Modeling of the radiation exposure during the flight of the second Bulgarian cosmonaut on board the Mir Space Station.

An experiment involving active detection of space radiation was carried out in the Space Research Institute (SRI) of Bulgarian Academy of Sciences, in preparation of the flight of the second Bulgarian cosmonaut. The radiations that would be encountered on the flight were modelled including solar and galactic cosmic rays and the particle radiation in the Earth's radiation belts. The dose rate was calculated for these different radiations behind the shielding of the space station. The variations in dose rates over the period of the flight were calculated and compared with measurements made during the orbit of the Mir Space Station. The calculated and measured dose rates agreed within 15-35%.     

Joint probabilistic data association for autonomous navigation

A new autonomous navigation scheme based on the joint probabilistic data association (JPDA) approach that processes landmark detections in the field of view (FOV) of an on-board sensor is developed. These detections-some true, some false-are associated to a set of stored landmarks and used to update the state of the vehicle. The results obtained from Monte Carlo simulations prove the ability of this navigation filter to perform in very high false alarm environments. In the different environmental conditions tested in the simulations, the performance of the JPDA navigation filter (JPDANF) is very close to that of the filter based on perfect data association. The very efficient cluster decomposition algorithm presented for the purpose of the navigation problem can also be used in many multitarget tracking applications     

New progress on space solar telescope

The design of the Space Solar Telescope (phase B) has been completed. The telescope system has been manufactured (phase C) since the beginning of 1999, and it will be assembled by the end of 2000. In this paper, mainly the optical design, technique and manufacture will be described. The launch is planned for the summer of 2004.     

Surface emitting lasers for avionics applications

Vertical cavity surface emitting lasers offer many features that are suitable for applications in optical interconnect, optical data bus, optical backplane, and optical signal processing. The authors describe basic device structure and fabrication techniques of GaAs-based vertical cavity surface emitting lasers and discuss key laser performance characteristics such as emission wavelength, beam pattern, threshold current, power output, quantum efficiency, and modulation response that are important to these potential applications. Results on monolithic integration of the laser with an n-channel MESFET driver are described     

Gravity-dependent reactions of the moss Pohlia nutans protonemata.

In darkness, protonemata of Pohlia nutans (Hedw.) grew negatively gravitropically (upwards). However, not all filaments became gravitropic immediately after transfer to darkness. Some of them (~20%) for several days grew in different directions with respect to gravity. The apical cells of those protonemata predominantly contained multiple chloroplasts. The intensity of chlorophyll fluorescence rapidly decreased in the apical cells of such protonemata while starch content increased in comparison with upright growing protonemata. Light, especially in the red and blue part of the spectrum, inhibited protonemal gravitropism. Red light induced stronger inhibitory effects than blue light. Red light of 1.0 to 1.5 micromoles m-2 s-1 intensity induced bud differentiation in apical cells on almost all side branches of main protonemal filaments. Bright fluorescence of F-actin bundles in the tip of apical protonematal cells and a delicately fluorescing network enclosing plastids basal to the tip in a sedimentation zone were visualized. Bright fluorescence of actin as local patches and fine prominent axially oriented bundles was observed in cells of gametophore buds.     

A model of solar energetic particles for use in calculating LET spectra developed from ONR-604 data.

A model of solar energetic particles (SEP) has been developed and is applied to solar flares during the 1990/1991 CRRES mission using data measured by the University of Chicago instrument, ONR-604. The model includes the time-dependent behavior, heavy-ion content, energy spectrum and fluence, and can accurately represent the observed SEP events in the energy range between 40 to 500 MeV/nucleon. Results are presented for the March and June, 1991 flare periods.     

Optimal sensor selection strategy for discrete-time stateestimators

A novel sensor selection strategy is introduced, which can be implemented on-line in time-varying discrete-time system. We consider a case in which several measurement subsystem are available, each of which may be used to drive a state estimation algorithm. However, due to practical implementation constraints (such as the ability of the on-board computer to process the acquired data), only one of these subsystems can actually by utilized at a measurement update. An algorithm is needed, by which the optimal measurement subsystem to be used is selected at each sensor selection epoch. The approach described is based on using the square root V-Lambda information filter as the underlying state estimation algorithm. This algorithm continuously provides its user with the spectral factors of the estimation error covariance matrix, which are used in this work as the basis for an on-line decision procedure by which the optimal measurement strategy is derived. At each sensor selection epoch, a measurement subsystem is selected, which contributes the largest amount of information along the principal state space direction associated with the largest current estimation error. A numerical example is presented, which demonstrates the performance of the new algorithm. The state estimation problem is solved for a third-order time-varying system equipped with three measurement subsystem, only one of which can be used at a measurement update. It is shown that the optimal measurement strategy algorithm enhances the estimator by substantially reducing the maximal estimation error     

HXMT satellite for space hard X-ray observation

In this paper, the Hard X-ray Modulation Telescope mission is introduced. Its primary objective is to perform the hard X-ray all sky survey of high resolution and high sensitivity. The expected angular resolution and position accuracy of the satellite are better than 10^′ and 2^′, respectively. The preliminary mission design is analyzed. And a new attitude subsystem scheme is presented to meet the high precision demand of attitude determination. A conclusion is drawn that the mission design is feasible. The possible launch of it will significantly advance the astrophysical study.     

VLSI architecture for SAR data compression

As a step towards a real-time signal aperture radar (SAR) correlator, custom very large scale integration (VLSI) architectures are developed. Considering the extremely short word length of the data, we derive three architectures with massive parallelism in bit space. Unlike frequency methods, no. degradation is introduced during convolution. Optimized for time and space, they are highly suited to VLSI implementation, and a small architecture with 80 taps operating at 10 MHz has been built using an FPGA