Single-event upsets in the Cluster and Double Star Digital Wave Processor instruments

Radiation-induced upsets are an important issue for electronic circuits operating in space. Upsets due to solar protons, trapped protons, and galactic cosmic rays are frequently observed. Modeling the expected frequency of upsets is a necessary part of the design process for space hardware. The Cluster and Double Star spacecraft were respectively European and Chinese missions dedicated to the study of the wave and particle environment in the Earth's magnetosphere. All four Cluster spacecraft and one Double Star spacecraft included a Digital Wave Processor (DWP) instrument. The primary purpose of this instrument was as the central controller of the Wave Experiment Consortium. This paper investigates the occurrence of radiation-induced single-event upsets in these DWP instruments. The memory devices used in the DWP were not specifically radiation-hardened parts and so are relatively sensitive to single-event effects. We present the experience gained during the first 11 years of operation of the Cluster mission and the nearly 4 year lifetime of the Double Star TC-1 spacecraft and compare with models of the radiation environment

Accidental and methodical defects of generation of precision and ultraprecision surfaces of polymer optics

Widespread adoption of precision and ultraprecision articles from the polymeric materials creates a need for the understanding of a mechanism of the new high quality surfaces generation by the controlled fracture processes in the single-point diamond machining. The efficacious way for this understanding is a creation of the model of the surface layer forming process as result of the formation of its accidental and methodical defects by the precision microcutting

RUNNING SHOE STIFFNESS:THE EFFECT ON WALKING GAIT

Sports shoes can be grouped into various categories based on their stability, protection capabilities, traction, impact characteristics and stiffness. The majority of shoe tests involve measures of traction and impact. Few studies have examined shoe sole stiffness. Therefore, the purpose of this study was to assess shoe sole stiffness by a materials testing procedure, and then examine the effect of shoe stiffness on walking gait. A damped oscillation technique, previously used on muscle-tendon complexes, was utilised to calculate the stiffness and the damping factor of six types of running shoes. The shoes used different rnidsole components which included air sacs, gel sacs, ethylene vinyl acetate (EVA), and kevlar reinforcing. Two shoes at the extremes of the range were then selected from the materials test results for use in the subsequent gait analysis. Nine males ranging in age from 25 to 45 years (mean =36 years) participated in the experiment. Heights ranged from 186cm to 176cm (mean=182cm) and weights ranged from 72.5kg to 89kg (mean=8lkg). No subjects had any musculoskeletal problems affecting the lower limb. Two dimensional video data were collected on the right leg using an Ariel Video Analysis system sampling at 50 Hz, as subjects walked at 5.1 km/hr on a motor driven treadmill. Markers were placed on the greater trochanter, lateral condyle of the femur, lateral malleolus of the fibular, the heel of the shoe and on the shoe at the level of the fifth metatarsal head. Three stride cycles were collected after the subjects had walked on the treadmill for one minute. Data were digitised and downloaded to FMAP software to calculate kinematic variables such as knee and ankle angle and knee and ankle angular velocity. Data were then normalised to 50 points and averaged across stride cycles and subjects. Although a comparison of the stiff and flexible shoes indicated no differences in the kinematic parameters (p>0.05), it may be that the muscles of the lower limb adjust their activity level for the stiffness of the shoe to maintain an invariant kinematic pattern

Modelling and Prediction of Global Magnetic Disturbance in Near-Earth Space: a Case Study for Kp Index using NARX Models

Severe geomagnetic disturbances can be hazardous for mod-ern technological systems. The reliable forecast of parameters related to thestate of the magnetosphere can facilitate the mitigation of adverse effects ofspace weather. This study is devoted to the modeling and forecasting of theevolution of the Kp index related to global geomagnetic disturbances. Through-out this work the Nonlinear AutoRegressive with eXogenous inputs (NARX)methodology is applied. Two approaches are presented: i) a recursive slid-ing window approach, and ii) a direct approach. These two approaches arestudied separately and are then compared to evaluate their performances.It is shown that the direct approach outperforms the recursive approach, butboth tend to produce predictions slightly biased from the true values for lowand high disturbances

Investigation of the Chirikov resonance overlap criteria for equatorial magnetosonic waves

