Hydra — A 3-dimensional electron and ion hot plasma instrument for the POLAR spacecraft of the GGS mission

HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program. A consortium of institutions has designed a suite of particle analyzers that sample the velocity space of electron and ions between 2 keV/q – 35 keV/q in three dimensions, with a routine time resolution of 0.5 s. Routine coverage of velocity space will be accomplished with an angular homogeneity assumption of 16°, appropriate for subsonic plasmas, but with special 1.5° resolution for electrons with energies between 100 eV and 10 keV along and opposed to the local magnetic field. This instrument produces 4.9 kilobits s^–1 to the telemetry, consumes on average 14 W and requires 18.7 kg for deployment including its internal shielding. The scientific objectives for the polar magnetosphere fall into four broad categories: (1) those to define the ambient kinetic regimes of ions and electrons; (2) those to elucidate the magnetohydrodynamic responses in these regimes; (3) those to assess the particle populations with high time resolution; and (4) those to determine the global topology of the magnetic field. In thefirst group are issues of identifying the origins of particles at high magnetic latitudes, their energization, the altitude dependence of the forces, including parallel electric fields they have traversed. In thesecond group are the physics of the fluid flows, regimes of current, and plasma depletion zones during quiescent and disturbed magnetic conditions. In thethird group is the exploration of the processes that accompany the rapid time variations known to occur in the auroral zone, cusp and entry layers as they affect the flow of mass, momentum and energy in the auroral region. In thefourth class of objectives are studies in conjunction with the SWE measurements of the Strahl in the solar wind that exploit the small gyroradius of thermal electrons to detect those magnetic field lines that penetrate the auroral region that are directly open to interplanetary space where, for example, the Polar Rain is observed.     

Measurement of Distributed Targets with the Random Signal Radar

A model of a distributed target as a collection of independent, Poisson distributed point scatterers or scattering centers in a range-velocity target space is introduced and is characterized by a deterministic function called the ?scatterer density function.? This function is the density of the point scatterers in the range-velocity space and can be estimated in a relatively straightforward manner by any radar having adequate resolution in both range and velocity and no ambiguities in the region occupied by the distributed target. The use of the random signal radar with a correlator receiver is considered here and the statistical properties of the correlator output, when the return signal is from a distributed target, are derived. It is shown that the spectral density is simply related to the scatterer density function. The technique is illustrated by an example in which the target is a tornado modeled as a cylinder with constant angular velocity. The example suggests that is a possible to remotely estimate the radar cross section per unit volume as a function of distance from the center of the tornado.     

Nondestructive Characterization of RBSOA of High-Power Bipolar Transistors

Reverse-bias safe operating area (RBSOA) of high-power Darlington transistors is characterized using a 120 A/1000 V nondestructive reverse-bias second breakdown tester designed and fabricated at Virginia Polytechnic Institute and State University. Elaborate RBSOA characteristics are generated with different forward/reverse base drives and collector current levels. The effects of elevated case temperature and second-base drive on RBSOA of four-terminal Darlington devices are also discussed.     

Comparison of half-bridge off-line, ZCS-QRC and ZVS-MRC

The performance of the half-bridge (HB) zero-current-switched (ZCS) quasi-resonant converter (QRC) and zero-voltage-switched (ZVS) multiresonant converter (MRC) is compared with respect to their efficiency, input voltage range, semiconductor stresses, power density, and reliability. The efficiency of the HB ZVS-MRC at a given nominal input is shown to be highly dependent on the range of the input voltage, and it suffers when the converter has to be designed to cover a wide range. However, this is not the case for the HB ZCS-QRC. Experimental versions of the HB ZCS-QRC and HB ZVS-MRC were designed for the input voltage range from 150 to 350 V and a maximum output power of 100 W, under the same constraints, to facilitate their comparison     

The relation of Algols and W Serpentis stars

Evidence on the issues of whether the W Serpentis stars are a coherent class, and how they may interface with the Algol systems, is reviewed, with emphasis on the idea that they are semi-detached systems in the latter part of the rapid phase of mass transfer, with optically and geometrically thick disks of transferred gas around the (now) more massive star. We are interested in what will be seen when the gas clears away, and mainly examine the idea that it will be an Algol-type system. More particularly, consideration is given to centrifugally limited accretion as a mechanism to build up a substantial disk, and the presumed evolutionary sequence is from a W Ser to a rapidly rotating Algol to a normal Algol system. Systems such as V367 Cyg and RW Tau fit into this scheme only with difficulty. Because it is extremely difficult to measure the rotation of some W Ser (mass) primaries, it is natural to look at the rotation statistics of Algols to test this idea. The badly behaved light curves and spectroscopy of some Algols (eg. U Cep, RZ Sct) may be attributable to the double contact condition, and the ramifications of this possibility are discussed. If so, the rotation statistics of Algols should show two spikes, corresponding to the two special conditions into which a system should be driven by tidal braking and centrifugally limited spinup. Present rotation statistics do show these spikes. Algols should flip between these states fairly quickly, depending on the mass transfer rate. Thus, to the extent that the meager statistics can be accepted as meaningful, the new (fourth) morphological type of close binary (double contact) has attained demonstrable reality. The rotation statistics are presented in terms of a particular rotation parameter, R, which is zero for synchronism and unity for the centrifugal limit. Future work should develop rotation statistics to see if the rotational lobe-filling (R = 1) spike persists. It should also look into whether W Ser primaries are on the hydrogen burning main sequence, or in general what they are. We also need more light curves of W Ser type systems, high resolution line profiles for the (mass) primaries (with particular attention to the W Ser-Algol transition cases), and spectroscopy of low inclination W Serpentis systems, such as KX And.     

Filtering of discontinuous processes arising in marine integratednavigation systems

A refined stochastic model for the errors of the Loran-C radio navigation aid is described, and it is shown how this model can be used to improve the performance of integrated navigation systems. In addition to the usual propagation errors, Loran-C time of arrival measurements are occasionally plagued with sudden intermittent errors of a particular magnitude and caused by receiver cycle selection errors. These result in sudden large jumps in the calculated position solution. The Loran-C error has been modeled as the sum of a diffusion process, representing the normal propagating errors, and a pure jump process of Poisson type, representing the cycle selection errors. A simple integrated navigation system is then described, based on the Loran-C model and the standard dead reckoning (heading and speed) system model. Assuming that the observed process is governed by a linear stochastic difference equation, a recursive linear unbiased minimum variance filter is developed, from which the Loran-C and dead reckoning errors, and hence position and velocity, can be estimated     

A methodology for addressing support equipment obsolescence

The rapid growth of technology over the last twenty years is providing vastly improved capabilities for both avionics and avionics test systems. Unfortunately, an environment of rapid technological growth breeds a corresponding environment of rapid technological obsolescence. Test systems developed fifteen years ago are becoming increasingly more difficult to support due to obsolescence issues and, additionally, such a test system does not reflect the current state-of-the-art for automatic test equipment. The ability of a test system to evolve is essential to providing cost-effective support systems for electronic systems. The F-15 Tactical Electronic Warfare System (TEWS) Intermediate Support System (TISS) was developed under the Modular Automatic Test Equipment (MATE) guidelines to support the suite of F-15 electronic warfare LRUs. MATE imposed hardware architecture constraints, which were factors that contributed to its abandonment. However, the modular aspect of MATE has provided a system that can easily evolve with technological advancements. Modularity is the cornerstone of modern software systems and this is the aspect that has been exploited in the evolution of the TISS