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Pioneer anomaly
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Title: Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft
Authors: F. Francisco, O. Bertolami, P. J. S. Gil, J. Páramos

We present an improved method to compute the radiative momentum transfer in the Pioneer 10 & 11 spacecraft that takes into account both diffusive and specular reflection. The method allows for more reliable results regarding the thermal acceleration of the deep-space probes, confirming previous findings. A parametric analysis is performed in order to set an upper and lower-bound for the thermal acceleration and its evolution with time.

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Pioneer F
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Pioneer 10 (also known as Pioneer F) was a 258-kilogram robotic space probe launched by NASA on March 2, 1972
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Pioneer 10 anomaly
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Title: Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10
Authors: Louis K. Scheffer
(Version v5)

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.

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RE: Pioneer 10
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Pioneer 10 sends back the first close-up images of Jupiter. (1973)
Pioneer 10 (also called Pioneer F) was the first spacecraft to travel through the asteroid belt, on July 15, 1972, and to make direct observations of Jupiter, which it passed by on December 3, 1973.
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Pioneer anomaly
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A force in space is hindering the journey of a NASA spacecraft.
Scientists have been baffled by a mysterious phenomenon that has prevented the craft from moving further into outer space.
Described as a force that defies all laws of nature, they have said gravity laws may eventually need to be changed.

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RE: Pioneer 10 and 11
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On the 13th June, 1983, Pioneer 10 passed the orbit of Neptune, the outermost planet, and became the first man-made object to leave the solar system.
(Although Pluto was considered to be a planet at the time, it was closer to the Sun than Neptune at that stage due to its highly eccentric orbit passing within that of Neptune.)

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On this day in 2006, the Deep Space Network made a final attempt to contact the Pioneer 10 deep space probe. No response was received.

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PIONEER 10
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PIONEER 10 SPACECRAFT SENDS LAST SIGNAL

After more than 30 years, it appears the venerable Pioneer 10 spacecraft has sent its last signal to Earth.
Pioneer's last, very weak signal was received on Jan. 22, 2003.

NASA engineers report Pioneer 10's radioisotope power source has decayed, and it may not have enough power to send additional transmissions to Earth. NASA's Deep Space Network (DSN) did not detect a signal during the last contact attempt Feb. 7, 2003. The previous three contacts, including the Jan. 22 signal, were very faint with no telemetry received. The last time a Pioneer 10 contact returned telemetry data was April 27, 2002. NASA has no additional contact attempts planned for Pioneer 10.

"Pioneer 10 was a pioneer in the true sense of the word. After it passed Mars on its long journey into deep space, it was venturing into places where nothing built by humanity had ever gone before. It ranks among the most historic as well as the most scientifically rich exploration missions ever undertaken.," - Dr. Colleen Hartman, director of NASA's Solar System Exploration Division, NASA Headquarters, Washington.

"Originally designed for a 21-month mission, Pioneer 10 lasted more than 30 years. It was a workhorse that far exceeded its warranty, and I guess you could say we got our money's worth," - Pioneer 10 Project Manager, Dr. Larry Lasher.
pioneer10.gif
Pioneer 10 was built by TRW Inc., Redondo Beach, Calif., and was launched March 2, 1972, on a three-stage Atlas-Centaur rocket. Pioneer 10 reached a speed of 32,400 mph needed for the flight to Jupiter, making it the fastest human-made object to leave the Earth; fast enough to pass the moon in 11 hours and to cross Mars' orbit, about 50 million miles away, in just 12 weeks.

On July 15, 1972,Pioneer 10 entered the asteroid belt, a doughnut-shaped area that measures some 175 million miles wide and 50 million miles thick. The material in the belt travels at speeds up to 45,000 mph and ranges in size from dust particles to rock chunks as big as Alaska. Pioneer 10 was the first spacecraft to pass through the asteroid belt, considered a spectacular achievement, and then headed toward Jupiter. Accelerating to a speed of 82,000 mph, Pioneer 10 passed by Jupiter on December 3, 1973.

The spacecraft was the first to make direct observations and obtain close-up images of Jupiter. Pioneer also charted the gas giant's intense radiation belts, located the planet's magnetic field, and established Jupiter is predominantly a liquid planet. In 1983, Pioneer 10 became the first human-made object to pass the orbit of Pluto, the most distant planet from the Sun.

Following its encounter with Jupiter, Pioneer 10 explored the outer regions of the solar system, studying energetic particles from the Sun (solar wind), and cosmic rays entering our portion of the Milky Way. The spacecraft continued to make valuable scientific investigations in the outer regions of the Solar System until its science mission ended March 31, 1997.

Since that time,
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Pioneer 10

Pioneer 10's weak signal has been tracked by the DSN as part of a new advanced-concept study of communication technology in support of NASA's future Interstellar Probe mission. At last contact, Pioneer 10 was 7.6 billion miles from Earth, or 82 times the nominal distance between the Sun and the Earth. At that distance, it takes more than 11 hours and 20 minutes for the radio signal, traveling at the speed of light, to reach the Earth.
"From Ames Research Center and the Pioneer Project, we send our thanks to the many people at the Deep Space Network (DSN) and the Jet Propulsion Laboratory (JPL), who made it possible to hear the spacecraft signal for this long," - Pioneer 10 Flight Director David Lozier.
Pioneer 10 explored Jupiter, traveled twice as far as the most distant planet in our solar system, and as Earth's first emissary into space, is carrying a gold plaque that describes what we look like, where we are, and the date when the mission began. Pioneer 10 will continue to coast silently as a ghost ship into interstellar space, heading generally for the red star Aldebaran, which forms the eye of the constellation Taurus (The Bull). Aldebaran is about 68 light-years away. It will take Pioneer 10 more than two million years to reach it. Its sister ship, Pioneer 11, ended its mission September 30, 1995, when the last transmission from the spacecraft was received.
Scientists have discovered

