Power law distribution in statistics of failures in operation of spacecraft onboard equipment

The possibility of using the statistics of recurrence time for extreme events is studied in this paper having in mind the problems of control and prediction of failures in spacecraft operation. The information about failures onboard satellites of various types presented by the US National Geophysical Data Center was analyzed. It was found that the probability density of recurrence intervals followed a power law of the Pareto type with an index equal to 2.3. The obtained result is consistent both with the theory of normal catastrophes and with the principle of self-organization of criticality for metastable active heterogeneous environment. A practical consequence of the obtained result consists in the fact that predictions of these extreme events should not rely on traditional models with the second-order Pearson statistics. To make predictions, the models are necessary that take into account the power law distribution of recurrence intervals for failures on satellites. The failures should be considered in these models as extreme events connected with manifestation of the space environment factors.     

Adaptive boosting for SAR automatic target recognition

The paper proposed a novel automatic target recognition (ATR) system for classification of three types of ground vehicles in the moving and stationary target acquisition and recognition (MSTAR) public release database. First MSTAR image chips are represented as fine and raw feature vectors, where raw features compensate for the target pose estimation error that corrupts fine image features. Then, the chips are classified by using the adaptive boosting (AdaBoost) algorithm with the radial basis function (RBF) network as the base learner. Since the RBF network is a binary classifier, the multiclass problem was decomposed into a set of binary ones through the error-correcting output codes (ECOC) method, specifying a dictionary of code words for the set of three possible classes. AdaBoost combines the classification results of the RBF network for each binary problem into a code word, which is then "decoded" as one of the code words (i.e., ground-vehicle classes) in the specified dictionary. Along with classification, within the AdaBoost framework, we also conduct efficient fusion of the fine and raw image-feature vectors. The results of large-scale experiments demonstrate that our ATR scheme outperforms the state-of-the-art systems reported in the literature     

A mathematical model of vibration combustion in a tube with sudden cross-section change

The theoretical study of vibration combustion using a model of the pulsejet engine was carried out. The frequencies and amplitudes of gas vibrations that were calculated by the energy method are well agreed with experimental data.     

An investigation into instrumental nonlinear effects

High order spectral techniques are one of the most powerful tools for the identification of non-linear processes in space plasma turbulence. Without such tools it is impossible to determine, for example, the occurrence of non-linear interactions between spectral components. However, since the observations made by an instrument involve some internal processing, it is possible that non-linearities may arise from within the instrument itself rather than in the plasma. The possibility of such effects are investigated using data resulting from tests carried out using the Cluster Wideband electric field instrument.     

Unusually high geomagnetic activity in 2003

In 2003, geomagnetic activity was found to be considerably higher than in any other year of the current solar cycle. This was caused by the time coincidence of large low-latitude coronal holes and a significant burst of the flare and eruptive activity of the Sun. The features of recent intensification of the activity are discussed, and the long-period behavior of indices of the geomagnetic activity in the 23rd and previous cycles is compared. The large magnetic storms in October–November 2003 are analyzed in more detail.Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 563–573.Original Russian Text Copyright © 2004 by Belov, Gaidash, Ivanov, Kanonidi.     

Space Interferometry Mission instrument model and astrometric performance validation

The Space Interferometry Mission (SIM), performed very accurate astrometric measurements to measure the positions of stars using a 10 m baseline optical interferometer. The lack of signal from the science targets precludes using the star as a feedback signal to control the science interferometer delay line. In order to solve this problem SIM uses pathlength feed forward (PFF) control of the science interferometer. In the case of controlling the science interferometer optical path, the information to position the science delay line comes from a combination of internal metrology, external metrology, and guide interferometer measurements. The accuracy of the internal and external metrology measurements and the guide interferometer measurements are important for the quality of the feed forward signal and also for the ultimate astrometric performance of the instrument. An instrument model of SIM has been built to evaluate optical performance and to emulate various observational scenarios. The effect of averaging methods to reduce metrology cyclic error and the viability of on-orbit calibration maneuvers are studied. The model consists of a real-time dynamics formulation of the spacecraft and a real-time attitude control system. Simulation results investigate the sensitivity of the feed forward signal to the various error sources and time-varying terms.     

Gravitropism in cut flower stalks of snapdragon.

The negative gravitropic response of cut flower stalks is a complex multistep process that requires the participation of various cellular components acting in succession or in parallel. The process was particularly characterized in snapdragon (Antirrhinum majus L.) spikes with regard to (1) gravity stimulus perception associated with amyloplast reorientation; (2) stimulus transduction mediated through differential changes in the level, action and related genes of auxin and ethylene and their possible interaction; (3) stimulus response associated with differential growth leading to stalk curvature; (4) involvement of cytosolic calcium and actin cytoskeleton. Results show that the gravity-induced amyloplast reorientation, differential over-expression of two early auxin responsive genes and asymmetrical distribution of free IAA are early events in the bending process. These precede the asymmetrical ethylene production and differential stem growth, which was derived from initial shrinkage of the upper stem side and a subsequent elongation of the lower stem side. Results obtained with various calcium- and cytoskeleton-related agents indicate that cytosolic calcium and actin filaments may play essential roles in gravitropism-related processes of cut flower stalks. Therefore, modulators of these two physiological mediators may serve as means for controlling any undesired gravitropic bending.     

Main characteristics of biological components of developing life support system observed during the experiments aboard orbital complex MIR.

Since 1990, the orbital complex MIR has witnessed several incubator experiments for determination of spaceflight effects on embryogenesis of Japanese quail. First viable chicks who had completed the whole embryological cycle in MIR microgravity hatched out in 1990; it became clear that newborns would not be able to adapt to microgravity unaided. There were 8 successful incubations of chicks in the period from 1990 to 1999. In 1995-1997 the MIR-NASA space science program united Russian and US investigators. As a result, experiments Greenhouse-1 and 2 were performed with an effort to grow super dwarf wheat from seed to seed, and experiment Greenhouse-3 aimed at receiving two successive generations of Brassica rapa. But results of these experiments could not be used for definitive conclusions concerning effects of spaceflight on plant ontogenesis and, therefore, experiments Greenhouse-4 and 5 were staged within the framework of the Russian national space program. The experiments finally yielded wheat seeds. Some of the seeds was left on the space station and, being planted, gave viable seedlings which, in their turn, produced the second crop of space seeds.     

Evaluation of built-in test

Built-in test (BIT) provides fault finding as a means to aid in system assembly, test, and maintenance. An investigation to evaluate BIT of a particular electronics board used in the in-flight entertainment system for Boeing 777s is described. We found BIT proved useful when failure occurrences were uniquely associated with the operating environment, situations which can result in no-fault found, or could-not duplicate (CND) failures upon test. We also observed cases where the BIT failed to observe failures, and in some cases pointed to the wrong cause of failure. These and other advantages and disadvantages of BIT implementation are discussed