Reconstituting the US space programme

This response to Alex Roland's article, ‘Priorities in space for the USA’, argues that his analysis and conclusions are based on shaky historical evidence. Professor Roland's interpretation of NASA's priorities since 1959 is challenged, and it is pointed out that the manned spaceflight programme has widespread support in the USA. The most important issue, raised by the article but not treated extensively enough, is whether the pursuit of the widely accepted emphasis on manned spaceflight is a large-scale societal mistake.     

US and Soviet planetary exploration The next step is Mars, together

Soviet General Secretary Gorbachev has proposed a joint US-Soviet programme to explore the planet Mars. The authors argue that there is considerable advantage to be gained from such a programme for both countries and for all nations on Earth. They trace the history of the US and Soviet space programmes and of cooperation between the two nations, focusing particularly on activities relating to Mars. Robotic Mars exploration is already technically possible and could take place in the 1990s, and a first step towards manned exploration could be the writing of a development and flight plan aiming for the first decade of the 21st century.     

Ground based ISS payload microgravity disturbance assessments

In order to verify that the International Space Station (ISS) payload facility racks do not disturb the microgravity environment of neighboring facility racks and that the facility science operations are not compromised, a testing and analytical verification process must be followed. Currently no facility racks have taken this process from start to finish. The authors are participants in implementing this process for the NASA Glenn Research Center (GRC) Fluids and Combustion Facility (FCF). To address the testing part of the verification process, the Microgravity Emissions Laboratory (MEL) was developed at GRC. The MEL is a 6 degree of freedom inertial measurement system capable of characterizing inertial response forces (emissions) of components, sub-rack payloads, or rack-level payloads down to 10(-7) g's. The inertial force output data, generated from the steady state or transient operations of the test articles, are utilized in analytical simulations to predict the on-orbit vibratory environment at specific science or rack interface locations. Once the facility payload rack and disturbers are properly modeled an assessment can be made as to whether required microgravity levels are achieved. The modeling is utilized to develop microgravity predictions which lead to the development of microgravity sensitive ISS experiment operations once on-orbit. The on-orbit measurements will be verified by use of the NASA GRC Space Acceleration Measurement System (SAMS). The major topics to be addressed in this paper are: (1) Microgravity Requirements, (2) Microgravity Disturbers, (3) MEL Testing, (4) Disturbance Control, (5) Microgravity Control Process, and (6) On-Orbit Predictions and Verification.     

Highlights about the performances of storm-time TEC modelling techniques for low/equatorial and mid-latitude locations

A statistical evaluation of storm-time total electron content (TEC) modelling techniques over various latitudes of the African sector and surrounding areas is presented. The source of observational TEC data used in this study is the Global Navigation Satellite Systems (GNSS), specifically the Global Positioning Systems (GPS) receiver networks. For each selected receiver station, three different storm-time models based on empirical orthogonal functions (EOF) analysis, non-linear regression analysis (NLRA) and Artificial neural networks (ANN), were implemented. Storm-time GPS TEC data used for both development and validation of the models was selected based on the storm criterion of $\mathit{Dst}?-50$ nT or $K_p?4$ to take into account both coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs) driven storms, respectively. To make an independent test of the models, storm periods considered for validation were excluded from datasets used during the implementation of the models and results are compared with observations, monthly median values, and International Reference Ionosphere (IRI-2016) predictions. Considering GPS TEC as reference, a statistical analysis performed over six storm periods reserved for validation revealed that ANN model is about 10%, 26%, and 58% more accurate than EOF, NLRA, and IRI models, respectively. It was further found that, EOF model performs 15%, and 44% better than NLRA, and IRI models, respectively, while NLRA is 25% better than IRI. On the other hand, results are also discussed referring to the background ionosphere represented by monthly median TEC (MM TEC) and statistics are provided. Moreover, strengths and weaknesses of each model are highlighted.     

Relative equilibria in quasi-homogeneous planar three body problems

In this paper we find the families of relative equilibria for the three body problem in the plane, when the interaction between the bodies is given by a quasi-homogeneous potential. The number of the relative equilibria depends on the values of the masses and on the size of the system, measured by the moment of inertia.     

Experimental study of a flush wall scramjet combustor equipped with strut/wall fuel injection

In this study a flush wall scramjet combustor is tested in a supersonic incoming air flow with the Mach number of 3 which is generated by an air vitiation heater producing the stagnation temperature of 1505 K. Using liquid kerosene as the fuel, the flame is stabilized by means of a centrally mounted O₂ pilot strut after being ignited by a plasma torch. During experimental measurements, the fuel is injected with a constant equivalence ratio of 0.8 according to specified strut/wall injection ratios, i.e., a portion of the fuel amount is injected from the strut while the rest is injected from the wall. The strut and wall injectors are arranged at the same axial position. The combustion performance and wall temperature gradients are evaluated with various fuel feeding ratios between the wall and the strut. Experimental results show, when the equivalence ratio is constant and the axial injection position is fixed, the combustion characteristics vary significantly with the strut/wall fuel feeding ratio, especially when this ratio is close to its lowest and highest limits. Among the four fuel feeding ratios examined, the strut only injection mode and the average distributed strut/wall injection mode show the best combustion performance. However, the strut/wall injection mode produces a smaller wall temperature gradient compared to the strut only injection mode, which is due to the significant film cooling effect caused by the wall injected liquid kerosene.     

Traveling ionospheric disturbances observed at South African midlatitudes during the 29–31 October 2003 geomagnetically disturbed period

This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29–31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18°-20° and 27°-28° were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08–2.16 TECU, and 1.07–2.13 h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09 m/s.     

Observational Aspects of Particle Acceleration in Large Solar Flares

Solar flares efficiently accelerate electrons to several tens of MeV and ions to 10 GeV. The acceleration is usually thought to be associated with magnetic reconnection occurring high in the corona, though a shock produced by the Coronal Mass Ejection (CME) associated with a flare can also accelerate particles. Diagnostic information comes from emission at the acceleration site, direct observations of Solar Energetic Particles (SEPs), and emission at radio wavelengths by escaping particles, but mostly from emission from the chromosphere produced when the energetic particles bombard the footpoints magnetically connected to the acceleration region. This paper provides a review of observations that bear upon the acceleration mechanism.     

基于电磁流体动力搅拌器的微流道混合研究

对于许多微流体装置来说,流体的混合是至关重要的。为了实现微流体混合控制,对基于电磁流体动力学原理的微流道主动混合控制方法进行了研究。该方法中使用了一个混合室,在动态洛伦兹力的作用下,混合室内流体往复周期的运动。流体速度的周期性变化使流体分界面折叠,从而使流体接触面增加。用CCD记录设备记录了流体的快速混合过程,并对流体的混合程度进行定量分析。