The Search Coil Magnetometer for THEMIS

THEMIS instruments incorporate a tri-axial Search Coil Magnetometer (SCM) designed to measure the magnetic components of waves associated with substorm breakup and expansion. The three search coil antennas cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. They extend, with appropriate Noise Equivalent Magnetic Induction (NEMI) and sufficient overlap, the measurements of the fluxgate magnetometers. The NEMI of the searchcoil antennas and associated pre-amplifiers is smaller than 0.76 pT $/\sqrt{\mathrm{Hz}}$ at 10 Hz. The analog signals produced by the searchcoils and associated preamplifiers are digitized and processed inside the Digital Field Box (DFB) and the Instrument Data Processing Unit (IDPU), together with data from the Electric Field Instrument (EFI). Searchcoil telemetry includes waveform transmission, FFT processed data, and data from a filter bank. The frequency range covered depends on the available telemetry. The searchcoils and their three axis structures have been precisely calibrated in a calibration facility, and the calibration of the transfer function is checked on board, usually once per orbit. The tri-axial searchcoils implemented on the five THEMIS spacecraft are working nominally.     

A 10 kW DC-DC converter using IGBTs with active snubbers

This full bridge DC-DC converter employs zero voltage switching (ZVS) on one leg and zero current switching (ZCS) on the other. This technique produces exceptionally low insulated-gate bipolar transistor (IGBT) switching losses through the use of an active snubber that recycles energy back to the source. Experimental results are presented for a 10-kW, 20-kHz converter     

HIGH TEMPERATURE MOIRE INTERFEROMETRY TECHNOLOGY

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Multi-Spectral Imager on the Near Earth Asteroid Rendezvous Mission

A multispectral imager has been developed for a rendezvous mission with the near-Earth asteroid, 433 Eros. The Multi-Spectral Imager (MSI) on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft uses a five-element refractive optical telescope, has a field of view of 2.93 × 2.25°, a focal length of 167.35 mm, and has a spatial resolution of 16.1 × 9.5 m at a range of 100 km. The spectral sensitivity of the instrument spans visible to near infrared wavelengths, and was designed to provide insight into the nature and fundamental properties of asteroids and comets. Seven narrow band spectral filters were chosen to provide multicolor imaging and to make comparative studies with previous observations of S asteroids and measurements of the characteristic absorption in Fe minerals near 1 µm. An eighth filter with a much wider spectral passband will be used for optical navigation and for imaging faint objects, down to visual magnitude of +10.5. The camera has a fixed 1 Hz frame rate and the signal intensities are digitized to 12 bits. The detector, a Thomson-CSF TH7866A Charge-Coupled Device, permits electronic shuttering which effectively varies the dynamic range over an additional three orders of magnitude. Communication with the NEAR spacecraft occurs via a MIL-STD-1553 bus interface, and a high speed serial interface permits rapid transmission of images to the spacecraft solid state recorder. Onboard image processing consists of a multi-tiered data compression scheme. The instrument was extensively tested and calibrated prior to launch; some inflight calibrations have already been completed. This paper presents a detailed overview of the Multi-Spectral Imager and its objectives, design, construction, testing and calibration.     

Near Magnetic Field Investigation,Instrumentation, Spacecraft Magnetics and Data Access

The primary objective of the investigation is the search for a body-wide magnetic field of the near Earth asteroid Eros. The Near Earth Asteroid Rendezvous (NEAR) 3-axis fluxgate magnetometer includes a sensor mounted on the high-gain antenna feed structure. The NEAR Magnetic Facility Instrument (MFI) is a joint hardware effort between GSFC and APL. The design and magnetics approach achieved by the NEAR MFI effort entailed low-cost, up-front attention to engineering solutions which did not impact the schedule. The goal of the magnetometer is reliable magnetic field measurements within 5 nT, which necessitates the use of an extensive spacecraft magnetic interference model but is achievable with the full year's orbital data set. Such a goal has been shown viable with recent in-flight calibration data and comparisons to the WIND magnetometer data. The NEAR MFI effort has succeeded in providing magnetic field measurements for the first flight in NASA's Discovery line.     

CIR Morphology, Turbulence, Discontinuities, and Energetic Particles

Corotating interaction regions (CIRs) in the middle heliosphere have distinct morphological features and associated patterns of turbulence and energetic particles. This report summarizes current understanding of those features and patterns, discusses how they can vary from case to case and with distance from the Sun and possible causes of those variations, presents an analytical model of the morphological features found in earlier qualitative models and numerical simulations, and identifies aspects of the features and patterns that have yet to be resolved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energetic Ions Observed at Low to High Latitudes in the Southern Heliosphere During Declining and Rising Solar Activity

We present and compare observations of energetic protons during the two first transits of the Ulysses spacecraft from low to high latitudes in the southern heliosphere. Protons in the energy range 1.8–3.8 MeV from the COSPIN experiment are studied for global trends and in relation to some ambient structures in the solar wind (corotating interaction region, forward/reverse shock). The global trends show the large dependence on the heliospheric condition and solar activity, including indications of a larger ambient particle population during the rising phase of solar activity and more efficient solar wind particle accelerators during the declining phase. More enhancements in the proton flux intensity are time associated with forward shocks than reverse contrary to first pass. Recurrent structures are found even during the second transit. Some latitude dependent periodicities are observed that could relate to the differential solar rotation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temporal and Spatial Variation of the Ion Composition in the Ring Current

A global view of the ring current ions is presented using data acquired by the instrument MICS onboard the CRRES satellite during solar maximum. The variations of differential intensities, energy spectra, radial profile of the energetic particles and the origin of the magnetic local time (MLT) asymmetry of the ring current have been investigated in detail. O⁺ ions are an important contributor to the storm time ring current. Its abundance in terms of number density increases with increasing geomagnetic activity as well as its energy density. However, a saturation value for the energy density of O⁺ ions has been found. The low-energy H⁺ ions show a dramatic intensification and a rapid decay. However, its density ratio during the storm maximum is almost constant. On the other hand, high-energy H⁺ ions first exhibit a flux decrease followed by a delayed increase. Its density ratio shows an anti-correlation with the storm intensity. Both the positions of the maximum flux of O⁺ and He⁺ depend on storm activity: they move to lower altitudes in the early stage of a storm and move back to higher L-values during the recovery phase. Whereas the position of H⁺ and He⁺⁺ show almost no dependence on the Dst index. The energy density distributions in radial distance and magnetic local time show drastic differences for different ion species. It demonstrates that the ring current asymmetry mainly comes from oxygen and helium ions, but not from protons. The outward motion of O⁺ around local noon may have some implications for oxygen bursts in the magnetosheath during IMF Bz negative conditions as observed by GEOTAIL.