 s. A cross-correlation analysis between S- and X-band amplitude fluctuations shows that the fluctuation signature at S-band appears to be shifted to earlier times with respect to the X-band recording. The time difference is proportional to the coronal separation of the ray paths and inversely proportional to the apparent velocity of plasma inhomogeneities across the ray paths. Preliminary estimates of solar wind speed obtained using model calculations of the differential refraction are found to lie near the expected transition from subsonic to supersonic velocities at solar offset distances of the order of 6–8 R. As a byproduct of the investigation, we find that the transition from weak to saturated scintillation occurs at about 16 R for S-band and 7 R for X-band.     

An analytical model for the prediction of a micro-dosimeter response function

A rapid analytical procedure for the prediction of a micro-dosimeter response function in low Earth orbit (LEO), correlated with the Space Transportation System (STS, shuttle) Tissue Equivalent Proportional Counter (TEPC) measurements is presented. The analytical model takes into consideration the energy loss straggling and chord length distribution of the detector, and is capable of predicting energy deposition fluctuations in a cylindrical micro-volume of arbitrary aspect ratio (height/diameter) by incoming ions through both direct and indirect (δ ray) events. At any designated (ray traced) target point within the vehicle, the model accepts the differential flux spectrum of Galactic Cosmic Rays (GCRs) and/or trapped protons at LEO as input. On a desktop PC, the response function of TEPC for each ion in the GCR/trapped field is computed at the average rate of 30 s/ion. The ionizing radiation environment at LEO is represented by O’Neill’s GCR model (2004), covering charged particles in the 1 ? Z ? 28 range. O’Neill’s free space GCR model is coupled with the Langley Research Center (LaRC) angular dependent geomagnetic cutoff model to compute the transmission coefficient in LEO. The trapped proton environment is represented by a LaRC developed time dependent procedure which couples the AP8MIN/AP8MAX, Deep River Neutron Monitor (DRNM) and F10.7 solar radio frequency measurements. The albedo neutron environment is represented by the extrapolation of the Atmospheric Ionizing Radiation (AIR) measurements. The charged particle transport calculations correlated with STS 51 and 114 flights are accomplished by using the most recent version (2005) of the LaRC deterministic High charge (Z) and Energy TRaNsport (HZETRN) code. We present the correlations between the TEPC model predictions (response function) and TEPC measured differential/integral spectra in the lineal energy (y) domain for both GCR and trapped protons, with the conclusion that the model correctly accounts for the increase in flux at low y values where energetic ions are the primary contributor. We further discuss that, even with the incorporation of angular dependency in the cutoffs, comparison of the GCR differential/integral flux between STS 51 and 114 TEPC measured data and current calculations indicates that there still exists an underestimation by the simulations at low to mid range y values. This underestimation is partly related the exclusion of the secondary pion particle production from the current version of HZETRN.     

Experimental data and analysis of the October 2003 Forbush decrease

On October 28, 2003 an Earthward-directed coronal mass ejection (CME) was observed from SOHO/LASCO imagery in conjunction with an X17 solar flare. The CME, traveling at nearly 2000 km/s, impacted the Earth on October 29, 2003 causing ground-based particle detectors to register a counting rate drop known as a Forbush decrease. The CME was not only responsible for affecting the rate of cosmic rays, but also caused anisotropies in their direction of incidence. Data from Project GRAND, an array of proportional wire chambers which detects secondary muons, are presented during the time of this Forbush decrease.     

Impact induced plasma during a cometary fly-by

GIOTTO, the probe which is presently developed by the European Space Agency, will encounter comet Halley in March 1986 with a relative velocity of 69 km/s. The fore section of the surface will be submitted to the bombardment of dust grains and neutral molecules in the final phase of the mission, like that of an Earth orbiter during atmospheric re-entry. These particles have a kinetic energy of 24 eV per a.m.u.; they produce secondary ions and electrons which form a plasma cloud around the body and control the electric potential of its surface. This paper is a review of the work which has been performed on the subject by dedicated study groups; the purpose of their action was to gather information and produce new findings which might have an influence on the design of the spacecraft and help in the interpretation of the data collected by the scientific payload.

The effect of impact induced plasma may already be significant at 10⁵ km from the comet nucleus; at a distance of 1000 km the flux of ions and electrons produced by cometary dust and neutrals will possibly exceed that of the ambient plasma by more than three orders of magnitude. It is expected that the spacecraft surface potential will be positive and will reach at least a few tens of volts; coating the leading surface of the spacecraft with a thin layer of gold or silver will help reducing the emission of ions from neutral gas. Computer simulation models are used to predict the structure of the charged particle density distribution in the vicinity of the surface. Effects associated with the wake and differential charging are also discussed. The significance of these results is conditioned by the validity of the models and the largest source of uncertainty seems to be associated with the plasma generated by dust impact.     

