An extended Kalman filter for spinning spacecraft attitude estimation

An extended Kalman filter for real-time ground attitude estimation of a gyro-less spinning spacecraft was developed and tested. The filter state vector includes the angular momentum direction, phase angle, inertial nutation angle, and inertial and body nutation rates. The filter solves for the nutating three-axis attitude and accounts for effects due to principle axes offset from the body axes. The attitude is propagated using the kinematics of a rigid body symmetric about the principle spin axis; disturbance torques are assumed to be small. Filter updates consist only of the measured angles between celestial objects (Sun, Earth, etc.) and the nominal spin axis, and the times these angles were measured. Both simulated data and real data from the Dynamics Explorer -A (DE-A) spacecraft were used to test the filter; the results are presented. Convergence was achieved rapidly from a wide range of a priori state estimates, and sub-degree accuracy was attained. Systematic errors affecting the solution accuracy are discussed, as are the results of an attempt to solve for sensor measurement angle biases in the state vector

What can earth tide measurements tell us about ocean tides or earth structure?

Current experimental problems in Earth tides are reviewed using comparisons of tidal gravity and tilt measurements in Europe with loading calculations are examples. The limitations of present day instrumentation and installation techniques are shown as well as some of the ways in which they can be improved. Many of the geophysical and oceanographic investigations that are possible with Earth tide measurements are discussed with emphasis on the percentage accuracies required in the measurements in order to obtain new information about Earth or its oceans

Goddard research and engineering management exercise /GREMEX/

Computer assisted management simulation exercise for training of personnel as project manager

Attraction of migratory inanga (galaxias maculatus) and koaro (galaxias brevipinnis) juveniles to adult galaxiid odours

The response of migratory galaxiid juveniles, inanga (Galaxias maculatus) and koaro (G. brevipinnis), to the odours of adult galaxiids was tested in a two-choice chamber apparatus. Both conspecific and heterospecific odours were tested. Inanga juveniles were attracted to adult inanga (G. maculatus), banded kokopu (G. fasciatus), and koaro (G. brevipinnis) odours. However, they were not attracted to odours from common bullies (Gobiomorphus cotidianus). Koaro juveniles exhibited a species-specific attraction to adult koaro odours only. These results demonstrate inanga uveniles can discriminate and are attracted to adult galaxiids during their migratory phase, whilst migratory koaro juveniles exhibit a species-specific attraction to adult odours similar to the pheromonal attraction previously described for juvenile banded kokopu. This strengthens the hypothesis for the use of pheromonal cues in stream and habitat selection by amphidromous galaxiids

Chiral-symmetry breaking in dual QCD

In the context of the formulation of QCD with dual potentials, we show that chiral-symmetry breaking occurs only in the confined state. Therefore, the transition temperature, beyond which chiral symmetry is restored, is the same as the deconfinement temperature. To carry out the calculation, it is necessary to couple quarks to dual gluons. We indicate how this is done (to lowest order in the magnetic coupling constant) and give the Feynman rules for quark–dual-gluon vertices

Static quark potential according to the dual-superconductor picture of QCD

We use the effective action describing long-range QCD, which predicts that QCD behaves as a dual superconductor, to derive the interaction energy between two heavy quarks as a function of separation. The dual-superconductor field equations are solved in an approximation in which the boundary between the superconducting vacuum and the region of normal vacuum surrounding the quarks is sharp. Further, non-Abelian effects are neglected. The resulting heavy-quark potential is linear in separation at large separation, and Coulomb-like at small separation. Overall it agrees very well with phenomenologically determined potentials

Quantized electric-flux-tube solutions to Yang-Mills theory

We suggest that long-distance Yang-Mills theory is more conveniently described in terms of electric rather than the customary magnetic vector potentials. On this basis we propose as an effective Lagrangian for this regime the most simple gauge-invariant (under the magnetic rather than electric gauge group) and Lorentz-invariant Lagrangian which yields a 1/q^4 gluon propagator in the Abelian limit. The resulting classical equations of motion have solutions corresponding to tubes of color electric flux quantized in units of e/2 (e is the Yang-Mills coupling constant). To exponential accuracy the electric color energy is contained in a cylinder of finite radius, showing that continuum Yang-Mills theory has excitations which are confined tubes of color electric flux. This is the criterion for electric confinement of color