that the Pioneer 10 and 11 space probes, launched more than 30 years ago, appear to be in the grip of a mysterious force that is holding them back as they sweep out of the solar system.
As a result, scientists pressed a European Space Agency (Esa) meeting, called Cosmic Visions, in Paris for a new mission that would follow the Pioneers and pinpoint the cause of their erratic movements. The strange behaviour of the Pioneers was discovered by John Anderson and Slava Turyshev of the Jet Propulsion Laboratory in Pasadena and Michael Martin Neito of the Los Alamos National Laboratory. They noted there were persistent anomalies in their trajectories. Every time they looked the Pioneers were in the wrong place. The effect was not large, but it was significant. One proposal put forward is that Newton's idea that the force of gravity weakens as distance increases may be incorrect over very large spaces, and may drop off over very long distances.
The acceleration of the Pioneer spacecraft could be linked to another anomaly involving apparent gravitation anomalies that were recorded during solar eclipses. According to Chris Duif at the Delft University of Technology, the 'Allais effect' is real, and unexplained.
More detailed information can be found in his paper here. (pdf)
Update:
The Pioneer 10 and 11 spacecraft have had their a small, anomalous, Doppler frequency drift, interpreted as an acceleration, calculated as (8.74 +/- 1.33) x 10-8 cm/s2 towards the Sun
The new study investigated the possibility that this anomaly could be due to a drag on the spacecraft from their passing through a interplanetary medium, but found that the radiometric data would require an unexpectedly high mass density, -19 g/cm3, 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, the researchers found such an explanation to be very unlikely.
A mission to investigate the anomaly would be able to place a better limit on the density, or perhaps even to measure it.


Incidentally, the solar storms of October and November 2003 produced massive coronal mass ejections (CMEs) are about to overtake Voyager 1.
The Voyager 1 spacecraft is nearly 9 billion miles (14.5 billion km) from the sun, at the edge of our solar system.
A solar blast wave is heading for the spacecraft, and "it could arrive at any moment,"
Hopefully, a receiver on board will record a 2 to 3 kHz radio burst .
Voyager 2 measured (indirectly at 600 km/s) the speed of the shock, as well as its composition, temperature and magnetism.

Blast from the pastThe astronomers looking at Pioneer 10's tracking data obtained with the Nasa Deep Space Network, an array of large radio telescopes designed to communicate with far-off space probes, discovered a new object orbiting the Sun after the probe was mysteriously knocked off course.
On 8 December, 1992, when Pioneer 10 was 8.4 billion km away, it was deflected from its predicted course for about 25 days by an unseen object.
This was only the second time in history that a Solar System object has been discovered by its gravitational effect alone.
The planet Neptune was discovered in 1846 after Its position was predicted because of its gravitational tug on the planet Uranus.
The new body, found by a team at Queen Mary and Westfield College in London, UK, and the Jet Propulsion Laboratory in California, is a Kuiper Belt object.
The scientists had been looking for such an effect for years and have analysed the data using several different methods to confirm their findings.

"We are quite excited that we have found one of these events. It is a very neat signal" - Dr Giacomo Giampieri, of Queen Mary and Westfield College.

Pioneer 10 is currently heading towards the stars of the constellation of Taurus, which it will reach in about two million years time.
Nasa has given the go-ahead for the Interstellar Boundary Explorer ( Ibex ) to be built ready for its launch in 2008 from a Pegasus rocket, which will be dropped from the underbelly of a high-altitude airplane.
It will be the first time that a spacecraft will be launched that has the ability to take images of the entire boundary at the very limits of the Solar System.
"This mission will provide a much deeper understanding of the Sun's interaction with the galaxy and will also address a serious challenge facing manned exploration by studying the region that shields us from the majority of galactic cosmic ray radiation"
Scientists call the edge of the Solar System the "termination shock" boundary because of the sudden drop in velocity of the solar wind - a blizzard of subatomic particles that stream out from the Sun - as it slows from supersonic to subsonic speeds.
The solar wind created by the Sun travels at a million miles per hour, creating a protective envelope around the entire Solar System that extends far beyond the most distant planets.
Ibex will capture images of the outer boundaries previously invisible to man.


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Posts: 131433
Date:
Pioneer Anomaly
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Title: On the gravitational origin of the Pioneer Anomaly
Authors: I. A. Siutsou, L. M. Tomilchik

From Doppler tracking data and data on circular motion of astronomical objects we obtain a metric of the Pioneer Anomaly. The metric resolves the issue of manifest absence of anomaly acceleration in orbits of the outer planets and extra-Pluto objects of the Solar system. However, it turns out that the energy-momentum tensor of matter, which generates such a gravitational field in GR, violates energy dominance conditions. At the same time the equation of state derived from the energy-momentum tensor is that of dark energy with w=-1/3. So the model proposed must be carefully studied by "Grand-Fit" investigations.

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Posts: 131433
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The pioneer anomaly
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The pioneer anomaly is a rather well established phenomena which is still lacking a satisfactory explanation.
The Spanish physicist Antonio F. Rañada, well known in his country by his textbook about classic dynamics, and also by a semi divulgative book of introduction to physics (I would add that his theory of topological treatment of electromagnetism, elaborated in collaboration with Jose Luis Trueba is very estimable) in collaboration with Alfredo Tiemblo have  written a paper that offers a possible explanation.

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