Comparison of Two Major Classes of Coherent Pulsed Radar Systems

Two classes of coherent radar types are analyzed to ascertain whether any significant advantages exist for a given system. The classes compared are those coherent radars which transmit a phasecoherent pulse-to-pulse RF carrier as opposed to those which transmit randomly phased RF carriers but store the coherent information at the radar for Doppler extraction. Rigorous new analytical development is avoided in favor of examination of the considerable existing literature, examination of practical limitations, and synthesis of generic solutions from key concepts. Examination is made of coherent radar classes from the viewpoints of reconnaissance ance and intelligence measurement, new radar design and devlopment, and electronic countermeasures vulnerability. The conclusion that the classes of coherent radars examined have a priori and a posteriori equivalent performance has significant implications not published in any reference source.     

A bacterial enrichment study and overview of the extractable lipids from paleosols in the Dry Valleys, Antarctica: implications for future Mars reconnaissance

The Dry Valleys of Antarctica are one of the coldest and driest environments on Earth with paleosols in selected areas that date to the emplacement of tills by warm-based ice during the Early Miocene. Cited as an analogue to the martian surface, the ability of the Antarctic environment to support microbial life-forms is a matter of special interest, particularly with the upcoming NASA/ESA 2018 ExoMars mission. Lipid biomarkers were extracted and analyzed by gas chromatography--mass spectrometry to assess sources of organic carbon and evaluate the contribution of microbial species to the organic matter of the paleosols. Paleosol samples from the ice-free Dry Valleys were also subsampled and cultivated in a growth medium from which DNA was extracted with the explicit purpose of the positive identification of bacteria. Several species of bacteria were grown in solution and the genus identified. A similar match of the data to sequenced DNA showed that Alphaproteobacteria, Gammaproteobacteria, Bacteriodetes, and Actinobacteridae species were cultivated. The results confirm the presence of bacteria within some paleosols, but no assumptions have been made with regard to in situ activity at present. These results underscore the need not only to further investigate Dry Valley cryosols but also to develop reconnaissance strategies to determine whether such likely Earth-like environments on the Red Planet also contain life.     

High resolution solar ultraviolet measurements

The increase of our understanding of the processes acting in the solar corona and maintaining it is strongly dependent on the quality of the data that are obtained to check theories. The fine structure of the solar atmosphere seen from the photosphere and extending to the hottest parts of the corona requires data with high resolution in all parameter space (angular, spectral and temporal). To constrain the hypotheses that are proposed to describe the solar corona, it is necessary to establish an accurate energy budget taking into account the processes which are acting from the chromosphere to the corona. Some requirements can be established and compared with the data collected so far (or about to be collected) with the present SUMER (Solar Utraviolet Measurements of Emitted Radiations) instrumentation.     

Spatial Gauss-Markov Models of Ocean Currents

Ocean currents are an important error source in marine inertial navigation systems (INS). Satellite radar altimeter data are used to construct self- consistent Gauss- Markov models of ocean currents. These models are useful for INS error analysis and optimal (Kalman) filtering of INS outputs.     

Embraer 170/190的维修市场前景

随着北美地区Embraer 170/190双发喷气机机队规模的扩大,各类MRO供应商开始扩展其维修能力,以满足此类机型日益增长的维修需求.     

Ethological analysis of a polar team in the French Antarctic station Dumont d'Urville as simulation of space teams for future interplanetary missions

This new ethological study focuses on the co-adaptation of the crew's spatial behavior to social isolation in a polar base thus simulating long-term living and working of a space team. The method consisted in drawing the subjects' position (n=13) on an observation map at the midday and evening meals at the Dumont d'Urville French station in Antarctica, daily during the summer campaigns and weekly during the winter-over of the TA46 mission. Quantitative data are presented in geocentric (positions), allocentric (distances) and egocentric (orientations) analyses with an emphasis on three adaptative periods (first 3 months, intermediary 2 months and last 3 months of isolation). Results show a large space occupancy during the first week after arrival and the last week before departure from the polar base, and a team-members' grouping during the winter-over. On the over-all time, the inter-individual distances increase. The social orientations are higher at the beginning than at the end of the mission. Discussion underlies the pertinent use of such ethological indicators collected from polar stations as predictors of well-being and optimal-working of the future orbital and planetary stations users.     

Space insurance : Comments from an observer

The space insurance industry has suffered serious financual setbacks in recent years. These setbacks, amounting to a net cash outflow of hundreds of millions of dollars, have resulted in substantial increases in insurance rates and the withdrawal of a number of firms from the launch insurance market. After two decades of commerial space activity a number of questions may be raised: What has been learned from the experience to date? What are the causes of the poor performance of the space insurance industry? What can be done to improve performance? What are the likely prospects of the insurance industry and the likely impacts on the communications satellite industry? In order to answer these questions several examples are considered and analytic approaches discussed. The implications of mission modes, failure/recovery paths and multiple correlated payloads are considered, and analytic approaches based upon computer simulation techniques are described which are required to understand the complex insurance environment and the setting of policies and rate structures.     

Effective radiation reduction in Space Station and missions beyond the magnetosphere.

Presented are results from a parametric study of the shielding effectiveness of low and high atomic number shields on biological dose equivalent for low-earth-orbit and interplanetary manned missions.     

State-Space Models of Gravity Disturbance Gradients

State-space models of gravity disturbance gradients are needed to design the Kalman filters used for gradiometer-aided inertial navigation. However, the physics of the gravity field guarantee that many of the cross-spectral densities of gravity disturbance gradients are nonrational. A procedure is demonstrated for fitting gravity disturbance correlation functions with finite-dimensional state-space models.     

Effects of Geodetic Uncertainties on a Damped Inertial Navigation System

Gravity uncertainties are an inexorable source of error in all inertial navigation systems and are particularly important in high-quality inertial navigation systems. In this paper the steady-state rms errors that are excited in a damped inertial navigation system are analytically determined for four gravity uncertainty models and two vehicle maneuver models. The statistical approach used in this paper is compared with an alternate scheme (?direct simulation?) that does not require statistical models for gravity uncertainties.