A Three-Dimensional Simulation of Collisional-Interchange-Instability in the Equatorial-Low-Latitude Ionosphere

We present a three-dimensional simulation of collisional-interchange-instability in the equatorial-low-latitude F region of ionosphere. The instability is responsible for the generation of large plasma density depletion or bubble. General 3D potential and continuity equations are derived to simulate the phenomena. To understand the linear aspect of the instability, the general 3D linear growth rate is derived using 3D potential equation. The linear growth characteristics are compared with earlier field-aligned-integrated growth analyses. The numerical simulation of bubble in the 3D spherical polar geometry is finally presented. Distinct evolution characteristics of bubble in 3D and 2D simulation are further discussed.     

Detection of suprathermal ionospheric O+ ions inside the plasmasphere

The plasma diagnostic experiments on the AUREOL-3 satellite have revealed flows of low energy 0⁺ ions deep inside the night plasmasphere during a large substorm. Flux gradients of the 0⁺ ions were accompanied by enhancements of ELF electric field noise. The appearance of suprathermal ions at $\text{L ? 2.5 – 3}$ is interpreted within the framework of electrostatic ion-cyclotron acceleration of ionospheric ions in the diffuse auroral zone /12/ followed by a radial displacement of these ions inside the plasmasphere driven by azimuthal electric fields during substorm activity. Electrostatic oscillations observed inside the plasmasphere are apparently associated with gradient instability at the sharp boundaries of suprathermal ion flows.     

Investigation of Hypervelocity Impacts on Retrieved Surfaces by Direct Simulation Monte Carlo

Hypervelocity impacts on the retrieved Hubble Space Telescope (HST) solar array was investigated by our extended Direct Simulation Monte Carlo (DSMC) model and the result matches well with the measured data in most of the particle mass range. The revelation of the altitude dependence of particles flux onto the retrieved surfaces provides some insight in understanding the observed higher flux onto Mir space station relative to that onto Long Duration Exposure Facility (LDEF). Our analysis suggests that a slightly higher primary flux onto Mir space station would be possible even without taking into account the secondary impacts, as a result of the existence of the highly eccentric orbits of small-sized debris. It is, furthermore, predicted that 43% of the measured impact flux onto Mir station in PIE experiment may be from secondary impacts, and a corresponding 7% for the detectors in Echantillions experiment.     

Classification of solar wind structures and intense geomagnetic storm alarms with self-organizing maps

Intense geomagnetic storms (D_st < −100 nT) usually occur when a large interplanetary duskward-electric field (with Ey > 5 mV m⁻¹) lasts for more than 3 h. In this article, a self-organizing map (SOM) neural network is used to recognize different patterns in the temporal variation of hourly averaged Ey data and to predict intense storms. The input parameters of SOM are the hourly averaged Ey data over 3 h. The output layer of the SOM has a total of 400 neurons. The hourly Ey data are calculated from solar wind data, which are provided by NSSDC OMNIWeb and ACE spacecraft and contain information on 143 intense storms and a fair number of moderate storms, weak storms and quiet periods between September 3, 1966 and June 30, 2002. Our results show that SOM is able to classify solar wind structures and therefore to give timely intense storm alarms. In our SOM, 21 neurons out of 400 are identified to be closely associated with the intense storms and they successfully predict 134 intense storms out of the 143 ones selected. In particular, there are 14 neurons for which, if one or more of them are present, the occurrence probability of intense storms is about 90%. In addition, several of these 14 neurons can predict big magnetic storm (D_st  −180 nT). In summary, our method achieves high accuracy in predicting intense geomagnetic storms and could be applied in space environment prediction.     

Effect of KOH concentration on LEO cycle life of IPVnickel-hydrogen flight cell-update II

For update I see Energy and Environment: A Continuing Partnership, vol.3, American Nuclear Society (1991). An update of validation test results confirming the breakthrough in the low-Earth-orbit (LEO) cycle life of nickel-hydrogen cells containing 26% KOH electrolyte is presented. The results are part of an investigation of the effect of KOH concentration on life cycle. The cycle life of boiler plate cells was about 40000 LEO cycles compared to 3500 cycles for cells containing 31% KOH. The cycle regime was a stressful accelerated LEO, which consisted of a 27.5 min charge followed by a 17.5 min discharge (2×normal rate). The depth-of-discharge (DOD) was 80%. The cell temperature was maintained at 23°C. Results for six 48-Ah recirculation design IPV nickel-hydrogen flight battery cells currently being evaluated to validate the above findings are reported. Three of the cells contain 26% KOH (test cells), and three contain 31% KOH (control cells). They are undergoing real-time LEO cycle life testing. The 31% KOH cells failed at cycles 3729, 4165, and 11355. One of the 26% KOH cells failed at cycle 15314. The other two 26% KOH cells have been cycled for over 16600 cycles without failure     

Travelling heater growth of GaSb under reduced gravity during the first spacelab-mission

Single crystals of binary III-V-semiconductors, e.g. GaAs or InP, are important basic materials for optoelectronic devices, e.g. LED's and lasers. Device production needs highly perfect substrate crystals with low defect densities and homogeneous dopant distributions. In our experiment we applied the Travelling-Heater-Method to grow the III-V compound GaSb. The aim of this research project was to improve the crystal quality by investigating convective transport phenomena and the origins of dopant inhomogeneities under earth and space conditions. Earth grown crystals show strong dopant variations mainly due to convective flow phenomena. The preliminary result of our SPACELAB 1 experiment reveals an increase of dopant homogeneity in the space grown crystal because of the absence of natural convection under reduced gravity.     

Mesospheric ozone densities deduced from solar occultation measurements

Quartz-UV occultation measurements by the satellite Interkosmos-16 have been used to calculate ozone densities at altitudes between 50 and 90 km for the period August to October 1976. Below 65 km densities agree well with the Krueger-Minzner-model. Mesopause densities have been studied in some detail. A certain percentage of the profiles show close correlation with the model of Shimazaki and Laird (with a pronounced minimum below the mesopause) while others fit better to the Park and London model (no minimum). This variability of the ozone density may be caused by different processes in the photo-chemistry of ozone. Two possible causes, the temperature dependent rate coefficients and the odd hydrogen processes are discussed in greater detail.     

GPS modeling for designing aerospace vehicle navigation systems

The complexity of the design of a Global Positioning System (GPS) user segment, as well as the performance demanded of the components, depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system can also affect the user segment design. Models of GPS measurements are used to predict user segment performance at various levels. Design curves are developed which illustrate the relationship between user requirements, the user segment design, and component performance