Three-axis attitude determination via Kalman filtering of magnetometer data

A three-axis Magnetometer/Kalman Filter attitude determination system for a spacecraft in low-altitude Earth orbit is developed, analyzed, and simulation tested. The motivation for developing this system is to achieve light weight and low cost for an attitude determination system. The extended Kalman filter estimates the attitude, attitude rates, and constant disturbance torques. Accuracy near that of the International Geomagnetic Reference Field model is achieved. Covariance computation and simulation testing demonstrate the filter's accuracy. One test case, a gravity-gradient stabilized spacecraft with a pitch momentum wheel and a magnetically-anchored damper, is a real satellite on which this attitude determination system will be used. The application to a nadir pointing satellite and the estimation of disturbance torques represent the significant extensions contributed by this paper. Beyond its usefulness purely for attitude determination, this system could be used as part of a low-cost three-axis attitude stabilization system

Autonomous Magnetic Navigation for Earth Orbiting Spacecraft

The strength and orientation of the Earth\u27s magnetic field varies as a function of the location of the observations, which means that the magnetic field measurements contains position information. Many artificial satellites carry a magnetometer on-board. The local magnetic field measurements could be used to provide navigation information. Such a navigation method has the advantage of requiring only data from low cost on-board instruments and has applications in low budget operation of satellite systems. Furthermore if processing can be performed on-board, this method leads to the possibility of fully autonomous long term navigation. In many systems magnetic navigation could be an effective back-up. To study the feasibility and potential performance of spacecraft magnetic navigation, the concept was investigated using two possible approaches. In a first configuration the magnetic field orientation is assumed to be complemented by measurements of the Nadir direction provided by an Earth horizon sensor on board; the two vectors form the basis of a space sextant. In the second configuration magnetic field magnitude is the sole source of external information

Active Magnetic Control System for Gravity Gradient Stabilized Spacecraft

Active magnetic control is studied as a means to improve the capabilities and performance of gravity gradient stabilized spacecraft. Active magnetic control eliminates the need for a passive damper and can reduce significantly the costs and complexity of other functional parts of the spacecraft. The system under study includes three magnetic torquers, one three-axis magnetometer, and a control processor. It does not require any moving parts, and provides for rapid libration damping, tighter stabilization and active control of the yaw angle. Control algorithms are defined. Results of the analysis of the control laws and computer simulations, including high-order models of the geomagnetic field and atmospheric disturbance torques, are presented. The algorithms perform well within a wide range of orbital inclinations and attitude angles and allow maneuverability and stabilization around the yaw axis. A Kalman Filter is used to provide estimates of the attitude angles, the angular rates, and a global disturbance torque, based on measurements from the magnetometer. Results of simulations, including the attitude estimator in the control loop, are presented. The possibility of a fully autonomous acquisition, deployment, and stabilization sequence using the magnetic control system is discussed

The Space System for the High Energy Transient Experiment

The High Energy Transient Experiment (HETE) is an astrophysics project funded by NASA and led by the Center for Space Research (CSR) at the Massachusetts Institute of Technology (MIT). It has for principal goal the detection and precise localization of the still mysterious sources of gamma ray bursts. The project is original in many respects. HETE will provide simultaneous observations of bursts in the gamma, X-ray and UV ranges from the same small (250 Ibms) space platform. A network of ground stations around the world will diffuse in real time key information derived from HETE observations to many ground observatories, allowing quick follow-on observations with ground instruments. The whole project is entirely managed by MIT, under top level NASA supervision, and satellite and ground stations will be remotely operated from CSA. The HETE system development is conducted with a small budget and under a short schedule

Remote Access Observatories in Low Earth Orbit -A Low-Cost Concept for a Small Scientific Spacecraft

In parallel with the evolution of large observatory spacecraft such as the Einstein, Copernicus, and IUE, and the yet-to-be-Iaunched Hubble Space Telescope and Gamma Ray Observatory, Increasingly large ground telescopes are in construction which will allow ground astronomy to compete favorably with elaborate and expensive space systems in the quest for new discoveries. Sometimes overlooked in this pursuit of new discoveries, with the limited observational time on the space Instruments, or the oversubscribed large ground Instruments, Is the recent development of smaller, low-cost robotic ground observatories designed for routine - but vital - collection of synoptic data. High-quality stellar observations are now being made by exploitation of new computer and detector technologies in unattended remote ground observatories, typically by modest aperture Instruments tailored to the Job. These Instruments operate in modes similar to those employed in the observatory spacecraft. Recent developments In the small satellite technology, some being reported at this conference, allow a reduced cost of payload delivery Into orbit and suggest that another look Is deserved at the 1960s\u27 concept of small astronomical satellites, which would be operable by simple command systems to conduct monitoring of variable, flare, and cataclysmic stars, perhaps limited only to precision filter photometry or simple Imaging In wavelengths not accessible from the ground. These would allow conduct of bread-and-butter astronomy at and accuracies wavelengths available only In space on objects Identified by the larger research Instruments, undertaking science too costly to pursue over long periods with multi-billion dollar systems. This paper will explore small spacecraft provided with low-cost attitude systems (LCAS) for stabilization, modest telescope optics, and low-power communications and spacecraft computer sub-systems which could perform autonomous celestial acquisitions and photometric data collection