Observations of equatorial magnetosonic waves made during the Cluster I nnerMagnetospheric Campaign clearly show discrete spectra consisting of emissions around harmonics of theproton gyrofrequency. Equatorial magnetosonic waves are important because of their ability to efficientlyscatter electrons in energy and pitch angle. This wave-particle interaction is numerically modeled throughthe use of diffusion coefficients, calculated based on a continuous spectrum such as that observed byspectrum analyzers. Using the Chirikov overlap resonance criterion, the calculation of the diffusioncoefficient will be assessed to determine whether they should be calculated based on the discrete spectralfeatures as opposed to a continuous spectrum. For the period studied, it is determined that the discretenature of the waves does fulfill the Chirikov overlap criterion and so the use of quasi-linear theory with theassumption of a continuous frequency spectrum is valid for the calculation of diffusion coefficients

Prediction of Kp Index Using NARMAX Models with A Robust Model Structure Selection Method

The severity of global magnetic disturbances in Near-Earth space can crucially affect human life. These geomagnetic disturbances are often indicated by a Kp index, which is derived from magnetic field data from ground stations, and is known to be correlated with solar wind observations. Forecasting of Kp index is important for understanding the dynamic relationship between the magnetosphere and solar wind. This study presents 3 hours ahead prediction for Kp index using the NARMAX model identified by a novel robust model structure detection method. The identified models are evaluated using 4 years of Kp data. Overall, the models with robust structure can produce very good Kp forecast results and provide transparent and compact representations of the relationship between Kp index and solar wind variables. The robustness and conciseness of the models can highly benefit the space weather forecast tasks

Cluster observations of non-time-continuous magnetosonic waves

Equatorial magnetosonic waves are normally observed as temporally continuous sets of emissions lasting from minutes to hours. Recent observations, however, have shown that this is not always the case. Using Cluster data, this study identifies two distinct forms of these non-temporallycontinuous emissions. The first, referred to as rising tone emissions, are characterised by the systematic onset of wave activity at increasing proton gyroharmonic frequencies. Sets of harmonic emissions (emission elements) are observed to occur periodically in the region ±10◦ off the geomagnetic equator. The sweep rate of these emissions maximises at the geomagnetic equator. In addition, the ellipticity and propagation direction also change systematically as Cluster crosses the geomagnetic equator. It is shown that the observed frequency sweep rate is unlikely to result from the sideband instability related to nonlinear trapping of suprathermal protons in the wave field. The second form of emissions is characterised by the simultaneous onset of activity across a range of harmonic frequencies. These waves are observed at irregular intervals. Their occurrence correlates with changes in the spacecraft potential, a measurement that is used as a proxy for electron densit

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Experimental determination of the dispersion relation of magnetosonic waves

Magnetosonic waves are commonly observed in the vicinity of the terrestrial magnetic equator. It has been proposed that within this region they may interact with radiation belt electrons, accelerating some to high energies. These wave-particle interactions depend upon the characteristic properties of the wave mode. Hence, determination of the wave properties is a fundamental part of understanding these interaction processes. Using data collected during the Cluster Inner Magnetosphere Campaign, this paper identifies an occurrence of magnetosonic waves, discusses their generation and propagation properties from a theoretical perspective, and utilizes multispacecraft measurements to experimentally determine their dispersion relation. Their experimental dispersion is found to be in accordance with that based on cold plasma theory

Enhanced timing accuracy for Cluster data

The standard timing accuracy for the Cluster mission is ±2 ms. However for inter-spacecraft comparisons of waveform data, a much higher accuracy is needed – for example a timing error of 1 ms results in a phase error of 65° for a signal at 180 Hz. Most Cluster data are recorded on an onboard solid state recorder and time-stamped using an onboard clock which is calibrated to coordinated universal time (UTC). Until recently, the error of this onboard clock was allowed to increase to the ±2 ms limit before a new calibration was applied. However, the timing error for real-time data is estimated to be only ~11 μs, so these data may be used to prepare a time correction data set which allows the standard timing accuracy to be improved considerably. This paper describes the details of the preparation and validation of this data set. Two independent source data sets are used: telemetry to European Space Agency (ESA) ground stations supporting the main operations of the Cluster spacecraft, and the real-time telemetry to the NASA Deep Space Network (DSN) stations supporting the Wide-Band Plasma Wave Investigation