Sensor validation using hardware-based on-line learning neuralnetworks

The objective of this document Is to show the capabilities of parallel hardware-based on-line learning neural networks (NNs). This specific application is related to an on-line estimation problem for sensor validation purposes. Neural-network-based microprocessors are starting to be commercially available. However, most of them feature a learning performed with the classic back-propagation algorithm (BPA). To overcome this lack of flexibility a customized motherboard with transputers was implemented for this investigation, The extended BPA (EBPA), a modified and more effective BPA, was used for the on-line learning, These parallel hardware-based neural architectures were used to implement a sensor failure detection, identification, and accommodation scheme in the model of a night control system assumed to be without physical redundancy in the sensory capabilities. The results of this study demonstrate the potential for these neural schemes for implementation in actual flight control systems of modern high performance aircraft, taking advantage of the characteristics of the extended back-propagation along with the parallel computation capabilities of NN customized hardware     

The Impact of Strong Scintillation on Space Based Radar Design II: Noncoherent Detection

Electromagnetic signals that propagate through strongly disturbed regions of the ionosphere can experience scattering which can cause significant amplitude, phase, and angle-of-arrival fluctuations. This paper considers the performance of a space based radar (SBR) that must operate through a highly disturbed propagation environment such as might occur during a barium release or after a high altitude nuclear detonation. A brief summary of the propagation channel characteristics is given in terms of quantities that are important to SBR design issues. Results are then given showing the effect of noncoherent integration on target detection performance. Both coherent and noncoherent detection performance can be seriously degraded by scintillation if scintillation is not adequately considered in the radar design.     

An Analysis of Wide-Band Microwave Monopulse Direction-Finding Techniques

This paper presents the concept, theory of operation, characteris tic equations, and error analysis of four wide-band monopulse techniques. The basic techniques described, which include pure amplitude monopulse, phase and amplitude monopulse (two-and three-channel configurations), and pure phase monopulse interferometer, are particularly applicable to monopulse direction finding systems that require frequency coverage over several octaves and open-loop angle bearing of several degrees. Sufficient detail and working formulas are included to permit a trade-off analysis to be made between the direction-finding techniques for selection in specific hardware applications.     

How to evidence Primitive Life on an exo-Planet? — The DARWIN project

We report the concept of an IR observatory, with interferometric rejection, to search for Primitive Life on an extra-Solar Planet which has been proposed to the European Space Agency.     

Review of Radiation Damage to Silicon Solar Cells

This paper reviews a large number of silicon solar cell irradiation experiments performed over the last 10 years, including 1-MeV and energy spectrum electron studies, and low-(100-keV) and high-energy (up to 155-MeV) proton studies on bare and covered silicon solar cells of several types. The results of satellite flight experiments on individual solar cells are also presented, as well as data from complete solar arrays and data on the new high-efficiency solar cells. Experimental evidence indicates that the percentage of degradation is smaller in thin solar cells than in thick ones, and that cells with high resistivity (10 ?·cm) degrade less than cells with lower resistivity (1 ?·cm). It is shown that high-efficiency silicon solar cells produced at COMSAT Laboratories and pilot production groups of these cells retain most of their increased power output under irradiation. It is emphasized that all surfaces and edges of the solar cells must be completely shielded from the large flux protons in the space environment. Insufficiencies in the published data are noted in certain areas, and recommendations for additional research are presented. Finally, an extensive bibliography is included.     

On the origin of satellite swarms

For a species to develop in nature basically two things are needed: an enabling technology and a “niche”. In spacecraft design the story is the same. Both a suitable technology and a niche application need to be there before a new generation of spacecraft can be developed. In the last century two technologies have emerged which had and still have a huge impact on the development of technical systems: Micro-Electronics (ME) and Micro-Systems Technology (MST). Many different terrestrial systems have changed dramatically since the introduction of ME and MST and many new systems have emerged. In the same period many nano-satellites have been built and launched and shown that they can perform in space. Still it is not clear what the specific role of these small satellites will be. Where will they go? What will they do? In this paper the authors will try to answer these questions and will refer to the OLFAR space born radio telescope as one of the niche applications for a nano-satellite swarm.     

Solar particle event dose distributions: parameterization of dose-time profiles

Calculations of total dose and dose equivalent as a function of time since the start of the event are presented for four of the major solar particle events that occurred during the period from August to December 1989. Results are presented for exposures to the skin, ocular lens and bone marrow shielded by a nominal thickness of aluminum shielding, comparable to that provided by a spacesuit. The calculated curves of organ dose and dose equivalent versus time are parameterized using a Weibull functional form for the fitting equation. The fitting parameters are determined using least squares regression techniques. These results provide a useful starting point for the development of methods to predict the cumulative doses and times to reach various dose limits from a limited number of dose measurements early in a solar particle event.