The Planets and Titan Observed by ISO

Infrared spectroscopic observations of planets and Saturn's satellite Titan with the Infrared Space Observatory led to many significant discoveries that improved our understanding on the formation, physics and chemistry of these objects. The prime results achieved by ISO are: (1) a new and consistent determination of the D/H ratios on the giant planets and Titan; (2) the first precise measurement of the ¹⁵N/¹⁴N ratio in Jupiter, a valuable indicator of the protosolar nitrogen isotopic ratio; (3) the first detection of an external oxygen flux for all giant planets and Titan; (4) the first detection of some stratospheric hydrocarbons (CH₃, C₂H₄, CH₃C₂H, C₄H₂, C₆H₆); (5) the first detection of tropospheric water in Saturn; (6) the tentative detection of carbonate minerals on Mars; (7) the first thermal lightcurve of Pluto. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

A Class of TVD Type Combined Numerical Scheme for MHD Equations With a Survey About Numerical Methods in Solar Wind Simulations

It has been believed that three-dimensional, numerical, magnetohydrodynamic (MHD) modelling must play a crucial role in a seamless forecasting system. This system refers to space weather originating on the sun; propagation of disturbances through the solar wind and interplanetary magnetic field (IMF), and thence, transmission into the magnetosphere, ionosphere, and thermosphere. This role comes as no surprise to numerical modelers that participate in the numerical modelling of atmospheric environments as well as the meteorological conditions at Earth. Space scientists have paid great attention to operational numerical space weather prediction models. To this purpose practical progress has been made in the past years. Here first is reviewed the progress of the numerical methods in solar wind modelling. Then, based on our discussion, a new numerical scheme of total variation diminishing (TVD) type for magnetohydrodynamic equations in spherical coordinates is proposed by taking into account convergence, stability and resolution. This new MHD model is established by solving the fluid equations of MHD system with a modified Lax-Friedrichs scheme and the magnetic induction equations with MacCormack II scheme for the purpose of developing a combined scheme of quick convergence as well as of TVD property. To verify the validation of the scheme, the propagation of one-dimensional MHD fast and slow shock problem is discussed with the numerical results conforming to the existing results obtained by the piece-wise parabolic method (PPM). Finally, some conclusions are made. This revised version was published online in August 2006 with corrections to the Cover Date.     

Discrete energy release in microwave emission in the preflare stage

Examples of solar microwave precursors and estimates of their energetic characteristics are discussed based on spectral investigations of the preflare activity.     

Design-to-Cost Applied Within an Integrated System Model

In an environment of declining financial budgets for space projects, new approaches - such as Design-To-Cost - are being implemented to improve today's satellite design processes. Using an example of a current mission (the power subsystem of the Solar Probe spacecraft) under study at NASA's Jet Propulsion Laboratory, the main part of the paper discusses an Integrated System Model (structured into a performance model, a cost model, and an effectiveness model) that is part of a model-based design process used to perform cost-effectiveness trades. A simulation tool is used during the first step to size the components of the power subsystem, and then simulate its performance during operation. The determined dimensions are transferred into an EXCEL^TM-spreadsheet and linked to the components' costs. With a cost accounting tool that combines cost estimating relationships with the Work Breakdown Structure of the power subsystem, the life-cycle cost of each alternative design concept is computed. To determine the cost-risk of the different design alternatives for each component, cost probability distributions are introduced. By performing Monte-Carlo simulations, cost sensitivities are revealed. In the next step of the trade study process, the effectiveness of the alternatives is analyzed. Having determined cost and effectiveness, estimates can be made for where the different alternatives lie in the design space. The last part of the paper identifies the main drivers for the spacecraft's performance and cost. Finally it is shown how the mission design benefited from the Integrated System Model and from the application of Design-To-Cost.     

Properties of Interplanetary Coronal Mass Ejections

Interplanetary coronal mass ejections (ICMEs) originating from closed field regions on the Sun are the most energetic phenomenon in the heliosphere. They cause intense geomagnetic storms and drive fast mode shocks that accelerate charged particles. ICMEs are the interplanetary manifestations of CMEs typically remote-sensed by coronagraphs. This paper summarizes the observational properties of ICMEs with reference to the ordinary solar wind and the progenitor CMEs.     

