The Scanning Sky Monitor (SSM) on ASTROSAT

The Scanning Sky Monitor is one of the experiments onboard the ASTROSAT, an Indian multiwavelength astronomy satellite mission. This experiment will detect and monitor X-ray transients in the energy band 2–10 keV. It is similar in design to the ASM on RXTE. It consists of position-sensitive proportional counters with one-dimensional mask. We describe the configuration of the experiment. We also discuss some of the results obtained using a detector which has already been fabricated and tested in our laboratory.     

Information Support for Space Experiments Based on a Numerical-Analytical Theory of Satellite Motion

A software tool for application in calculations of the position and velocity vectors of spacecraft is presented. These vectors are necessary at the stage of processing the data of space experiments and analyzing the results of ground-based observations. A new theory of satellite motion, in a numerical-analytical form, is the basis of this software application. The model of disturbing forces corresponds to recommendations of the International Laser Ranging Service. The reliability of the software tool is confirmed by the results of processing of high-precision laser satellite observations.     

Variable frequency switching in power supply EMI-control: an overview

Spreading the signal spectrum is a widely used technique in telecommunication applications. Variable-frequency and spread spectrum modulation methods can also be utilized in power electronic applications to improve electro-magnetic compatibility (EMC). This paper gives an overview to variable-frequency techniques in power electronics with experimental results.     

Cognitive deficits induced by 56Fe radiation exposure.

Exposing rats to particles of high energy and charge (e.g., 56Fe) disrupts neuronal systems and the behaviors mediated by them; these adverse behavioral and neuronal effects are similar to those seen in aged animals. Because cognition declines with age, and our previous study showed that radiation disrupted Morris water maze spatial learning and memory performance, the present study used an 8-arm radial maze (RAM) to further test the cognitive behavioral consequences of radiation exposure. Control rats or rats exposed to whole-body irradiation with 1.0 Gy of 1 GeV/n high-energy 56Fe particles (delivered at the alternating gradient synchrotron at Brookhaven National Laboratory) were tested nine months following exposure. Radiation adversely affected RAM performance, and the changes seen parallel those of aging. Irradiated animals entered baited arms during the first 4 choices significantly less than did controls, produced their first error sooner, and also tended to make more errors as measured by re-entries into non-baited arms. These results show that irradiation with high-energy particles produces age-like decrements in cognitive behavior that may impair the ability of astronauts to perform critical tasks during long-term space travel beyond the magnetosphere.     

Battery charger design for the Columbus MTFF power system

A novel pulsewidth-modulated (PWM) dc-dc converter topology is proposed for the battery charge regulator (BCR) of the Columbus Man-Tended Free-Flyer (MTFF) power system. The system is a regulated bus system. Bus voltage control is implemented at the input of the BCR. The use of a conventional buck topology with PWM conductance control at the input results in a second-order behavior. A study of new PWM dc-dc converter topologies has been made to attain a suitable topology. The proposed converter topology is designed and a breadboard including the control loop has been built and tested. The experimental results show that the converter operates according to the design constraints.     

Image texture synthesis-by-analysis using moving-average models

A synthesis-by-analysis model for texture replication or simulation is presented. This model can closely replicate a given textured image or produce another image that although distinct from the original, has the same general visual characteristics and the same first and second-order gray-level statistics as the original image. The texture synthesis algorithm, proposed contains three distinct components: a moving-average (MA) filter, a filter excitation function, and a gray-level histogram. The analysis portion of the texture synthesis algorithm derives the three from a given image. The synthesis portion convolves the MA filter kernel with the excitation function, adds noise, and modifies the histogram of the result. The advantages of this texture model over others include conceptually and computationally simple and robust parameter estimation, inherent stability, parsimony in the number of parameters, and synthesis through convolution. The authors describe a procedure for deriving the correct MA kernel using a signal enhancement algorithm, demonstrate the effectiveness of the model by using it to mimic several diverse textured images, discuss its applicability to the problem of infrared background simulation, and include detailed algorithms for the implementation of the model     

A (design-oriented) reliability model for active phased arrays insatellite communication systems

This paper proposes a modeling approach to relate the power section reliability of satellite payloads to the on-board antenna complexity. The aim of the model is to support the development of design tools for satellite systems adopting active phased arrays. The achieved results are rendered parametric with respect to a key system requirement, the effective isotropic radiated power, due to its direct impact on transmitter configuration and technological features as well as on the critical compromise between transmitter and antenna specifications     

A fault-tolerant air data/inertial reference unit

The fault-tolerant air data/inertial reference unit (ADIRU) described is a key part of a fault-tolerant air data/inertial reference system (ADIRS) designed to be the inertial and air data reference for the ARINC 651 Integrated Modular Avionics (IMA) distributed architecture. The ADIRU has been designed to meet the commercial aviation market demands for low life cycle cost and high integrity fault detection, fault isolation, and redundancy management. The ADIRU's internal redundant resources provide quad channel redundancy that is one level higher than conventional triple redundant systems, allowing it to provide deferred maintenance capability. Robust partitioning, simple serial internal interfaces, and simple voting planes ensure that internal redundant components are properly utilized to provide high integrity system outputs. This relieves systems using it from having to perform their own redundancy management of the air data and inertial outputs from multiple sources required by conventional systems     

A two-dimensional position-sensitive spectroscopic proportional counter for balloon-borne hard X-ray astronomy

A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc.