Modeling Atmospheric and Solar Radiation Pressure Effects on the Attitude Dynamics of Small Satellites

Because of the current interest in: 1) Small inexpensive LEO satellites, 2) Small STS/SS tethered satellites, and 3) Precision pointing spacecraft used in celestial and terrestrial observations, there is a renewed interest in predicting the effects of solar and atmospheric pressures on these vehicles. To date the majority of published work has been restricted to simple, well defined vehicle geometries. The investigation of other geometries requires a considerable effort to redefine and implement the new configuration. Since it is difficult, if not impossible, to find a near optimal spacecraft geometry analytically, the designer must choose a particular configuration and limit the number of modifications made to it because of the tremendous expenditure of time and money. Additionally, the very difficult task of assessing solar and atmospheric pressure torques due to shadowing is almost nonexistent in the literature. It has long been known that these nonlinear shadowing effects are an important consideration for stability analysis of a particular design. Because of the difficulty in modeling, they have been dealt with in one of two ways; either simple step jumps in torque magnitude have been considered when a surface has become shadowed or unshadowed, or the effects are neglected entirely. Neither of these approaches is desirable, rather a piecewise continuous function would be preferred in which partial shadowing of a surface is considered

AeroAstro’s Escort – A Microsatellite for On-Orbit Inspection of Space Assets

The recent tragic loss of the Space Shuttle Columbia highlights the need for the independent, in-situ inspection of operational satellites. To address this problem, AeroAstro has been designing an autonomous companion microsatellite named Escort™. Given the extremely high value of major operational satellites, AeroAstro believes that responsible stakeholders should insist on having a relatively low-cost Escort-like microsatellite accompanying their satellites. Other critical roles that Escort can fill include on-orbit inspection of a technology validation satellite, situational awareness of the “space neighborhood” around another satellite, and even aiding the deployment and periodic calibration of another satellite. Each Escort is intended to perform proximity operations around a much larger satellite after either releasing itself from its host or after being delivered to the vicinity of the target satellite by a transfer vehicle. Once near the primary satellite, Escort can maneuver autonomously or in a supervised manner, either to inspect from any angle and distance or to hibernate. AeroAstro is in the process of developing a variety of bus and payload technologies to enable the Escort concept. AeroAstro’s patented RF Probe, in particular, can be used as a highly sophisticated diagnostic inspection tool to measure emissions from a communications satellites on-orbit

Operation of a Small Tethered Payload

This paper presents results of a study currently being performed at Stanford University sponsored by NASA/Goddard Space Station Small Attached Payloads. The use of tethers as a means of dynamic isolation for small attached payloads shows promise in reducing orbital maneuvering vehicle requirements to service co-orbiting facilities while still providing a stable contamination-free platform for precision pointing instruments. Thethers may also be used as a means of deorbiting small sample return vehicles. These return vehicles might be dedicated small experiment carriers for a specific mission and require little manned interaction, or they might be loaded with experimental samples for de-orbit and reentry. Another application lies in electrodynamic tether research for ionospheric and vehicle charging and potential studies to continue the effort initiated with the Space Shuttle Tethered Satellite System. The study focuses on defining the issues and resource requirements for small tethered payloads. Areas highlighted include attachment and structural interfaces, communication and data handling facilities, power and electrical interfaces, and dynamics and proximity operations issues

A Human Subject Evaluation of Airport Surface Situational Awareness Using Prototypical Flight Deck Electronic Taxi Chart Displays

The advent of Instrument Landing Systems has allowed aircraft to safely takeoff and land in low visibility conditions. However, the lack of a means by which pilots can safely navigate on the ground in poor visibility conditions has been the cause of many runway incursions and several fatal aircraft accidents. Currently flight crews use paper chart depictions of the airport surface and out-the-window visual cues to navigate on the surface. In addition they can be provided some feedback about their position on the surface from ATC. In clear, daylight environmental conditions flight crews can correlate airport features and navigation signs from the out-the-window view with the chart features to maintain airport surface situational awareness. In conditions of fog and darkness however, out-the-window cues are less available and it becomes a difficult task for flight crews to maintain situational awareness. Low visibility conditions also prevent ATC from tracking aircraft position on the airport surface from the tower

Strain Typing Methods and Molecular Epidemiology of Pneumocystis Pneumonia

Several typing methods, with different strengths and weaknesses, are available for studies of Pneumocystis pneumonia

Existe-t-il un réel équilibre entre prévention du terrorisme et le respect des droits et libertés fondamentaux ?

La lutte contre le terrorisme occupe aujourd'hui plus que jamais une place importante. La première réaction fut le renforcement de l'arsenal répressif, mais dans l'objectif de mener une lutte toujours plus efficace, l'accent fut également mis sur la prévention de l'infraction terroriste. Cela met en évidence une véritable tension entre sécurité et respect des droits et libertés fondamentaux, d'où notre question "existe-t-il un réel équilibre entre la prévention du terrorisme et le respect des droits et libertés fondamentaux ?". Cette contribution n'a pas pour ambition d'analyser l'ensemble des mesures prises dans le cadre de la prévention du terrorisme, mais plutôt de se concentrer sur le sort des libertés et droits fondamentaux à l'égard de certaines mesures préventives que constituent le système PNR, la base de donnée Eurodac, le système de la Blacklist et les mesures de gel de fonds, adoptées et mises en œuvre au niveau européen, ainsi que l'impact de ces mesures sur le droit belge.Master [120] en droit, Université catholique de Louvain, 201