Interference Immunity Effects in CPSK Systems with Hard-Limiting Transponders

Transmission characteristics are described for M-ary coherent phase-shift keyed (CPSK) systems with N-stage hard-limiting transponders where noise and multiple continuous wave (CW) interference sources are additively combined in each link. A general expression for the probability density function of the composite phase at the final link is derived; the overall error probability is then obtained from this general expression. Comparisons with N-cascaded linear amplifier systems clearly show the noise and interference immunity that result from the use of bandpass hard limiters (BPHLs). The BPHL system's error probability improvement versus interference sources is shown to be much larger than the improvement versus noise.     

Microprocessor-Controlled Digital Shunt Regulator

A new approach to the design of power systems is presented in which a microprocessor is used as a controller for a digital shunt regulator (DSR). This approach meets the demands of future space and ground missions, i. e., high efficiency, high reliability, low weight, low volume, increased flexibility, and less development time. This approach responds to future demands by permitting realtime modification of system parameters for system optimization. This feature is especially important in the event of an anomaly. As the microprocessor need not be dedicated to the DSR, it can simultaneously be used for battery management and for charge regulator/discharge regulator control. This approach also reduces the component count, simplifies assembly and testing of the unit, results in significant time saving, and increases the reliability.     

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.     

The sensitivity of the earth's radiation budget to changes in cloudiness

Cloudiness modulates the radiation budget at the top of the Earth-atmosphere system. For radiation balance studies, for climate diagnostic studies, and for climate modeling studies, it is important to know the sensitivity of both the outgoing longwave radiation and the net (absorbed solar minus outgoing longwave) radiation of the system to changes in cloudiness on a global basis. Based on a 45 month series of NOAA satellite scanning radiometer observations, estimates of the global distribution of these sensitivity parameters are obtained.     

Energetics of the magnetosphere

Energy flow in various large-scale processes of the Earth's magnetosphere is examined. This energy comes from the solar wind, via the dawn-to-dusk convection electric field, a field established primarily by magnetic merging but with viscous-like boundary interaction as a possible contributor. The convection field passes about 5 × 10¹¹ W to the near-Earth part of the plasma sheet, and also moves the plasma earthward. In addition, 1–3 × 10¹¹ W are given to the complex system of the Birkeland currents: about 4 × 10¹⁰ of this, on the average, goes to parallel acceleration, chiefly of auroral electrons, about 2–3 times that amount to joule heating of the ionosphere, and the rest heats the ring current. The ring current stores energy (mainly as kinetic energy of particles) of the order of 2 × 10¹⁵ J, and this value rises and decays during magnetic storms, on time scales ranging from a fraction of a day to several days. The tail can store comparable amounts as magnetic energy, and appreciable fractions of its energy may be released in substorms, on time scales of tens of minutes. The sporadic power level of such events reaches the order of 3 × 10¹² W. The role of magnetic merging in such releases of magnetic energy is briefly discussed, as is the correlation between properties of the solar wind and magnetospheric power levels.     

Multiple Beam Satellite System Optimization

An analytical method is developed for determining the basic RF link parameters that are required in a satellite system design. Certain simplifying assumptions are required and specific system elements are selected. Two different design criteria are considered; optimizing the per-beam signal energy to noise spectral density ratio (Eb/N0), and minimizing the per-user costs. These two criteria are complements of each other subject to coverage and performance constraints. The model can be used to rapidly assess tradeoffs in various system elements. A specific example of a domestic satellite system is considered. The economic analyses are also considered and the economy of scale effect is demonstrated for the design example and considered.     

Changes in the loco-regional Cerebral Blood Flow (r.C.B.F.) during a simulation of weightlessness.

Experiments of prolonged bedrest in antiorthostatic position are conducted in order to simulated cardio-circulatory modifications observed in weightlessness. Until now, no studies of r.C.B.F. have been effected in these conditions. Six young, healthy volunteers (average age 23.8) were placed in strict bedrest and in antiorthostatic position -4 degrees for 7 days. The r.C.B.F. measurements were studied by 133Xe inhalation method using a 32 detectors system. Studies were made first in basal conditions, then between the 6th and 12th hr, and finally between the 72nd and the 78th hr after the beginning of the experiment. Three of the subjects received 0.450 mg of Clonidine daily during the experiment. In the subjects having taken no Clonidine, we observed a constant increase in r.C.B.F. (12, 17 and 16% respectively) in the first 12 hr; at the 72nd hour, all values had returned to basal state. This findings agrees with the well known notion of a rapid correction of hemodynamic disturbances observed in the first days of weightlessness. In the subjects treated with Clonidine, the increase of r.C.B.F. did not occur. Several mechanisms of action are possible; the Clonidine affecting either the heart by inhibiting volemic atrial receptors or the brain by direct vasoconstriction.     

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