Effects of fro and HzO on andesite phase relations between 2 and 4 kbar

International audienceExperimentalp hasee quilibriah ave been investigatedo n three medium-K silicic andesite (60-61 wt % SiO2) samples from Mount Pelhe at 2-4 kbar, 850-1040øC, under both vapor-saturatedC O2-freea nd vapor-saturatedC O2-bearingc onditions.M ost experiments were crystallizatione xperimentsu singd ry glassesp reparedf rom the naturalr ocks.B oth normal-a nd rapidq uenche xperimentsw ere performed.T wo rangeso f oxygenf ugacity( fo2) were investigatedN: NO (Ni-NiO buffer) to NNO + 1 and NNO + 2 to NNO + 3. At 2 kbar for moderatelyo xidizing conditionsp, lagioclase( pl) and magnetite( mt) are the liquidus phases, followed by low-Ca pyroxene (opx); these three phases coexist over a large temperature( T)-H20 range( 875-950øC and 5-7 wt % H20 in melt). Amphibole (am) is stable undern ear vapor-saturatedC O2-freec onditionsa t 876øC. At 900øC, ilmenite (ilm) is found only in experimentsle sst hano r equalt o NNO. Upon increasingp ressure( P) underv aporsaturatedC O2-freec onditionsp, l + mt is replacedb y am + mt on the liquidusa bove3 .5 kbar. For highly oxidizingc onditionsm, t is the solel iquidusp hasea t 2 kbar, followed by pl and opx, except in the most H20-rich part of the diagram at 930øC, where opx is replaced by Carich pyroxene( cpx) and am. Compositionso f ferromagnesianp hasess ystematicallyc orrelate with changingfo2E xperimentalg lassesr angef rom andesitict hroughd acitict o rhyolitic, showings ystematicc ompositionavl ariationsw ith pl + opx + mt fractionation( increaseo f SiO2a ndK 20,d ecreasoef A1203C, aO,F eOt, andM gO).F eO*/MgOm oderateilnyc reases with increasingS iO2.F orfo2 conditionst ypical of calk-alkalinem agmatism( approximately NNO + 1), magnetite is either a liquidus or a near-liquidus phase in hydrous silicic andesite magmas,a nd this shoulds timulater eexaminationfo r the mechanismso f generationo f andesitesb y fractionationf rom basalticp arents

Barrett's esophagus: clinical features, obesity, and imaging

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87127/1/j.1749-6632.2011.06044.x.pd

Design of Group IIA Secreted/Synovial Phospholipase A2 Inhibitors: An Oxadiazolone Derivative Suppresses Chondrocyte Prostaglandin E2 Secretion

Group IIA secreted/synovial phospholipase A2 (GIIAPLA2) is an enzyme involved in the synthesis of eicosanoids such as prostaglandin E2 (PGE2), the main eicosanoid contributing to pain and inflammation in rheumatic diseases. We designed, by molecular modeling, 7 novel analogs of 3-{4-[5(indol-1-yl)pentoxy]benzyl}-4H-1,2,4-oxadiazol-5-one, denoted C1, an inhibitor of the GIIAPLA2 enzyme. We report the results of molecular dynamics studies of the complexes between these derivatives and GIIAPLA2, along with their chemical synthesis and results from PLA2 inhibition tests. Modeling predicted some derivatives to display greater GIIAPLA2 affinities than did C1, and such predictions were confirmed by in vitro PLA2 enzymatic tests. Compound C8, endowed with the most favorable energy balance, was shown experimentally to be the strongest GIIAPLA2 inhibitor. Moreover, it displayed an anti-inflammatory activity on rabbit articular chondrocytes, as shown by its capacity to inhibit IL-1β-stimulated PGE2 secretion in these cells. Interestingly, it did not modify the COX-1 to COX-2 ratio. C8 is therefore a potential candidate for anti-inflammatory therapy in joints