The status of qualification of a new separator system for advancedaerospace battery cells

A nickel cadmium cell system which utilizes a polypropylene separator impregnated with polybenzimadazole, and which shows promise of providing an aerospace battery with performance equivalent to Super NiCd, and yet is more cost effective, is described. Background information, cell construction information, detailed test program information and data, and status of qualification are given     

Pattern recognition of star constellations for spacecraftapplications

A software system for a star imager for on-line satellite attitude determination is described. The system works with a single standard commercial CCD-camera with a high aperture lens and an onboard star catalogue. It is capable of both an initial course attitude determination without any prior knowledge of the satellite orientation and a high-accuracy attitude determination based on prediction and averaging of several identified star constellations. In the high accuracy mode the star imager aims at an accuracy better than 2 arc sec with a processing time of less than a few seconds. The star imager is developed for the Danish microsatellite Oersted     

On phased-array radar tracking and parameter control

Based on a simple model of a ground-based phased-array radar used for a multiple-target surveillance task, beam scheduling, positioning, and radar parameters like signal-to-noise ratio, track sharpness, and detection threshold have been optimized with respect to the radar/computer load induced by tracking. From this the minimum energy necessary for track maintenance during surveillance can be derived     

A low-cost space-based radar system concept

A space-based radar system concept is described that can provide continuous world-wide, all-weather, day-night observation and tracking of ships, aircraft, vehicles and ground facilities of interest. The system employs a constellation of radar satellites in low-earth orbit to provide continuous world-wide target access. The radars employ reflector antennas, TWT transmitters and high frequency (e.g., X band) to achieve long range with relatively low weight, complexity and cost. The radars operate in moving-target-detection (MTD) and synthetic-aperture-radar (SAR) spotlight imaging modes to observe moving and fixed targets, respectively. The system could support a wide range of military, intelligence, law-enforcement and civilian missions     

Ambiguity resolution of multiple targets using pulse-Dopplerwaveforms

To cancel clutter, both medium-PRF waveforms which are ambiguous in both range and Doppler and high-PRF waveforms which are ambiguous in range but unambiguous in ambiguities, a previous paper has shown that superior results for a single target can be achieved by using a clustering algorithm. Here, the problem of multiple targets is considered. A maximum likelihood (ML) technique which incorporates the clustering algorithm is developed for the multiple target problem. Simulation results show that four targets which have the same speed but are at different ranges can be resolved by using a medium-PRF waveform and employing the ML resolution technique     

Probing solar and stellar interior dynamics and dynamo

Solar and stellar activity is a result of complex interaction between magnetic field, turbulent convection and differential rotation in a star’s interior. Magnetic field is believed to be generated by a dynamo process in the convection zone. It emerges on the surface forming sunspots and starspots. Localization of the magnetic spots and their evolution with the activity cycle is determined by large-scale interior flows. Thus, the internal dynamics of the Sun and other stars hold the key to understanding the dynamo mechanism and activity cycles. Recently, significant progress has been made for modeling magnetohydrodynamics of the stellar interiors and probing the internal rotation and large-scale dynamics of the Sun by helioseismology. Also, asteroseismology is beginning to probe interiors of distant stars. I review key achievements and challenges in our quest to understand the basic mechanisms of solar and stellar activity.     

Electron density models for the lower ionosphere

Probably the only reliable method of checking an electron density model below 70 km is to calculate from it what would be obtained by VLF or LF propagation over certain paths, and to compare the results with actual observations. This has been done for the IRI at various frequencies from 16 to 70 kHz; the results agree in places but differ substantially elsewhere. Previous models described by the author give satisfactory results and it is suggested that certain features of them might be incorporated with advantage in the IRI. In particular, it is impossible to get agreement with VLF propagation in all seasons by means of a model varying only with solar zenith angle, such as the IRI from 50–90 km.     

Calibration techniques for magnetometers implementing on-board de-spinning algorithms

The Fluxgate Magnetometer experiments on-board the European Space Agency’s four spacecraft Cluster Mission have the capability to store sampled magnetic field vectors in the instrument memory, either as a full resolution ‘event capture’ or as spin-resolution vectors transformed into a non-spinning co-ordinate system (de-spun). The latter capability has ensured a dataset is available which extends the partial orbital coverage achieved during nominal operations in the first years of operation. The on-board de-spin is achieved using a Walsh function with Haar coefficients and allows for up to 27 h additional data per non-coverage interval. A number of commissioning orbits were used to verify the accuracy of data collected by the de-spin mode, whereby individual spacecraft were operated separately in a number of standard normal sampling and de-spin mode combinations. Up to the present time, this data has not been available to the Cluster community. We present results here comparing the performance of the on-board de-spin algorithm versus the normal sampling modes over a number of boundary layer crossings, describe the techniques used for calibration and timeline recovery, and outline the context in which the data may be usable in future studies.     

Free radicals induced in solid DNA by heavy ion bombardment.

Free radical formation after heavy-ion bombardment was studied in solid, polycristalline pellets of DNA-constituents by analysing the dose-yield curves and the spectra obtained by ESR-spectroscopy at low (< 100 K) and ambient temperatures. The dose-yield curves were found to correlate with those found after X-irradiation but shifted to higher doses and lower saturation concentrations. The corresponding radical yields (per 100 eV) exhibit values which are one to two orders of magnitudes lower. The structural aspects as revealed from powder ESR-spectra gave a complex inter-relation between substance, LET, dose and irradiation temperature, which is discussed in terms of mechanistic models.     

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.