10,322 research outputs found
Lessons Learned from the Pioneers 10/11 for a Mission to Test the Pioneer Anomaly
Analysis of the radio-metric tracking data from the Pioneer 10/11 spacecraft
at distances between 20--70 astronomical units (AU) from the Sun has
consistently indicated the presence of an anomalous, small, constant Doppler
frequency drift. The drift is a blue-shift, uniformly changing with rate a_t =
(2.92 +/- 0.44) x 10^(-18) s/s^2. It can also be interpreted as a constant
acceleration of a_P = (8.74 +/- 1.33) x 10^(-8) cm/s^2 directed towards the
Sun. Although it is suspected that there is a systematic origin to the effect,
none has been found. As a result, the nature of this anomaly has become of
growing interest. Here we discuss the details of our recent investigation
focusing on the effects both external to and internal to the spacecraft, as
well as those due to modeling and computational techniques. We review some of
the mechanisms proposed to explain the anomaly and show their inability to
account for the observed behavior of the anomaly. We also present lessons
learned from this investigation for a potential deep-space experiment that will
reveal the origin of the discovered anomaly and also will characterize its
properties with an accuracy of at least two orders of magnitude below the
anomaly's size. A number of critical requirements and design considerations for
such a mission are outlined and addressed.Comment: 11 pages, invited talk given at ``35th COSPAR Scientific Assebly,''
July 18-24, 2004, Paris, Franc
A Pragmatic Approach to DHT Adoption
Despite the peer-to-peer community's obvious wish to have its systems adopted, specific mechanisms to facilitate incremental adoption have not yet received the same level of attention as the many other practical concerns associated with these systems. This paper argues that ease of adoption should be elevated to a first-class concern and accordingly presents HOLD, a front-end to existing DHTs that is optimized for incremental adoption. Specifically, HOLD is backwards-compatible: it leverages DNS to provide a key-based routing service to existing Internet hosts without requiring them to install any software. This paper also presents applications that could benefit from HOLD as well as the trade-offs that accompany HOLD. Early implementation experience suggests that HOLD is practical
A Mission to Test the Pioneer Anomaly
Analysis of the radio tracking data from the Pioneer 10/11 spacecraft has
consistently indicated the presence of an anomalous small Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
The nature of this anomaly has become of growing interest in the fields of
relativistic cosmology, astro- and gravitational physics as well as in the
areas of spacecraft design and high-precision navigation. We present a concept
for a designated deep-space mission to test the discovered anomaly. A number of
critical requirements and design considerations for such a mission are outlined
and addressed.Comment: Final changes for publication. Honorable Mention, 2002 Gravity
Research Foundation Essay
Directly Measured Limit on the Interplanetary Matter Density from Pioneer 10 and 11
The Pioneer 10 and 11 spacecraft had exceptional deep-space navigational
capabilities. The accuracies of their orbit reconstruction were limited,
however, by a small, anomalous, Doppler frequency drift that can be interpreted
as an acceleration of (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed toward the Sun.
