A Diagnostic Tree Approach for Fault Cause Identification in the Attitude Control Subsystem of Satellites

Space and Earth observation programs demand stringent guarantees ensuring smooth and reliable operations of space vehicles and satellites. Due to unforeseen circumstances and naturally occurring faults, it is desired that a fault-diagnosis system be capable of detecting, isolating, identifying, or classifying faults in the system. Unfortunately, none of the existing fault-diagnosis methodologies alone can meet all the requirements of an ideal fault- diagnosis system due to the variety of fault types, their severity, and handling mechanisms. However, it is possible to overcome these shortcomings through the integration of different existing fault-diagnosis methodologies. In this paper, a novel learning-based, diagnostic-tree approach is proposed which complements and strengthens existing efficient fault detection mechanisms with an additional ability to classify different types of faults to effectively determine potential fault causes in a subsystem of a satellite. This extra capability serves as a semiautomatic diagnostic decision support aid to expert human operators at ground stations and enables them to determine fault causes and to take quick and efficient recovery/reconfiguration actions. The developed diagnosis/analysis procedure exploits a qualitative technique denoted as diagnostic tree (DX-tree) analysis as a diagnostic tool for fault cause analysis in the attitude control subsystem (ACS) of a satellite. DX-trees constructed by our proposed machine-learning-based automatic tree synthesis algorithm are demonstrated to be able to determine both known and unforeseen combinations of events leading to different fault scenarios generated through synthetic attitude control subsystem data of a satellite. Though the immediate application of our proposed approach would be at ground stations, the proposed technique has potential for being integrated with causal model-based diagnosis and recovery techniques for future autonomous space vehicle missions.     

SVSS: Intelligent video surveillance system for aircraft

Safety and security are the most discussed topics in the aviation field. The latest security initiatives in the field of aviation propose [1I] the aircraft carriers to implement video surveillance within the aircraft at strategic locations. The current proposals allow the video surveillance data to be stored within the aircraft and monitored by one of the flight crew. The monitoring crew will be responsible for identifying the anomaly within the aircraft and take necessary preventive actions. With the introduction of additional technology within the aircraft, mere human perception may not be sufficient to make a decision. In this research work, the authors explore the possibility of implementing a smart video surveillance system (SVSS) within the aircraft that is tuned toward detecting the behavioral anomaly within the aircraft. The SVSS will generate security triggers when it detects an anomaly within the aircraft. These triggers could be combined with other triggers generated by different aircraft components (possible alarms from the flight crew, data traffic anomaly, or alarm generated by one of the avionics components) to provide a better understanding of the situation to the monitoring crew.     

Early history of cosmic rays and solar wind – Some personal remembrances

The early history of solar wind was replete with prejudices and strong opposition to Parker’s formulation. It was only after conclusive evidence from satellite data was obtained that the idea of solar wind was accepted. Some personal experiences of mine during my stay at the University of Chicago in 1953–1954, including the encounter of Dr. Simpson with Dr. Biermann and the inconclusive discussion between them about a possible perpetual solar outflow of particles are presented and further developments when Parker came to Chicago in 1956 and formulated his idea of solar wind, as narrated to me later by Dr. Simpson, are described.     

CWLFM Radar for Ship Detection and Identification

Continuous wave lineal frequency modulated (CWLFM) radar presents some interesting advantages for coast surveillance and control as well as low probability of interception (LPI). This paper presents real results obtained with a radar prototype and processed with ISAR techniques. Also, results of an automatic ship identification system applied to simulated ISAR images are exposed. Moreover, radar behavior with unfavorable meteorological conditions is discussed     

Quality management for space systems in ISRO

In a little over four decades, the Indian Space Program has carved a niche for itself with the unique application driven program oriented towards National development. The end-to-end capability approach of the space projects in the country call for innovative practices and procedures in assuring the quality and reliability of space systems. The System Reliability (SR) efforts initiated at the start of the projects continue during the entire life cycle of the project encompassing design, development, realisation, assembly, testing and integration and during launch. Even after the launch, SR groups participate in the on-orbit evaluation of transponders in communication satellites and camera systems in remote sensing satellites. SR groups play a major role in identification, evaluation and inculcating quality practices in work centres involved in the fabrication of mechanical, electronics and propulsion systems required for Indian Space Research Organization's (ISRO's) launch vehicle and spacecraft projects. Also the reliability analysis activities like prediction, assessment and demonstration as well as de-rating analysis, Failure Mode Effects and Criticality Analysis (FMECA) and worst-case analysis are carried out by SR groups during various stages of project realisation. These activities provide the basis for project management to take appropriate techno-managerial decisions to ensure that the required reliability goals are met. Extensive test facilities catering to the needs of the space program has been set up. A system for consolidating the experience and expertise gained for issue of standards called product assurance specifications to be used in all ISRO centres has also been established.     

