Visual analysis in a deployable antenna experiment [satellite antenna]

To establish a large deployable antenna, monitoring and collimation are essential for reliable and precise deployment. We have developed an analysis method to detect shifts in several images, in which the combination of cross-correlations between images and approximations at subpixel precision enables us to detect shifts in images with a precision of up to 0.01 pixels. The LDREX mission; which was a preliminary experiment for a large deployable antenna, ETS-VIII, was performed in December 2000. During this experiment, anomalies occurred in the antenna, and deployment was aborted. To understand the cause of the anomalies, we used our visual analysis method. Using this analysis, we detected vibrating features in the antenna, which were useful for explaining the anomalies. We outline our visual analysis method and discuss its application in monitoring the deployable antenna.     

Study of notches in the Earth’s plasmasphere based on data of the <Emphasis Type=\"Italic\">MAGION-5</Emphasis> satellite

Depleted narrow (localized in longitude) regions (field tubes) in the plasmasphere, recently discovered in He⁺ radiation measurements on the IMAGE spacecraft, were first directly observed by the Magion-5 satellite. The low-density regions (notches) occupy <～ 10–30° in longitude and extend from L ～ 2–3 to the plasmasphere boundary in neighboring plasmasphere regions with larger densities. The Magion-5 data give evidence that in the low-density regions temperature is enhanced as compared to the neighboring denser plasmasphere regions. Formation of notches in the plasmasphere is, apparently, associated with AE intensification during weak magnetic storms, while strong magnetic storms usually result in the overall reduction of plasmasphere dimensions. However, even a strong magnetic storm on April 6–7, 2000 (max K _p = 9-and min D _st ～ ?290 nT), but accompanied by an isolated AE impulse, resulted in a density decrease only in the longitudinally limited post-midnight sector of the plasmasphere.     

Terahertz circular dichroism spectroscopy: a potential approach to the in situ detection of life's metabolic and genetic machinery

We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs.     

Global Imaging of Proton and Electron Aurorae in the far Ultraviolet

The IMAGE spacecraft carries three FUV photon imagers, the Wideband Imaging Camera (WIC) and two channels, SI-12 and SI-13, of the Spectrographic Imager. These provide simultaneous global images, which can be interpreted in terms of the precipitating particle types (protons and electrons) and their energies. IMAGE FUV is the first space-borne global imager that can provide instantaneous global images of the proton precipitation. At times a bright auroral spot, rich in proton precipitation, is observed on the dayside, several degrees poleward of the auroral zone. The spot was identified as the footprint of the merging region of the cusp that is located on lobe field lines when IMF B_z was northward. This identification was based on compelling statistical evidence showing that the appearance and location of the spot is consistent with the IMF B_z and B_y directions. The intensity of the spot is well correlated with the solar wind dynamic pressure and it was found that the direct entry of solar wind particles could account for the intensity of the observed spot without the need for any additional acceleration. Another discovery was the observation of dayside sub-auroral proton arcs. These arcs were observed in the midday to afternoon MLT sector. Conjugate satellite observations showed that these arcs were generated by pure proton precipitation. Nightside auroras and their relationship to substorm phases were studied through single case studies and in a superimposed epoch analysis. It was found that generally there is substantial proton precipitation prior to substorms and the proton intensity only doubles at substorm onset while the electron auroral brightness increases on average by a factor of 5 and sometimes by as much as a factor of 10. Substorm onset occurs in the central region of the pre-existing proton precipitation. Assuming that nightside protons are precipitating from a quasi-stable ring current at its outer regions where the field lines are distorted by neutral sheet currents we can associate the onset location with this region of closed but distorted field lines relatively close to the earth. Our results also show that protons are present in the initial poleward substorm expansion however later they are over taken by the electrons. We also find that the intensity of the substorms as quantified by the intensity of the post onset electron precipitation is correlated with the intensity of the proton precipitation prior to the substorms, highlighting the role of the pre-existing near earth plasma in the production of the next substorm.     

Control of a large space structure using MMAE/MMAC techniques

The application of moving-bank multiple model adaptive estimation and control (MMAE/MMAC) algorithms to an actual spade structure (Space Integrated Controls Experiment (SPICE)) being examined at Phillips Laboratory at Kirtland AFB, NM, is presented. The structure consists of a large platform and a smaller platform connected by three legs in a tripod fashion. Kalman filtering and LQG (linear system, quadratic cost, Gaussian noise) control techniques are utilized as the primary design tools for the components of the MMAE/MMAC. Implementing a bank of filters or controllers increases the robustness of the algorithms when uncertainties exist in the system model, whereas the moving bank is utilized to reduce the computational load. Several reduced-order models are developed from the truth model using modal analysis and modal cost analysis. The MMAE/MMAC design with a substantially reduced-order filter model provides an excellent method to estimate a wide range of parameter variations and to quell oscillations in the structure.     

Satellite Angular Motion under the Action of SDOT Magnetic One Axis Sun Acquisition Algorithm

Cosmic Research - Numerical simulation of satellite stabilization towards the Sun for the batteries charge is performed. The magnetic attitude control system implements the Sdot algorithm. It...     

Signatures of Coronal Hole Spectra Between 660 Å and 1460 Å Measured with Sumer on Soho

Spectra of the northern polar coronal hole measured with the SUMER spectrometer on SOHO on 25 October 1996 are analyzed. We present spectra taken at locations on the solar disk where part of the spectrometer slit intersects a polar coronal hole region and an area of brighter emission from outside of the coronal hole area. By comparing the line intensities between the parts of the spectrum taken inside the "dark" area of the coronal holes and the brighter regions, we work out the signatures of the specific coronal hole in the chromosphere, transition region and lower corona. We find that emissions of neutral atom lines, of which there are many in the spectrum of SUMER, show no difference between the coronal hole and the bright boundary areas, whereas all ionized species show strong intensity enhancements, including the continuum emissions of carbon and hydrogen. These enhancements are larger than in normal quiet Sun areas. This revised version was published online in June 2006 with corrections to the Cover Date.     

Complex Indicated Angles Applied to Unresolved Radar Targets and Multipath

The off-axis angle indicated by a conventional monopulse radar is only the real part of a "complex indicated angle." The presence of unresolved targets or multipath distorts the real part (causing an erroneous angle indication) and also produces an imaginary part, which can easily be measured by processing the normally unused quadrature-phase component of the difference signal. Under certain conditions the angles, amplitude ratio, and relative phase of two unresolved targets can theoretically be determined by meas urements of the complex indicated angle on two pulses separated by a short interval. In the special case of multipath, known relationships between the unresolved target and image theoretically permit determination of target elevation with a single pulse.