2004年3月13日TC-1和Cluster卫星联合观测的磁通量传输事件

分析了2004年3月13日12:15到12:25UT期间TC-1和Cluster卫星簇的磁通门磁力计(FGM)和电子/电流试验仪(PEACE)的联合观测数据.在此期间,TC-1卫星位于日下点以南的磁层顶附近的磁鞘中,并在12:19UT左右观测到了一个典型的先正后负的磁鞘磁通量传输事件(FTE);而Cluster卫星簇位于北半球日侧高纬磁层项附近,并于12:23UT左右穿出磁层顶进入磁鞘,且在12:21 UT左右也观测到了一个典型的先正后负的磁层FTE.比较分析发现此两个FTE具有类似的磁场结构和等离子体特征,可能是同一个北向运动的FTE先后被TC-1和Cluster卫星观测到.利用Cluster 4颗卫星的多点同时观测数据,采用最小方向微分法和时空微分方法,推断Cluster卫星观测的这个FTE是尺度大小约为1.21Re的准二维结构,其运动方向为东北方向,与Cooling模型预测方向基本一致.利用Cooling模型的预测,推算了TC-1卫星在12:19UT观测的FTE的运动速度和尺度,进而得出随着通量管的极向运动,其速度和尺度均有所增加.     

Phase separated membrane bioreactor: results from model system studies.

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestrial [correction of terrestial] simulation.     

Calibration techniques for magnetometers implementing on-board de-spinning algorithms

The Fluxgate Magnetometer experiments on-board the European Space Agency’s four spacecraft Cluster Mission have the capability to store sampled magnetic field vectors in the instrument memory, either as a full resolution ‘event capture’ or as spin-resolution vectors transformed into a non-spinning co-ordinate system (de-spun). The latter capability has ensured a dataset is available which extends the partial orbital coverage achieved during nominal operations in the first years of operation. The on-board de-spin is achieved using a Walsh function with Haar coefficients and allows for up to 27 h additional data per non-coverage interval. A number of commissioning orbits were used to verify the accuracy of data collected by the de-spin mode, whereby individual spacecraft were operated separately in a number of standard normal sampling and de-spin mode combinations. Up to the present time, this data has not been available to the Cluster community. We present results here comparing the performance of the on-board de-spin algorithm versus the normal sampling modes over a number of boundary layer crossings, describe the techniques used for calibration and timeline recovery, and outline the context in which the data may be usable in future studies.     

Evolution of a phase separated gravity independent bioreactor.

The evolution of a phase-separated gravity-independent bioreactor is described. The initial prototype, a zero head-space manifold silicone membrane based reactor, maintained large diffusional resistances. Obtaining oxygen transfer rates needed to support carbon-recycling aerobic microbes is impossible if large resistances are maintained. Next generation designs (Mark I and II) mimic heat exchanger design to promote turbulence at the tubing-liquid interface, thereby reducing liquid and gas side diffusional resistances. While oxygen transfer rates increased by a factor of ten, liquid channeling prevented further increases. To overcome these problems, a Mark III reactor was developed which maintains inverted phases, i.e., media flows inside the silicone tubing, oxygen gas is applied external to the tubing. This enhances design through changes in gas side driving force concentration and liquid side turbulence levels. Combining an applied external pressure of four atmospheres with increased Reynolds numbers resulted in oxygen transfer intensities of 232 mmol O2/l/h (1000 times greater than first prototype and comparable to a conventional fermenter). A 1.0 liter Mark III reactor can potentially deliver oxygen supplies necessary to support cell cultures needed to recycle a 10 astronaut carbon load continuously.     

Development of a CELSS bioreactor: oxygen transfer and micromixing in parabolic flight.

The gas exchange portion of a phase-separated loop bioreactor was tested with respect to oxygen mass transfer and micromixing in accelerations of 0.01g, 1g, and 2g. A plot of the overall mass transfer coefficient versus gravity indicates the rate of oxygen transfer does not change as a function of acceleration. Also, it was determined that the micromixing did not exhibit significant changes in the various gravitational fields. These observations indicate the loop bioreactor should function independent of acceleration.     