Characterization of the near Earth radiation environment by Liulin type spectrometers

Comprehensive study of the dose, flux and deposited energy spectra shape data obtained by Liulin type spectrometers on spacecraft (five different experiments) and aircraft since 2001 is performed with the aim of understanding how well these parameters can characterize the type of predominant particles and their energy in the near Earth radiation environment. Three different methods for characterisation of the incoming radiation from Liulin spectrometers are described. The results revealed that the most informative one is by the shape of the deposited energy spectra. Spectra generated by Galactic Cosmic Rays (GCR) protons and their secondaries are with linear falling shape in the coordinates deposited energy/deposited per channel dose rate. The position of the maximum of the deposited energy spectra inside the South Atlantic Anomaly (SAA) region depends on the incident energy of the incoming protons. Spectra generated by relativistic electrons in the outer radiation belt have a maximum in the first channels. For higher energy depositions these spectra are similar to the GCR spectra. Mixed radiation by protons and electrons and/or bremsstrahlung is characterized by spectra with 2 maxima. All type of spectra has a knee close to 6.2 MeV deposited energy, which correspond to the stopping energy of protons in the detector. Dose to flux ratio known also as specific dose is another high information parameter, which is given by experimentally obtained formulae [Heffner, J. Nuclear radiation and safety in space. M. Atomizdat. 115, 1971 (in Russian)] connecting the dose to flux ratio and the incident energy of the particles.     

Investigation of helicopter maneuverability by the power balance method

The algorithms for calculating available overloads and maneuvers are presented. Nesterov’s loop maneuver is analyzed.     

Simulating Electrical Faults within Future Aircraft Networks

There is a growing need for accurate and time efficient modelling of electrical distribution networks within the aerospace industry, for which power electronic converters are an integral part. Simplifying converter models is necessary to improve simulation execution times, however many existing techniques do not necessarily give accurate results for all types of system level studies. This paper describes an alternative modelling approach to these, which provides accurate results and reduced simulation times for studies of electrical fault analyses.     

Alternative statements of optimal load-bearing structure design problems

We analyze the well-known statements of optimal design problems for load-bearing maximum rigidity structures in which a principle of the minimum of total potential energy of structure deformation is used. A version of the generalized statement of optimization problems for processes described by linear equations with a symmetric operator is proposed. On the basis of the version outlined, we present a mathematical algorithm for obtaining beam structures of maximum rigidity, in which the finite element method is used to solve an analytical problem. We give the numerical results of solving two problems of optimal design of maximum rigidity structures that are simulated by cantilever and statically indeterminate beams.     

The coronal dynamics imagers for the KuaFu mission

The Space Weather Explorer – KuaFu mission will provide simultaneous, long-term, and synoptic observations of the complete chain of disturbances from the solar atmosphere to the geospace. KuaFu-A (located at the L1 liberation point) includes Coronal Dynamics Imagers composed of a Lyman-α coronagraph (from 1.15 to 2.7 solar radii) and a white light coronagraph (out to 15 solar radii), in order to identify the initial sources of Coronal Mass Ejections (CMEs) and their acceleration profiles. The difficulty of observing the lower corona should not be underestimated since instrumental stray light remains a critical issue in the visible because of the low contrast of the corona with respect to the Sun. Observing the corona in the Lyman-α line is a valid alternative to white light observations. This approach takes advantage of both the intrinsic higher contrast of the corona with respect to the solar disk in this line compared to the visible, and the absence of F-corona at 121.6 nm. Furthermore, it has been convincingly shown that the coronal structures seen in Lyman-α correspond to those seen in the visible and which result from Thomson scattering of the coronal ionized gas. This is because the plasma is still collisional in the lower corona so that the hydrogen neutral atoms are coupled to the protons. A classical, all-reflecting internally-occulted Lyot coronagraph is required so as to preserve the image quality down to the inner limit of the field-of-view. A narrow band interference filter located in a collimated beam allows isolating the Lyman-α line. The visible coronagraph will adopt the approach of a single instrument having a large field-of-view extending from 2.5 to 15 solar radii. Such a design is based on refractive externally-occulted coronagraphs built for recent past missions, essentially the LASCO-C2 and C3 instruments and the SECCHI/COR 2 of the STEREO mission, which is itself a combination of the C2 and C3 instruments.