An engineering model of Titan surface winds for Dragonfly landed operations

Winds near the ground on Titan for the Dragonfly landing site (near Selk crater, 10°N) for the mid-2030s (Titan late southern summer, L_s ~ 310°) are estimated for mission design purposes. Prevailing winds due to the global circulation are typically 0.5 m/s, and do not exceed 1 m/s. Local terrain-induced flows such as slope winds appear to be similarly capped at 1 m/s. At various landing sites and times, these two contributions will vectorially combine to yield steady winds (for part of a Titan day, Tsol) of up to 2.0 m/s, but typically less – the slope wind component will be small in the mid-morning. In early afternoon, as on Earth and Mars, solar-driven convection in the planetary boundary layer will cause wind fluctuations of the order of 0.1 m/s, varying with a typical timescale of ~1000 s. Occasionally this convection organizes into coherent ‘dust devil’ vortices: detectable vortices with speeds of 1 m/s are predicted about once per Titan day. We have introduced the convective velocity scale combined with the advection time of PBL cells as a metric to derive the frequency of occurrence of gusts associated with convective vortices (‘dust devils’). Maximum possible vortex winds on Titan of 2.8 m/s may be expected only once per 40 Tsols, and define the maximum wind (4.8 m/s at 10 m height) that Dragonfly must tolerate without damage. The applicability of different wind combinations, scaled to the height of relevant Dragonfly components above the ground (e.g. the maximum corresponds to 3.9 m/s at 1.3 m height) by a logarithmic wind profile, to Dragonfly design and operations are discussed.     

Rocket observation of the ultraviolet spectrum of comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on 26 February 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 × 10²⁹ s⁻¹ and the volume mixing ratio of CO to H₂O is 21%. The predicted brightness distribution from a radial outflow model with H₂O and CO as parent molecules are in accordance with the measured spatial profiles of OI and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker CI emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3% of the water production rate is included in the model.     

New flare model using recent measurements of the solar ultraviolet irradiance

The solar photon output from the Sun, which was once thought to be constant, varies considerably over time scales from seconds during solar flares to years due to the solar cycle. This is especially true in the wavelengths shorter than 190 nm. These variations cause significant deviations in the Earth and space environment on similar time scales, which then affects many things including satellite drag, radio communications, atmospheric densities and composition of particular atoms, molecules, and ions of Earth and other planets, as well as the accuracy in the Global Positioning System (GPS). The Flare Irradiance Spectral Model (FISM) is an empirical model that estimates the solar irradiance at wavelengths from 0.1 to 190 nm at 1 nm resolution with a time cadence of 60 s. This is a high enough temporal resolution to model variations due to solar flares, for which few accurate measurements at these wavelengths exist. This model also captures variations on the longer time scales of solar rotation (days) and solar cycle (years). Daily average proxies used are the 0–4 nm irradiance, the Mg II c/w, F10.7, as well as the 1 nm bins centered at 30.5 nm, 121.5 (Lyman Alpha), and 36.5 nm. The GOES 0.1–0.8 nm irradiance is used as the flare proxy. The FISM algorithms are given, and results and comparisons are shown that demonstrate the FISM estimations agree within the stated uncertainties to the various measurements of the solar Vacuum Ultraviolet (VUV) irradiance.     

On the production of highest energy solar protons at 20 January 2005

On January 20, 2005, 7:02–7:05 UT the Aragats Multidirectional Muon Monitor (AMMM) located at 3200 m a.s.l. registered enhancement of the high energy secondary muon flux (threshold ∼5 GeV). The enhancement, lasting for 3 min, has statistical significance of ∼4σ and is related to the X7.1 flare seen by the GOES, and very fast (>2500 km/s) CME seen by SOHO, and the Ground Level Enhancements (GLE) #69 detected by the world-wide network of neutron monitors and muon detectors. The energetic and temporal characteristics of the muon signal from the AMMM are compared with the characteristics of other monitors located at the Aragats Space-Environmental Center (ASEC) and with other neutron and muon detectors. Since secondary muons with energies >5 GeV are corresponding to solar proton primaries with energies 20–30 GeV we conclude that in the episode of the particle acceleration at 7:02–7:05 UT 20 January 2005 solar protons were accelerated up to energies in excess of 20 GeV.     

Collection of cometary dust

Rendezvous Missions to Comets lead to low velocities at the nucleus of the comet. The resulting impact velocity of the cometary dust on a target will range between 10 and 400 m/s. The dust particle which impacts on a target can be collected for a subsequent in-situ analysis.

The collection efficiency of a target depends in addition to obvious geometrical conditions upon the surface of the target. The surface characteristics can be divided into two groups:

• “dirty” surfaces, covered with silicate or hydrocarbon compounds (for example vacuum grease),

• “clean” surfaces, like gold (with additional sputtering).

This paper deals with the experimental and theoretical investigation of the collection efficiency of “clean” targets. Laboratory experiments are described which were conducted at the Technische Universität München, Lehrstuhl für Raumfahrttechnik, and the Max-Planck-Institut für Kernphysik, Heidelberg. In both experiments an electromagnetic accelerator is used to accelerate different types of dust in vacuum to velocities between 10 and 400 m/s.

The target is then examined under the microscope and a secondary ion mass spectrometer (which is a model of the laboratory carried on board of the spacecraft for “in situ” analysis). The adhesion of the dust grains at the target is evaluated experimentally in an ultracentrifuge.     

大气中子实时计算模式

为实时评估0~100km高度范围内的大气中子全球分布,对宇宙线在地磁场和大气中的传输过程进行了分析.利用蒙特卡罗方法工具包Geant4,预先计算不同能量的粒子在大气层中产生的次级粒子能谱分布,形成大气次级粒子数据库,并与相关模型进行对比,验证了该数据库的有效性和可靠性.以实测或预报的空间环境参数作为输入,计算同步轨道银河宇宙线和太阳质子事件能谱以及100km高度上的地磁垂直截止刚度,最终得到大气层顶上的粒子能谱.通过对大气次级粒子数据库的线性插值,实现1h分辨率的大气中子能谱和辐射剂量全球分布的实时计算.