一种定量建立主题数据库的算法

本文利用企业模型中的企业活动与实体之间的关系给出了实体组之间的相关系数定义，在此基础上，给出了实体组的分组算法，从而应可以根据主要数据库分划标准把实体划分成实体大组，形成主题数据库。     

First results from the LUCID-Timepix spacecraft payload onboard the TechDemoSat-1 satellite in Low Earth Orbit

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) is a payload onboard the satellite TechDemoSat-1, used to study the radiation environment in Low Earth Orbit ($～$635?km). LUCID operated from 2014 to 2017, collecting over 2.1 million frames of radiation data from its five Timepix detectors on board. LUCID is one of the first uses of the Timepix detector technology in open space, with the data providing useful insight into the performance of this technology in new environments. It provides high-sensitivity imaging measurements of the mixed radiation field, with a wide dynamic range in terms of spectral response, particle type and direction. The data has been analysed using computing resources provided by GridPP, with a new machine learning algorithm that uses the Tensorflow framework. This algorithm provides a new approach to processing Medipix data, using a training set of human labelled tracks, providing greater particle classification accuracy than other algorithms. For managing the LUCID data, we have developed an online platform called Timepix Analysis Platform at School (TAPAS). This provides a swift and simple way for users to analyse data that they collect using Timepix detectors from both LUCID and other experiments. We also present some possible future uses of the LUCID data and Medipix detectors in space.     

面向深空探测的电磁帆推进技术研究进展

电磁帆是一类利用太阳风驱动的无工质或少工质新型推进技术,在需要推力器长时间工作的深空探测任务中具有非常广阔的应用前景。首先介绍了电磁帆的基本概念和主要分类,其次分别介绍了电帆、纯磁帆和磁等离子体帆三类推进方式的系统组成和工作原理,重点介绍了各自的研究现状,并梳理出了相关关键技术,同时介绍了等离子体磁罩技术。最后对电磁帆推进技术研究进展进行了总结,为国内开展此方面研究提供了研究方向和发展思路。     

Comparison of observed ionospheric vertical TEC over the sea in Indian region with IRI-2016 model

The vertical ionospheric TEC values obtained from GAGAN grid based ionospheric delay correction values over the sea in the Indian equatorial region have been compared with the corresponding values derived from the International Reference Ionosphere model, IRI-2016. The objective of this work is to study the deviation of the vertical TEC derived from the IRI model from ground truths over the sea for different conditions. This will serve the basic intention of assessing the candidature of the IRI model as an alternative ionospheric correction model in navigation receivers in terms of accuracy. We have chosen different solar activity periods, seasons, geomagnetic conditions, locations etc. for our comparison and analysis. The TEC values by the IRI-2016 were compared with the actual measured values for the given conditions and errors were obtained. The measured vertical TEC values at the ionospheric grid points were derived from the GAGAN broadcast ionospheric delay data and used as reference. The IRI model with standard internal functions was used in estimating the TEC at the same ionospheric grid points. The errors in the model derived values are statistically analysed. Broadly, the results show that, for the Indian sector over the sea, the IRI model performs better on quiet days in off equatorial regions, particularly in the northern region. The overall performance degrades for other conditions with the model generally underestimating the true TEC values and most severely in the equatorial region. The performance is worst in this region for the disturbed days of the equinoctial period. The comparison study is also done with the TEC data measured directly by dual frequency GPS receivers. The results were found to be in general agreement with those obtained by comparing the model with GAGAN broadcast data as reference. This study will be useful in considering the IRI-2016 model for real time estimates of TEC as an alternative to the current parametric model in a satellite navigation receiver in absence of other options.     

Non-stationarity and cross-correlation effects in the MHD solar activity

The analysis of turbulent processes in sunspots and pores which are self-organizing long-lived magnetic structures is a complicated and not yet solved problem. The present work focuses on studying such magneto-hydrodynamic (MHD) formations on the basis of flicker-noise spectroscopy using a new method of multi-parametric analysis. The non-stationarity and cross-correlation effects taking place in solar activity dynamics are considered. The calculated maximum values of non-stationarity factor may become precursors of significant restructuring in solar magnetic activity. The introduced cross-correlation functions enable us to judge synchronization effects between the signals of various solar activity indicators registered simultaneously.