Plasmas in the earth's magnetotail

An overview of the general characteristics of plasmas within the Earth's magnetotail and its environs is presented. Present knowledge of the plasmas within these regions as gained via in situ measurements provides the general theme, although observations of magnetic fields, energetic particles and plasma waves are included in the discussion. Primary plasma regimes in the magnetotail are the plasma sheet, its boundary layer, the magnetotail lobes, the boundary layer at the magnetopause and the distant magnetotail. Although great progress in our understanding of these regions is evident in the literature of the past several years, many of their features remain as exciting enigmas to be resolved by future observational and theoretical investigation.     

The measured radiation environment within Spacelabs 1 and 2 and comparison with predictions

To measure the radiation environment in the Spacelab (SL) module and on the pallet, a set of passive and active radiation detectors was flown as part of the Verification Flight Instrumentation (VFI). SL 1 carried 4 passive and 2 active detector packages which, with the data from the 26 passive detectors of Experiment INS006, provided a comprehensive survey of the radiation environment within the spacecraft. SL 2 carried 2 passive VFI units on the pallet. Thermoluminescent dosimeters (TLDs) measured the low linear energy transfer (LET) dose component; the HZE fluence and LET spectra were mapped with CR-39 track detectors; thermal and epithermal neutrons were measured with the use of fission foils; metal samples analyzed by gamma ray spectroscopy measured low levels of several activation lines. The TLDs registered from 97 to 143 mrad in the SL 1 module. Dose equivalents of 330±70 mrem in the SL 1 module and 537±37 mrem on the SL 2 pallet were measured. The active units in the SL 1 module each contained an integrating tissue-equivalent ion chamber and two differently-shielded xenon-filled proportional counters. The ion chambers accumulated 125 and 128 mrads for the mission with 17 and 12 mrads accumulated during passages through the South Atlantic Anomaly (SAA). The proportional counter rates (1 cps at sea level) were 100 cps in the middle of the SAA (mostly protons), 35 cps at large geomagnetic latitudes (cosmic rays) and 100 cps in the South Horn of the electron belts (mostly bremsstrahlung). Detailed results of the measurements and comparison with calculated values are described.     

Atmospheric Aerosol and Cloud Condensation Nuclei Formation: A Possible Influence of Cosmic Rays?

A physical mechanism which may have a potential to connect climate with cosmic rays (CR) involves aerosol particle formation by CR generated atmospheric ions followed by new particle growth. Only grown particles can scatter sunlight efficiently and can eventually act as cloud condensation nuclei (CCN) and thereby may influence climate. Moreover grown particles live longer as they are less rapidly scavenged by pre-existing larger particles. The present paper discusses aerosol particle formation and growth in the light of new measurements recently made by our MPIK Heidelberg group. Emphasis is placed upon the upper troposphere where very low temperatures tend to facilitate new particle formation by nucleation. The new measurements include: laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, and atmospheric measurements of the powerful nucleating gas H₂SO₄ and its precursor SO₂. The discussion also addresses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere new aerosol formation by CR generated ions is a frequent process with relatively large rates. However new particle formation by homogeneous nucleation (HONU) which is not related to CR also seems to be efficient. The bottleneck in the formation of upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is not nucleation but growth of small particles. Our recent upper troposphere SO₂ measurements suggest that particle growth by gaseous sulphuric acid condensation is at least occasionally efficient. If so CR mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere.     

Periodic or random acceleration in solar flares?

The issue whether acceleration and injection of electron beams is coherently modulated by a single quasi-periodic source, or whether the injection is driven by a stochastic process in time or (eventually fragmented) in space, is investigated by menas of a periodicity analysis of metric type III bursts.We analyze 260 continuous type III groups observed byIkarus (ETH Zurich) in the frequency range of 100–500 MHz during 359 solar flares with simultaneous 25 keV hard X-ray emission, in the years 1980–1983. Pulse periods have been measured between 0.5 and 10 s, and can be described by an exponential distribution, i.e.N(P) e ^–P/1.0s. We measure the mean periodP and its standard deviation p in each type III group, and quantify the degree of periodicity by the dimensionless parameter p/P. The representative sample of 260 type III burst groups shows a mean periodicity of p/P=0.37±0.12, while Monte-Carlo simulations of an equivalent set of truly random time series show a distinctly different value of p/P=0.93±0.26. This result suggests that the injection of electron beams is periodically modulated by a particle acceleration source which is either compact or has a global organization on a time scale of seconds.     

Simulating clefts in pumpkin balloons

The geometry of a large axisymmetric balloon with positive differential pressure, such as a sphere, leads to very high film stresses. These stresses can be significantly reduced by using a tendon re-enforced lobed pumpkin-like shape. A number of schemes have been proposed to achieve a cyclically symmetric pumpkin shape, including the constant bulge angle (CBA) design, the constant bulge radius (CBR) design, CBA/CBR hybrids, and NASA’s recent constant stress (CS) design. Utilizing a hybrid CBA/CBR pumpkin design, Flight 555-NT in June 2006 formed an S-cleft and was unable to fully deploy. In order to better understand the S-cleft phenomenon, a series of inflation tests involving four 27-m diameter 200-gore pumpkin balloons were conducted in 2007. One of the test vehicles was a 1/3-scale mockup of the Flight 555-NT balloon. Using an inflation procedure intended to mimic ascent, the 1/3-scale mockup developed an S-cleft feature strikingly similar to the one observed in Flight 555-NT. Our analysis of the 1/3-scale mockup found it to be unstable. We compute asymmetric equilibrium configurations of this balloon, including shapes with an S-cleft feature.     

