Enhanced resolution in simple radars

Many simple radars use fact-risetime pulses, but wide bandwidth does not translate into corresponding high resolution since the spectrum is far from flat. A scheme for enhancing down- and cross-range resolution of multiple targets through a two-step partial equalization of the spectrum is illustrated by detailed computer simulation, with emphasis on the tradeoffs between resolution and signal-to-noise ratios. Three examples are treated: two equal scattering centers, two unequal scattering centers, and compound target     

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     

Incremental planning to control time-constrained blackboard-basedproblem solver [vehicle monitoring]

A planner that improves the control decisions made by a blackboard-based problem solver is described. This planner interleaves planning and execution. It sketches out major plan steps but incrementally details actions for only the next step since earlier actions influence how (and whether) to pursue a plan. The planner also reasons about time constraints, revising plans to meet problem-solving deadlines and deciding when it has done enough work on a problem. Implementation of these mechanisms is outlined, and experiments are discussed showing how they reduce overall computation and improve problem solving     

Physical interpretation of interdisciplinary solar/interplanetary observations relevant to the 27–29 June 1980 SMY/STIP event no. 5

A sequence of six well defined interplanetary structures (magnetic clouds) was identified in the solar wind and magnetic field measurements of Helios-1 from 29 June-01 July, 1980. (location 0.64–0.67 AU, C. Long. ～165°, C. Lat. ～5.8°). These structures were characterized by a large northward directed solar wind flow; by well defined directional discontinuities of mainly the ‘tangential-type’ at their beginnings and ends; by some increase in proton and by very pronounced increases in alpha particle number densities - each accompanied by sudden temperature decreases (or in one case by an increase); by some times an increase in magnetic field strength and by values of Nα/Np typical of the inner solar atmosphere. These structures are suggested to have been ejections from a succession (27–29 June, 1980) of Type II producing flares in Hale Region 16923 which coronagraph and X-ray (GOES) data indicate constituted a family of transient producing events. Only two interplanetary shocks were identified in the relevant Helios-1 records. It is suggested on the basis of observations of the directionality of certain of the flare related Type II bursts that some of these shocks could have been missed by the spacecraft. This implies that, in the absence of directional information, correlation of an observed interplanetary shock wave with a solar Type II burst may not always lead to a unique result.     

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.     

Ambiguity Resolution for Satellite Doppler Positioning Systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yieds conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form compasison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.     

Signatures of troposphere-stratosphere momentum coupling: Implications for global atmospheric angular momentum and earth rotation budgets

During January–August 1978, the global atmospheric angular momentum (M) exhibits distinct patterns of short term momentum interchange across latitudes. In the northern hemisphere winter-spring season, 30–50 day modulations of M are present in which momentum $\text{enhancements}$ at mid-latitudes (20–30°) are closely matched by momentum $\text{depressions}$ at high latitudes (50–60°). During the same interval there are no corresponding variations in M evident in the southern hemisphere. Conversely, during southern hemisphere fall-winter, similar anticorrelations in monthly scale momentum excursions are evident between mid and high latitudes. In the northern hemisphere, the winter-spring momentum signatures are detected throughout the atmosphere, from the lower troposphere to the stratosphere. During the southern hemisphere fall-winter, the modulation patterns are not evident at the higher altitudes. Structural details of the momentum signatures indicate that the coupling is sometimes effective on very short time scales, e.g. 1–2 days, or less. The evidence of distinct anti-correlation between large regions has interesting implications for studies of global atmospheric circulation, and also for studies of the excitation of variations in earth rotation in response to short term modulations of M.