Multi-point observations and modeling of subauroral polarization streams (SAPS) and double-peak subauroral ion drifts (DSAIDs): A case study

While subauroral polarization streams (SAPS) are well recognized as representatively one of the most important features of magnetosphere-ionosphere (M-I) coupling processes in the subauroral region, the double-peak subauroral ion drifts (DSAIDs) is a newly recognized ionospheric phenomenon, categorized as a subset of subauroral ion drifts (SAIDs). In this study, we investigate both SAPS and DSAIDs that appear during the storm main phase of the 17 March 2015 event through a combination of multi-point observations and numerical simulations. We find that when SAPS/DSAIDs are observed by the DMSP spacecraft near the dusk subauroral region, strong electric fields are detected minutes later by the Van Allen Probes almost in the same conjugate region near the equatorial plane. Numerical simulations are carried out not only to reveal the global context and dynamic evolution of the SAPS in both the magnetospheric and ionospheric systems, but also to aid the understanding of the effect of conductance on the DSAIDs. Our results confirm that SAPS are indeed associated with Region 2 field-aligned currents (FACs) flowing into the low conductance region. On the other hand, the DSAIDs may be related to the double-conductance-trough in the subauroral region.     

Mirror structures in the magnetosheath: 3D structures on plane waves

Mirror mode oscillations are often observed in the magnetosheath. According to linear, kinetic theory, these waves do not propagate in the plasma rest frame and posses a linear polarisation. However, observations of these waves show them to exhibit a non-planar polarisation. Using data collected by the AMPTE-UKS satellite on 21^st September, 1984, this paper investigates the nature of these waves using the variance analysis technique to determine the polarisation and maximum/minimum variance directions. The results show that the individual oscillations do indeed posses non-planar characteristics and the variation in the maximum/minimum variance directions indicates that these oscillations are in fact 3D structures propagating with the plasma rather than a 2D plane wave.     

Human exploration of near earth asteroids: Mission analysis for chemical and electric propulsion

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future.     

Evaluation of substorm models with Cluster observations of plasma flow reversal in the magnetotail

We evaluate two prevailing substorm models with an event of plasma flow reversal from tailward to Earthward detected by Cluster at the downstream distance of ∼19 R_E in the magnetotail during a substorm on August 22, 2001. We use the unique capability of Cluster measurements in determining gradients to examine the associated current density, Lorentz force, and current dissipation/dynamo term. In association with plasma flow reversal, it is found that (1) there was no clear quadrupole magnetic perturbation signature, (2) the x-component of the Lorentz force did not change sign, (3) the y-component of the product of the current density and the electric field was occasionally negative indicative of a dynamo effect, and (4) the timing sequence of flow reversal from the Cluster configuration did not match tailward motion of a single plasma flow source. These observations are consistent with the near-Earth initiation model for substorms with multiple current disruption sites moving progressively tailward near the late stage of substorm expansion.     

Dream project: Applications of earth observations to disaster risk management

The field of disaster risk management is relatively new and takes a structured approach to managing uncertainty related to the threat of natural and man-made disasters. Disaster risk management consists primarily of risk assessment and the development of strategies to mitigate disaster risk. This paper will discuss how increasing both Earth observation data and information technology capabilities can contribute to disaster risk management, particularly in Belize. The paper presents the results and recommendations of a project conducted by an international and interdisciplinary team of experts at the 2009 session of the International Space University in NASA Ames Research Center (California, USA). The aim is to explore the combination of current, planned and potential space-aided, airborne, and ground-based Earth observation tools, the emergence of powerful new web-based and mobile data management tools, and how this combination can support and improve the emerging field of disaster risk management. The starting point of the project was the World Bank’s Comprehensive Approach to Probabilistic Risk Assessment (CAPRA) program, focused in Central America. This program was used as a test bed to analyze current space technologies used in risk management and develop new strategies and tools to be applied in other regions around the world.