7,035 research outputs found
The Pioneer Anomaly
Radio-metric Doppler tracking data received from the Pioneer 10 and 11
spacecraft from heliocentric distances of 20-70 AU has consistently indicated
the presence of a small, anomalous, blue-shifted frequency drift uniformly
changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was
interpreted as a constant sunward deceleration of each particular spacecraft at
the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of
the Newton's gravitational inverse-square law has become known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. In this review, we
summarize the current knowledge of the physical properties of the anomaly and
the conditions that led to its detection and characterization. We review
various mechanisms proposed to explain the anomaly and discuss the current
state of efforts to determine its nature. A comprehensive new investigation of
the anomalous behavior of the two Pioneers has begun recently. The new efforts
rely on the much-extended set of radio-metric Doppler data for both spacecraft
in conjunction with the newly available complete record of their telemetry
files and a large archive of original project documentation. As the new study
is yet to report its findings, this review provides the necessary background
for the new results to appear in the near future. In particular, we provide a
significant amount of information on the design, operations and behavior of the
two Pioneers during their entire missions, including descriptions of various
data formats and techniques used for their navigation and radio-science data
analysis. As most of this information was recovered relatively recently, it was
not used in the previous studies of the Pioneer anomaly, but it is critical for
the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living
Reviews in Relativit
A Mission to Explore the Pioneer Anomaly
The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of . This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020", 19-21 April 2005, ESTEC,
Noordwijk, The Netherland
The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC
The past decade has seen huge advances in experimental measurements made in
heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more
recently at the Large Hadron Collider (LHC). These new data, in combination
with theoretical advances from calculations made in a variety of frameworks,
have led to a broad and deep knowledge of the properties of thermal QCD matter.
Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created
in these collisions have established that the QGP is a strongly coupled liquid
with the lowest value of specific viscosity ever measured. However, much
remains to be learned about the precise nature of the initial state from which
this liquid forms, how its properties vary across its phase diagram and how, at
a microscopic level, the collective properties of this liquid emerge from the
interactions among the individual quarks and gluons that must be visible if the
liquid is probed with sufficiently high resolution. This white paper, prepared
by the Hot QCD Writing Group as part of the U.S. Long Range Plan for Nuclear
Physics, reviews the recent progress in the field of hot QCD and outlines the
scientific opportunities in the next decade for resolving the outstanding
issues in the field.Comment: 110 pages, 33 figures, 429 references. Prepared as part of the U.S.
Long-Range Plan for Nuclear Physic
Line-of-sight guidance techniques for manned orbital rendezvous
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1963.Vita.Includes bibliographical references (leaves 305-309).by Edwin Eugene Aldrin, Jr.Sc.D
Improving tracking of trajectories through tracking rate regulation: application to UAVs
The tracking problem (that is, how to follow a previously memorized path) is one of the most important problems in mobile robots. Several methods can be formulated depending on the way the robot state is related to the path. âTrajectory trackingâ is the most common method, with the controller aiming to move the robot toward a moving target point, like in a real-time servosystem. In the case of complex systems or systems under perturbations or unmodeled effects, such as UAVs (Unmanned Aerial Vehicles), other tracking methods can offer additional benefits. In this paper, methods that consider the dynamics of the pathâs descriptor parameter (which can be called âerror adaptive trackingâ) are contrasted with trajectory tracking. A formal description of tracking methods is first presented, showing that two types of error adaptive tracking can be used with the same controller in any system. Then, it is shown that the selection of an appropriate tracking rate improves error convergence and robustness for a UAV system, which is illustrated by simulation experiments. It is concluded that error adaptive tracking methods outperform trajectory tracking ones, producing a faster and more robust convergence tracking, while preserving, if required, the same tracking rate when convergence is achieved
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