We investigate the possibility that this anomaly could be due to a drag on the
spacecraft from their passing through the interplanetary medium. Although this
mechanism is an appealing one, the existing Pioneer radiometric data would
require an unexpectedly high mass density of interplanetary dust for this
mechanism to work. Further, the magnitude of the density would have to be
nearly constant at distances ~ 20-70 AU. Therefore, it appears that such an
explanation is very unlikely, if not ruled out. Despite this, the measured
frequency drift by itself places a directly-measured, model-independent limit
of \lessim 3 x 10^{-19} g/cm^3 on the mass density of interplanetary dust in
the outer(~20-70 AU) solar system. Lower experimental limits can be placed if
one presumes a model that varies with distance. An example is the limit \lessim
6 x 10^{-20} g/cm^3 obtained for the model with an axially-symmetric density
distribution that falls off as the inverse of the distance. We emphasize that
the limits obtained are experimentally-measured, in situ limits. A mission to
investigate the anomaly would be able to place a better limit on the density,
or perhaps even to measure it.Comment: 16 pages, 2 figures, publication versio
The Pioneer Anomaly: The Data, its Meaning, and a Future Test
The radio-metric Doppler tracking data from the Pioneer 10/11 spacecraft,
from between 20-70 AU, yields an unambiguous and independently confirmed
anomalous blue shift drift of a_t = (2.92 \pm 0.44)\times 10^{-18} s/s^2. It
can be interpreted as being due to a constant acceleration of a_P = (8.74 \pm
1.33) \times 10^{-8} cm/s^2 directed towards the Sun. No systematic effect has
been able to explain the anomaly, even though such an origin is an obvious
candidate. We discuss what has been learned (and what might still be learned)
from the data about the anomaly, its origin, and the mission design
characteristics that would be needed to test it. Future mission options are
proposed.Comment: 16 pages, 7 figures, to be published in the AIP Conference
Proceedings of the 2nd Mexican Meeting on Mathematical and Experimental
Physic
The Pioneer Anomaly and Its Implications
The Pioneer 10/11 spacecraft yielded the most precise navigation in deep
space to date. However, their radio-metric tracking data has consistently
indicated the presence of a small, anomalous, Doppler frequency drift. The
drift is a blue-shift, uniformly changing with a rate of ~6 x 10^{-9} Hz/s and
can be interpreted as a constant sunward acceleration of each particular
spacecraft of a_P =(8.74 +/- 1.33) x 10^{-10} m/s^2. The nature of this anomaly
remains unexplained. Here we summarize our current knowledge of the discovered
effect and review some of the mechanisms proposed for its explanation.
Currently we are preparing for the analysis of the entire set of the available
Pioneer 10/11 Doppler data which may shed a new light on the origin of the
anomaly. We present a preliminary assessment of such an intriguing possibility.Comment: 7 pages, 2 figures. Invited talk given at the XXIst IAP Colloquium on
"Mass Profiles and Shapes of Cosmological Structures", Paris, France, July
4-9, 200
Study of the Pioneer Anomaly: A Problem Set
Analysis of the radio-metric tracking data from the Pioneer 10 and 11
spacecraft at distances between 20--70 astronomical units from the Sun has
consistently indicated the presence of an anomalous, small, and constant
Doppler frequency drift. The drift is a blue-shift, uniformly changing at the
rate of (5.99 +/- 0.01) x 10^{-9} Hz/s. The signal also can be interpreted as a
constant acceleration of each particular spacecraft of (8.74 +/- 1.33) x
10^{-8} cm/s^2 directed toward the Sun. This interpretation has become known as
the Pioneer anomaly. We provide a problem set based on the detailed
investigation of this anomaly, the nature of which remains unexplained.Comment: 14 pages, 3 figures, 5 tables, minor corrections before publicatio
If You\u27ve Got the Money, I\u27ve Got the Time: The Benefits of Incentive Contracts with Private Prisons
Governments increasingly rely on private prison companies to manage the daunting demands associated with their ever- increasing prison populations. The private prison industry provides governments at all levels (federal, state, and local) with an alternative to the costly and time-consuming construction of additional public facilities. Governments, however, have all too often adopted a flawed pricing strategy, paying private prison companies fixed per diem rates to house prisoners. This model both incentivized and tolerated poor conditions with greater emphasis placed on the industry\u27s bottom line than benefits to the state, the prison population, or society as a whole.
This article asserts that governments should instead experiment with cost-reimbursement contracts and outcome-based incentives. Re-thinking contract types would encourage governments to engage in strategic, long-term thinking about their goals for prison, appreciating that a rehabilitative model can ultimately save the state money and generate other societal benefits. For example, cost-reimbursement contracts that integrate programs for mental health illnesses or drug and alcohol rehabilitation may ultimately result in a decrease of the next generation\u27s prison population
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