A new type of magnetic gimballed momentum wheel and its application to attitude control in space

A new type of magnetically suspended gimbal momentum wheel utilizing permanent magnets is described. The bearing was composed of four independent thrust actuators which control the rotor thrust position and gimbal angles cooperatively, so that the bearing comes to have a simple mechanism with high reliability and light weight. The high speed instability problem due to the internal damping was easily overcome by introducing anisotropic radial stiffness. A momentum flywheel with the 3-axis controlled magnetic bearing displays good performance for attitude control of satellite with biased momentum.     

Solar orbiter, a high-resolution mission to the sun and inner heliosphere

The scientific rationale of the Solar Orbiter is to provide, at high spatial (35 km pixel size) and temporal resolution, observations of the solar atmosphere and unexplored inner heliosphere. Novel observations will be made in the almost heliosynchronous segments of the orbits at heliocentric distances near 45 R and out of the ecliptic plane at the highest heliographic latitudes of 30° – 38°. The Solar Orbiter will achieve its wide-ranging aims with a suite of sophisticated instruments through an innovative design of the orbit. The first near-Sun interplanetary measurements together with concurrent remote observations of the Sun will permit us to determine and understand, through correlative studies, the characteristics of the solar wind and energetic particles in close linkage with the plasma and radiation conditions in their source regions on the Sun. Over extended periods the Solar Orbiter will deliver the first images of the polar regions and the side of the Sun invisible from the Earth.     

Regional in situ validation of satellite altimeters: Calibration and cross-calibration results at the Corsican sites

The in situ validation of the satellite altimeter sea surface heights is generally performed either at a few local points directly flown over by the satellites or using the global tide gauge network. A regional in situ calibration method was developed by NOVELTIS in order to monitor the altimeter data quality in a perimeter of several hundred kilometres around a given in situ calibration site. The primary advantage of this technique is its applicability not only for missions flying over dedicated sites but also for missions on interleaved or non repetitive orbits. This article presents the altimeter bias estimates obtained with this method at the Corsican calibration site, for the Jason-1 mission on its nominal and interleaved orbits as well as for the Jason-2 and Envisat missions. The various regional bias estimates (8.2 cm and 7.4 cm for Jason-1 respectively on the nominal and interleaved orbits in Senetosa, 16.4 cm for Jason-2 in Senetosa and 47.0 cm for Envisat in Ajaccio, with an accuracy between 2.5 cm and 4 cm depending on the mission) are compared with the results obtained by the other in situ calibration teams. This comparison demonstrates the coherency at the centimetre level, the stability and the generic character of the method, which would also be of benefit to the new and future altimeter missions such as Cryosat-2, SARAL/AltiKa, Sentinel-3, Jason-3, Jason-CS.     

Chirp Waveform Generation Using Digital Samples

This paper describes two methods of generating an analog frequency-modulated waveform by the use of a small number of digital samples of the ?chirp? waveform. The number of digital samples required is a function of the time-bandwidth product. For certain values of time-bandwidth product, this type of signal generation becomes extremely efficient. Several proofs are offered which show how to select ?optimum? values of time-bandwidth products. Two hardware implementations are suggested. One is based on the use of modulo arithmetic and a small stored memory table. The second method utilizes the inherent signal symmetries available if ?optimum? time-bandwidth products are selected. The symmetrical signal patterns are stored in recirculating reversible shift registers which can be read out at high speeds.     

Lithium-ion cell performance under environmental extremes

High energy density, lithium secondary cells are very attractive for use in many future military applications. However, a number of technical challenges remain. Specifically, the development and qualification of a system capable of withstanding the harsh environmental conditions encountered during normal and abnormal zones of operation. This paper focuses on the environmental extremes that the Eagle-Picher lithium-ion system has tested to date. Emphasis is placed on low temperature performance, high temperature performance, power capability, and cycle life at these extremes. Other areas including safety and environmental issues have also been investigated     

Advanced measurement of rotor vibration in electric drives

The combination of microelectronic acceleration transducers and an RF telemetry link can provide a reliable means of measuring shaft vibrations of electric drives. Clear advantages include the possibility of installing the instrumentation into currently existing motor systems without any need to use flexible couplings or mounts. The proposed system covers frequencies up to several kilohertz and can handle torque transients of 20 Nm with a typical uncertainty of 1%. The preliminary system is extendable to cover adaptive control of dynamic drive performance and can be customized to specific speed and torque ranges     

Morgan phenomenon unravels the mysteries of the Universe

We readily convince ourselves that most achievements can be credited to the construction of powerful jet engines, which enable a spaceship to escape gravity. The principle of jet propulsion seems to work perfectly; jet engines can accelerate a rocket up to an incredible speed of 11 km/sec. Looks like there is nothing left to desire. However, from the physical point of view, 11 km/sec is not such a large value compared, for instance, to the speed of light. Would it be possible to attain half of that speed using gas jets? Unfortunately, the answer is no. Nevertheless, that is not the end of the story. The purpose of this article is to show that it is still possible to use the same principle to remove limitations on attainable speed if instead of gas jets, we employ ultrafast electron beams. The basic idea of our construction was inspired by the paper by H. Morgan (ibid., vol. 13, pp. 5-10, 1998). In that article he experimentally refuted the common premise that nothing can go faster than light and gave some theoretical arguments supporting his experimental data. Although the nature and underlying principles of the Morgan phenomenon are yet to be understood, we can already start thinking of its practical applications     

The Origin and Evolution of the Asteroid Belt��Implications for Vesta and Ceres

Vesta and Ceres are the largest members of the asteroid belt, surviving from the earliest phases of Solar System history. They formed at a time when the asteroid belt was much more massive than it is today and were witness to its dramatic evolution, where planetary embryos were formed and lost, where the collisional environment shifted from accretional to destructive, and where the current size distribution of asteroids was sculpted by mutual collisions and most of the asteroids originally present were lost by dynamical processes. Since these early times, the environment of the asteroid belt has become relatively quiescent, though over the long history of the Solar System the surfaces of Vesta and Ceres continue to record and be influenced by impacts, most notably the south polar cratering event on Vesta. As a consequence of such impacts, Vesta has contributed a significant family of asteroids to the main belt, which is the likely source of the HED meteorites on Earth. No similar contribution to the main belt (or meteorites) is evident for Ceres. Through studies of craters, the surfaces of these asteroids will offer an opportunity for Dawn to probe the modern population of small asteroids in a size regime not directly observable from Earth.     

Methods for Characterising Microphysical Processes in Plasmas

Advanced spectral and statistical data analysis techniques have greatly contributed to shaping our understanding of microphysical processes in plasmas. We review some of the main techniques that allow for characterising fluctuation phenomena in geospace and in laboratory plasma observations. Special emphasis is given to the commonalities between different disciplines, which have witnessed the development of similar tools, often with differing terminologies. The review is phrased in terms of few important concepts: self-similarity, deviation from self-similarity (i.e. intermittency and coherent structures), wave-turbulence, and anomalous transport.     

Investigation of Buckling Behavior for Thin-Walled Bearing Aircraft Structural Elements with Cutouts by Means of Numerical Simulation

In this paper, we develop the consistent mathematical models and appropriate lowconsuming numerical methods for investigating the nonlinear strain and buckling behavior of statically loaded thin-walled structures with cutouts. The numerical simulation allowed us to study the effects of the dimensions of rectangular cutouts on the buckling of cylindrical shells loaded by the external pressure.