Cross Correlation of Orthogonally Polarized Backscatter Components

The backscattering of an elliptically polarized plane wave from two kinds of complex radar objects is considered from the standpoint of coherency theory, and the antenna polarizations that give rise to maximum correlated and uncorrelated orthogonally polarized components in the receiving channels are discussed. The resulting observations may find application in radar systems which use the correlation between the received orthogonally polarized components for detecting targets in natural and man-made interference.     

Synthesis and test issues for future aircraft inertial systemsintegration

A survey is presented of the potential benefits, possible pitfalls, and anticipated testing needs of integrating inertial guidance systems with systems dependent on the availability of the electromagnetic spectrum. Commonly referred to as integrated communications, navigation, and identification avionics (ICNIA), these systems of the future offer the combined potential for superb positioning and secure communications. The general characteristics (if current development trends continue) of the next-generation inertial navigation systems (INS) are briefly presented, followed by key modular and conceptual issues in the synthesis of this INS with systems dependent on the EM spectrum. Modular issues as considered here are those related to detailed implementation and resulting efficiency. Conceptual issues are those related to overall military strategy and resulting effectiveness. An example of modular systems integration is given, and a few preparations which can be anticipated for the field testing of integrated systems are presented, followed by concluding comments     

Problems in the analysis of gamma-ray burst spectra

Spectral measurements by the Solar Maximum Mission have been used to confirm the cyclotron lines in gamma-ray bursts reported from the Konus experiment. We present ISEE-3 data for the same burst (GB800419) during the same period of time which show no line. We discuss various problems in the analysis of scintillator spectra and point out that unfolded spectra are not necessarily unique and that the position of a data point in a deconvolved spectrum may vary depending on the assumed overall shape of the spectrum. As a result, if the analysis assumes a soft spectrum (such as optically thin thermal bremsstrahlung) an absorption feature might appear, whereas a harder spectrum (such as a Comptonized blackbody) would not require the feature. Since the continuum shape probably changes during the duration of a typical burst, the nonuniqueness of the spectral unfolding, combined with the assumption that the continuum is optically thin thermal bremsstrahlung, could give rise to spurious “absorption” features which vary on a time scale of seconds. Despite these problems, there is still some evidence for $\text{narrow}$ spectral lines in the range 45 to 65 keV but not for the broad lines reported from the Konus experiment. Unfortunately, the range 45 to 65 keV is the most difficult spectral region to unfold.     

Real-time stereoscopic applications using the goes operational satellites

We have investigated the use of real and synthetic stereo satellite images and stereo graphics in applications such as cloud-tracked winds, severe storm cloud analysis, and general meteorological interpretation. We have concluded that a stereo meteorological presentation is possible and desirable in an operational environment. Synthetic stereo could be used immediately in cloud-tracked wind operations. The presentation allows one to appreciate the interrelations between cloud motions and cloud structures, especially in multi-layered situations. Reprocessing of FGGE tropical wind sets with a synthetic stereo presentation showed some improved yields of low-level vectors, a significant increase in mid-level vectors, and very little change in the high-level vectors. Severe local storm real-stereo presentations are possible operationally because the 15 minute RISOP operations of GOES-East allow simultaneous scanning of both geosynchronous satellites twice per hour. The real-stereo height measurements of overshooting turrets are an improvement over infrared heights and can be used to monitor the strength of the thunderstorm updraft. Synthetic stereo presentations of thunderstorm tops can be presented in a non-linear fashion which stretches out the cloud top features. The synthetic stereo presentation is easier for most people to see. We recommend the use of a hybrid system where the viewing is done on the synthetic stereo image and the quantitative measurements are done on the real-stereo pairs.     

Lightweight (AlGaAs)GaAs/CuInSe2 tandem junction solarcells for space applications

Mechanically stacked tandem cells consisting of GaAs thin-film upper cells and CuInSe₂ thin-film lower cells have been developed to meet the increasing power needs projected for future spacecraft. The authors report the fabrication of the first highly efficient lightweight GaAs/CuInSe₂ tandem cell on a 2-mil thick substrate, update recent performance improvements in thin-film GaAs/CuInSe₂ tandem cells, and discuss their application to space power systems. The efficiency of 4-cm² cells has improved to 21.6% AM0, the highest ever reported for a thin-film photovoltaic cell. Lightweight 4-cm² tandem cells have been successfully fabricated with efficiencies as high as 20.8%. These cells weighed about 180 mg without optimized substrate trimming. Radiation and operating temperature effects on GaAs/CuInSe₂ tandem cells are also discussed, and an interconnect scheme to form a voltage-matched string is described     

LIPS III-a solar cell test bed in space

The LIPS III satellite, which was launched into a 1100-km circular orbit of 60° inclination in the spring of 1987, is discussed. LIPS III is a member of the living-plume-shield class of spacecraft, all of which were built around a simple sheet metal plume deflector. The purpose of LIPS III was to provide a testbed for space power sources. An overview of the LIPS III system is given, and the experiments submitted for it, all but one of which were photovoltaic in nature, are described     

Highly variable X-ray emitting objects in the Rho Oph dark cloud

The Rho Ophiuchi dark cloud region has been the subject of an extensive guest investigation using the $\text{Einstein}$ Observatory. The set of observations comprise 14 IPC fields and 3 HRI fields. The densest part of the cloud has been observed 6 times. Forty seven sources were detected at a level > 3.5 σ and twenty more above 2 σ. The majority of these sources have optical, IR, or even radio continuum counterparts; nine are identified with known T Tauri stars, while several others are identified with stars showing H α in emission. All show a high degree of time variability; flux variations reach factors of 5 in a few hours, or 25 in a day. Apparent luminosities are in the range 10(30) – 10(31)(1) erg.s^?1. The possibility that the X-ray variability is due to flares is examined. If this interpretation is correct, one source has been the seat of the largest stellar flare ever recorded in X rays [L_x = 10(32) erg.s^?1, E_x ?10(36) ergs^-].     

Radar auroral observations and ionospheric electric fields

The ground-based systems STARE and SABRE utilize radar auroral phenomena to estimate ionospheric electric fields. Some of the assumptions underlying these systems have been tested and general agreement with expectations have been found. However, as the results have been analysed in detail, it has become clear that the error in the irregularity drift velocity can at times amount to 100 ms^?1. Direct comparisons with other E-field measurements, as well as assessments of the results of applications of the Stare data clearly demonstrate that the electric field, calculated on the basis of the irregularity drift velocity, is a useful estimate of the actual horizontal electric field in the ionosphere and is sufficiently accurate for a great variety of geophysical studies.     

X-ray burst sources — A simple two zone model

With the help of a very simple two zone model, we demonstrate the possibility of periodic thermal relaxation (limit cycle) oscillations in the helium burning envelope of accreting neutron stars. Physically reasonable model parameters can be chosen which yield agreement with the observed features of x-ray bursts and we suggest that this limit cycle is operative in neutron stars which have an accretion rate in a specific range. For hydrogen burning a similar cycle is possible, but it operates at such high temperatures that an unrealistically large accretion rate would be required.