Simulation of gemini-agena docking

Attitude and translation control using visual docking simulator for Gemini/Agena projec

Analytical Investigation of the Reentry Behavior of the ''flying Wind Tunnel'' Test Vehicle, with Some Effects of Threshold and Torque Level of a Roll-rate Control System

Analytical investigation of reentry behavior of flying wind tunnel test vehicle with some effects of threshold and torque level of roll-rate control syste

Limnologie et télédétection : situation actuelle et développements futurs

La télédétection satellitaire est un outil employé couramment et avec succès en océanographie. Il n'en va pas de même en limnologie, où les applications sont encore rares.Par le moyen d'une revue bibliographique, nous tentons d'en analyser les raisons. Après une brève description de l'outil et des satellites en service, l'on met en évidence la spécificité des cibles aquatiques, caractérisées par une réflectance basse et une profondeur d'investigation variable. Ces particularités, jointes à la composition complexe des eaux intérieures, rendent impossible l'extension pure et simple, à la limnologie, des algorithmes développés en océanographie.Néanmoins, nous montrons que la télédétection a été utilisée dans l'étude du bassin versant des lacs, ainsi que pour la cartographie de leurs limites, de la végétation aquatique, des courants, de la thermique et de la couleur de l'eau. Des modèles empiriques, exprimant la matière en suspension ou les paramètres de qualité de l'eau, ont été calculés et appliqués avec succès dans certains lacs.On établit ensuite une typologie des difficultés rencontrées dans l'application de la télédétection à la limnologie : intrinsèques (complexité de la composition), technologiques (capteurs actuels non adaptés aux cibles aquatiques) et institutionnels (coûts élevés et manque de professionnels de ta télédétection dans les cercles limnologiques).Finalement, l'on présente quelques propositions pratiques dans la perspective des nouveaux véhicules spatiaux et capteurs des années 90, qui devraient permettre une exploitation de l'énorme potentiel de la télédétection en limnologie.Remote sensing has been used successfully in oceanography for many years, whereas applications in limnology have been comparatively modest. We attempt to discover why from a review of the literature.After a brief description of remote sensing and of satellites in operation, we stress the specificity of inland waters targets compared with "solid" targets : low reflectivity in the visible and near infrared, complex water composition (chlorophyll, mineral suspensoids and gelbstoff which are not covariant) and the variable depth of investigation. Hence, simple chlorophyll and suspended solid retrieval algorithms, developed for type-I waters, cannot be applied to inland waters.Nonetheless, remote sensing may be, and has been applied effectively to the study and management of drainage basins and to the mapping of lake limits, aquatic vegetation, water masses, currents, thermal structures and water colour. Site-specific, regression-type models have been computed to express suspended solid concentration and water quality parameters as functions of radiante. So far, most of the applications have been performed on large lakes (Laurentian Great Lakes, Tahoe, Chad, Biwa, Balaton, Léman), where not only LANDSAT but also CZCS and AVHRR data have been in operation.A typology of present difficulties in applying remote sensing to limnology is proposed : intrinsic (complexity of inland waters), technological (land resource satellite bands not designed for water sensing, revisit time too long) and institutional difficulties (cost of data and equipment, and scarcity of limnologists proficient in remote sensing techniques)

Aerodynamic Characteristics at a Mach Number of 3.10 of Several Fourth-Stage Shapes of the Scout Research Vehicle

A wind-tunnel investigation was made at a Mach number of 3.10 (Reynolds number per foot of 16.3 x 10(exp 6) to 16.9 x 10(exp 6)) to determine the aerodynamic characteristics of various modifications of the payload section of the fourth stage of the Scout research vehicle. It was found that, for the combination of stages 3 and 4, increasing the size of the nose of the basic Scout to provide a cylindrical section of the same diameter as the third stage increased the normal-force slope by about 30 percent, the axial force by about 39 percent, and moved the center of pressure forward by about one fourth-stage base diameter. By reducing the diameter of the cylinder, at about one nose length behind the base of the enlarged nose frustum, to that of the basic Scout and thereafter retaining the shape of the basic Scout, the center of pressure was moved rearward by about one-half fourth-stage base diameter at the expense of an additional 19-percent increase in axial force. A spike-hemisphere configuration had the largest forces and moments and the most forward center-of-pressure location of the configurations considered. Except for the axial force and pitching-moment slope, the experimental trends or magnitudes could not be estimated with the desired accuracy by Newtonian or-slender body theory