4,032 research outputs found
Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10
Anderson, et al. find the measured trajectories of Pioneer 10 and 11
spacecraft deviate from the trajectories computed from known forces acting on
them. This unmodelled acceleration (and the less well known, but similar,
unmodelled torque) can be accounted for by non-isotropic radiation of
spacecraft heat. Various forms of non-isotropic radiation were proposed by
Katz, Murphy, and Scheffer, but Anderson, et al. felt that none of these could
explain the observed effect. This paper calculates the known effects in more
detail and considers new sources of radiation, all based on spacecraft
construction. These effects are then modelled over the duration of the
experiment. The model reproduces the acceleration from its appearance at a
heliocentric distance of 5 AU to the last measurement at 71 AU to within 10
percent. However, it predicts a larger decrease in acceleration between
intervals I and III of the Pioneer 10 observations than is observed. This is a
2 sigma discrepancy from the average of the three analyses (SIGMA, CHASMP, and
Markwardt). A more complex (but more speculative) model provides a somewhat
better fit. Radiation forces can also plausibly explain the previously
unmodelled torques, including the spindown of Pioneer 10 that is directly
proportional to spacecraft bus heat, and the slow but constant spin-up of
Pioneer 11. In any case, by accounting for the bulk of the acceleration, the
proposed mechanism makes it much more likely that the entire effect can be
explained without the need for new physics.Comment: Final minor changes for publication - added explanation of acronyms,
added to RTG asymmetry argument.. Was: 12 pages, 9 figures, major revision.
Added discussion of gas leaks and spin history, a radiation based explanation
of spin changes, and references to re-analysis of Markwardt. Fixed radio
forces, tuned models. Was: 7 pages, 5 figures; added liklihood calculations
in body and abstract per suggestio
The Puzzle of the Flyby Anomaly
Close planetary flybys are frequently employed as a technique to place
spacecraft on extreme solar system trajectories that would otherwise require
much larger booster vehicles or may not even be feasible when relying solely on
chemical propulsion. The theoretical description of the flybys, referred to as
gravity assists, is well established. However, there seems to be a lack of
understanding of the physical processes occurring during these dynamical
events. Radio-metric tracking data received from a number of spacecraft that
experienced an Earth gravity assist indicate the presence of an unexpected
energy change that happened during the flyby and cannot be explained by the
standard methods of modern astrodynamics. This puzzling behavior of several
spacecraft has become known as the flyby anomaly. We present the summary of the
recent anomalous observations and discuss possible ways to resolve this puzzle.Comment: 6 pages, 1 figure. Accepted for publication by Space Science Review
Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.Comment: Latex2e, 26 pages, 6 tables, 2 figure, 47 references. It is the
merging of gr-qc/0608127, gr-qc/0608068, gr-qc/0608101 and gr-qc/0611081.
Final version to appear in Foundations of Physic
The Pioneer anomaly: the measure of a topological phase defect of light in cosmology
It is shown that a wave vector representing a light pulse in an adiabatically
evolving expanding space should develop, after a round trip (back and forth to
the emitter) a geometric phase for helicity states at a given fixed position
coordinate of this expanding space.In a section of the Hopf fibration of the
Poincare sphere that identifies a projection to the physically allowed states,
the evolution defines a parallel transported state that can be joined
continuously with the initial state by means of the associated
Berry-Pancharatnam connection. The connection allows to compute an anomaly in
the frequency for the vector modes in terms of the scale factor of the
space-time background being identical to the reported Pioneer Anomaly.Comment: 10 pages, some minor notation changes have been made. Some additional
remarks were writte
If You Can\u27t Stop Them, Protect Them: The Legal Tethers for Bringing Fully Comprehensive Sexual Education Policy to Tennessee
This Note explores why Tennessee needs a comprehensive sexual education curriculum, how Tennessee can get it, and what should be included in the Curriculum. Part II of this Note provides background on sexual health in the United States. Particularly, this section includes statistics surrounding STDs and teen pregnancy, the current sexual health policy in Tennessee, and examples of different sexual education curriculums currently being used throughout the United States. Part III of this Note analyzes legal tethers that can help attain comprehensive sexual education in Tennessee including the Mature Minor Doctrine, Freedom of Religion, the Fourteenth Amendment Liberty Interest, Title IX, and Title V. These anlyses show arguments for comprehensive education and how to overcome the opposition of comprehensive education. Finally, this Note concludes with suggested improvements to Tennessee\u27s Family Life Curriculum policy based off the World Health Organizations International Technical Guidance on Sexual Education and successful comprehensive sexual health curriculums currently being applied in the U.S
The influence of risk perception in epidemics: a cellular agent model
Our work stems from the consideration that the spreading of a disease is
modulated by the individual's perception of the infected neighborhood and
his/her strategy to avoid being infected as well. We introduced a general
``cellular agent'' model that accounts for a hetereogeneous and variable
network of connections. The probability of infection is assumed to depend on
the perception that an individual has about the spreading of the disease in her
local neighborhood and on broadcasting media. In the one-dimensional
homogeneous case the model reduces to the DK one, while for long-range coupling
the dynamics exhibits large fluctuations that may lead to the complete
extinction of the disease
Deformation of the Planetary Orbits Caused by the Time Dependent Gravitational Potential in the Universe
In the paper are studied the deformations of the planetary orbits caused by
the time dependent gravitational potential in the universe. It is shown that
the orbits are not axially symmetric and the time dependent potential does not
cause perihelion precession. It is found a simple formula for the change of the
orbit period caused by the time dependent gravitational potential and it is
tested for two binary pulsars.Comment: 7 page
Towards robust aero-thermodynamic predictions for re-usable single-stage to orbit vehicles
Re-usable single stage to orbit launch vehicles promise to reduce the cost of access to space, but their success will be particularly reliant on accurate and robust modelling of their aero-thermodynamic characteristics. For preliminary design and optimization studies, relatively simple numerical prediction techniques must perforce be used, but it is important that the uncertainty that is inherent in the predictions of these models be understood. Predictions of surface pressure and heat transfer obtained using a new reduced-order model that is based on the Newtonian flow assumption and the Reynolds analogy for heating are compared against those of a more physically-sophisticated Direct Simulation Monte Carlo method in order to determine the ability of the model to capture the aero-thermodynamics of vehicles with very complex configuration even when run at low enough resolution to be practical in the context of design optimization studies. Attention is focused on the high-altitude regime where lifting re-usable Single-Stage to Orbit configurations will experience their greatest thermal load during re-entry, but where non-continuum effects within the gas of the atmosphere might be important. It is shown that the reduced-order model is capable of reproducing the results of the more complex Monte Carlo formalism with surprising fidelity, but that residual uncertainties exist, particularly in the behaviour of the heating models and in the applicability of the continuum assumption given the onset of finite slip velocity on surface of vehicle. The results suggest thus that, if used with care, reduced-order models such as those described here can be used very effectively in the design and optimization of space-access vehicles with very complex configuration, as long as their predictions are adequately supported by the use of more sophisticated computational techniques
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