未来10年中东地区的机队及维修进展

据美国航空周刊MRO Prospector提供的数据,2008年中东地区航空维修市场总支出约为22.1亿美元,其中与宽体飞机相关的维修支出约占总数的68.2%.随着中东地区航空公司机队规模的不断壮大,到2018年该地区的民用航空维修支出将增长56%,达到34.4亿美元.而且宽体飞机将会由2008年的400架增至2018年的668架,增幅达67%,维修支出的比例也将升高为68.5%.     

从竞争到合作

大约4年前,加拿大航空技术公司(ACTS)与铬合金公司结为战略合作伙伴,在CF34发动机的维修中采用由铬合金公司生产的PMA件,以减少大修成本.     

Impact of Jason-2/T2L2 Ultra-Stable-Oscillator Frequency Model on DORIS stations coordinates and Earth Orientation Parameters

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is a tracking technique based on a one-way ground to space Doppler link. For Low Earth Orbit (LEO) satellites, DORIS shows a robust capability in terms of data coverage and availability, due to a wide and well-distributed ground network, where data are made available by the International Doris Service (IDS). However, systematic errors remain in the DORIS data, such as instabilities of the on-board clock due to radiation encountered in space, which limit the accurate determination of station positions.The DORIS on-board clock frequency stability is degraded by the increased radiation found in the region of the South Atlantic Anomaly (SAA) and has been shown to degrade station position estimation. This paper introduces a new model correction to the DORIS data for the frequency of the Jason-2 Ultra Stable Oscillator (USO), derived from the Time Transfer by Laser Link (T2L2) experiment (Belli and Exertier, 2018). We show that a multi-satellite DORIS solution including this T2L2-corrected data applied to the frequency modelling for The DORIS data, improves the estimation of station coordinates. We show the tie residuals with respect to collocated GPS stations are improved by several millimeters. We also demonstrate that the 117-day (Jason-2) draconitic signal in the geophysical parameters is reduced, implying that the origin of this signal is not just solar radiation pressure mis-modeling, but also radiation-induced clock perturbations on the Jason-2 DORIS Ultra-Stable-Oscillator (USO). Finally we demonstrate through comparisons with the International Earth Rotations and Reference Systems Service (IERS) C04 series for Earth Orientation Parameters (EOP), that the estimation of EOP is improved in both a Jason-2 DORIS-only and a multi-satellite DORIS solution for EOP.     

Cosmic-Ray Modulation in the Heliosphere A Phenomenological Study

The heliospheric cosmic-ray network–Pioneer 10/11, Voyager 1/2, Ulysses and IMP 8 have provided detailed observations of galactic and anomalous cosmic rays over a period of time that now exceeds 25 years and extends to heliocentric distances beyond 65 AU. These data, when compared over consecutive 11 year solar cycles, clearly establishes the existence of a 22-year cosmic ray modulation cycle that is dominated by the 11-year solar activity cycle but is strongly influenced by gradient and curvature drifts in association with the tilt of the heliospheric neutral current sheet as well as the mediation of the enhanced magnetic turbulence above the solar poles. Over successive solar minima these effects manifest themselves in the remarkable differences in the energetic particle time histories, in the magnitude and sign of the radial and latitudinal intensity gradients and in the changes in the energy spectra of anomalous cosmic rays as a function of heliocentric distance.From solar minimum to solar maximum the long term modulation is principally a combination of two solar related phenomena, the cumulative effect of long-lived global merged interaction regions (GMIRs) and gradient and curvature drifts in the interplanetary magnetic field. For the periods when positive ions flow in over the solar poles and out along the heliospheric current sheet, the modulation of ions is dominated by GMIRs. When this flow pattern is reversed it is found that drifts are an important but not dominant factor for cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity R, heliolatitude and heliocentric distance. Over a single solar cycle these conclusions are confirmed at 1 AU by comparing the relative modulation of cosmic-ray helium nuclei and electrons.     

Optimization of the tether-assisted return mission of a guided re-entry capsule

This paper presents the mission analysis of a tether-assisted payload retrieval from the International Space Station (ISS). The objective is to assess all relevant phases of such a mission in order to allow a comparison with a conventional mission employing a propulsive deorbitation. The controlled tether deployment procedure and the guided return flight of the released re-entry capsule are optimized. A preferable deployment strategy is identified that allows for favorable entry conditions and low flight loads. The optimal deployment trajectories serve as a basis for an optimal dynamic regulator. This approach is extended towards an adaptive concept, where artificial neural networks are applied to deployment control. For the guidance of the capsule a predictive concept is proposed that is based on the optimal re-entry trajectories identified previously. By applying these concepts, the attainable landing accuracy during return amounts to an average of 5 km, and the application of the tether system exhibits overall system mass advantages. This demonstrates that the tether-assisted return mission is a competitive alternative.