Study of the rheological properties of water and Martian soil simulant mixtures for engineering applications on the red planet

The rheological properties of mixtures of water and the Martian soil simulant JSC-Mars-1A are investigated by preparing and testing samples at various solids concentrations. The results indicate that the dispersion is viscoelastic and, at small timescales (～0.1?s), reacts to sudden strain as an elastic solid. At longer timescales the dispersion behaves like a Bingham fluid and exhibits a yield stress. Hysteresis loops show that rapid step-changes (2?s duration) of shear-rate result in thixotropic behaviour, but slower changes (>10?s duration) can result in rheopexy. These observations are explained with the breakdown and recovery of the packing structure under stress. The rheological information is used to generate practical tools, such as the system curve and the Moody chart that can be used for designing piping systems, and calculating pump sizes and pressure requirements.     

Stochastic modelling considering ionospheric scintillation effects on GNSS relative and point positioning

Global Navigation Satellite Systems (GNSS), in particular the Global Positioning System (GPS), have been widely used for high accuracy geodetic positioning. The Least Squares functional models related to the GNSS observables have been more extensively studied than the corresponding stochastic models, given that the development of the latter is significantly more complex. As a result, a simplified stochastic model is often used in GNSS positioning, which assumes that all the GNSS observables are statistically independent and of the same quality, i.e. a similar variance is assigned indiscriminately to all of the measurements. However, the definition of the stochastic model may be approached from a more detailed perspective, considering specific effects affecting each observable individually, as for example the effects of ionospheric scintillation. These effects relate to phase and amplitude fluctuations in the satellites signals that occur due to diffraction on electron density irregularities in the ionosphere and are particularly relevant at equatorial and high latitude regions, especially during periods of high solar activity. As a consequence, degraded measurement quality and poorer positioning accuracy may result.     

Keeping Ma’at: An astronomical approach to the orientation of the temples in ancient Egypt

For various reasons, Archaeoastronomy has not been one of the favourite disciplines of the Egyptologists in the past. Probably because of that, important questions such as the orientation of Egyptian temples and the relevance of astronomy in this respect had never been afforded with the necessary seriousness and deepness. The Egyptian–Spanish Mission for the Archaeoastronomy of ancient Egypt has, among its various priorities, the solution of this problem. In order to achieve that, we have measured the orientation of some 330 temples in the Valley, the Delta, the Oases and the Sinai so far. The aim is to find a correct and almost definitive answer to the question of whether the ancient Egyptian sacred constructions were astronomically aligned or not. Our data seem to answer this question in the affirmative sense. Besides, they offer a very interesting new perspective in the field of landscape archaeology, a new discipline hardly worked in Egypt so far, in which terrestrial landscape, dominated by the Nile, and celestial landscape, dominated by the sun and the stars, would combine in order to permit the establishment of Ma’at, the Cosmic Order, on Earth.     

Data and performances of selected aircraft and rotorcraft

The purpose of this article is to provide a synthetic and comparative view of selected aircraft and rotorcraft (nearly 300 of them) from past and present. We report geometric characteristics of wings (wing span, areas, aspect-ratios, sweep angles, dihedral/anhedral angles, thickness ratios at root and tips, taper ratios) and rotor blades (type of rotor, diameter, number of blades, solidity, rpm, tip Mach numbers); aerodynamic data (drag coefficients at zero lift, cruise and maximum absolute glide ratio); performances (wing and disk loadings, maximum absolute Mach number, cruise Mach number, service ceiling, rate of climb, centrifugal acceleration limits, maximum take-off weight, maximum payload, thrust-to-weight ratios). There are additional data on wing types, high-lift devices, noise levels at take-off and landing. The data are presented on tables for each aircraft class. A graphic analysis offers a comparative look at all types of data. Accuracy levels are provided wherever available.     

Cubesats: Cost-effective science and technology platforms for emerging and developing nations

The development, operation, and analysis of data from cubesats can promote science education and spur technology utilization in emerging and developing nations. This platform offers uniquely low construction and launch costs together with a comparative ubiquity of launch providers; factors that have led more than 80 universities and several emerging nations to develop programs in this field. Their small size and weight enables cubesats to “piggyback” on rocket launches and accompany orbiters travelling to Moon and Mars. It is envisaged that constellations of cubesats will be used for larger science missions. We present a brief history, technology overview, and summary of applications in science and industry for these small satellites. Cubesat technical success stories are offered along with a summary of pitfalls and challenges encountered in both developed and emerging nations. A discussion of economic and public policy issues aims to facilitate the decision-making process for those considering utilization of this unique technology.     

Transmit Beamforming for MIMO Radar Systems using Signal Cross-Correlation

Proposed next-generation radar systems will have multiple transmit apertures with complete flexibility in the choice of the signals transmitted at each aperture. Here we propose the use of multiple signals with arbitrary cross-correlation matrix R, and show that R can be chosen to achieve or approximate a desired spatial transmit beampattern. Two specific problems are addressed. The first is the constrained optimization problem of finding the value of R which causes the true transmit beampattern to be close in some sense to a desired beampattern. This is approached using convex optimization techniques. The second is the problem of designing multiple constant-modulus waveforms with given cross-correlation R. The use of coded binary phase shift keyed (BPSK) waveforms is considered. A method for finding the code sequences based on random signaling with a structured correlation matrix is proposed. It is also shown that by restricting the class of admissible waveforms one reduces the set of possible signal correlation matrices.     

Microsatellite Laser Altimeter

A feasibility study is presented of a laser altimeter conceived as an auxiliary device of an imaging camera to perform stereo pairs correction by high accuracy range measurements. System configuration is compliant to microsatellite constraints and is integrated to a high-resolution imaging sensor. System performance analysis is carried out by means of analytical models and computer codes and plots are presented to select key parameters allowing definition of a preliminary laser altimeter configuration     

Towards a One Percent Measurement of Frame Dragging by Spin with Satellite Laser Ranging to LAGEOS, LAGEOS 2 and LARES and GRACE Gravity Models

During the past century Einstein’s theory of General Relativity gave rise to an experimental triumph; however, there are still aspects of this theory to be measured or more accurately tested. Today one of the main challenges in experimental gravitation, together with the direct detection of gravitational waves, is the accurate measurement of the gravitomagnetic field generated by the angular momentum of a body. Here, after a brief introduction on frame-dragging, gravitomagnetism and Lunar Laser Ranging tests, we describe the past measurements of frame-dragging by the Earth spin using the satellites LAGEOS, LAGEOS 2 and the Earth’s gravity models obtained by the GRACE project. We demonstrate that these measurements have an accuracy of approximately 10%. We then describe the LARES experiment to be launched in 2010 by the Italian Space Agency for a measurement of frame-dragging with an accuracy of a few percent. We finally demonstrate that a number of claims by a single individual, that the error budget of the frame-dragging measurements with LAGEOS-LAGEOS 2 and LARES has been underestimated, are indeed ill-founded.