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The '''Pioneer anomaly''' refers to deviations in projected courses for several spacecraft sent to the outer solar system.  The effect is believed to have influenced the courses of both Pioneer spacecraft, Galileo, and Ulysses.  The courses for the Voyager spacecraft and Cassini were not able to be predicted accurately due to known but unpredictable effects on these craft, and if the anomaly affects these spacecraft, it would not be distinguishable from other effects.

The '''Pioneer anomaly''' refers to deviations in projected courses for several spacecraft sent to the outer solar system.  The effect is believed to have influenced the courses of both Pioneer spacecraft, Galileo, and Ulysses.  The courses for the Voyager spacecraft and Cassini were not able to be predicted accurately due to known but unpredictable effects on these craft, and if the anomaly affects these spacecraft, it would not be distinguishable from other effects.

Critics of [[General relativity|general relativity]] cite the Pioneer anomaly as evidence that the theory is in error.

The Pioneer anomaly may be evidence that our understanding of gravity (Newtonian mechanics and [[General relativity|general relativity]]) needs to be improved.

==Discovery==

==Discovery==

* The anomalous acceleration could be due to the spacecraft venting energy in certain directions.<ref>http://www.symmetrymagazine.org/breaking/2008/04/13/pioneer-spacecraft-a-step-closer-to-being-boring/</ref>.  However, such effects would be expected to be more significant earlier on, when the power sources were less degraded<ref name="Nieto" />.  The opposite was actually the case.

* The anomalous acceleration could be due to the spacecraft venting energy in certain directions.<ref>http://www.symmetrymagazine.org/breaking/2008/04/13/pioneer-spacecraft-a-step-closer-to-being-boring/</ref>.  However, such effects would be expected to be more significant earlier on, when the power sources were less degraded<ref name="Nieto" />.  The opposite was actually the case.

* The theory of [[General Relativity]] and the [[Law of Universal Gravitation]] could be wrong; the gravitational force could be slightly stronger than predicted.  In this context, it is important to note that other spacecraft flying in hyperbolic trajectories around celestial bodies have also experienced anomalous gravitational effects.

* The theory of [[General Relativity]] and the [[Law of Universal Gravitation]] could be wrong; the gravitational force could be slightly stronger than predicted.  In this context, it is important to note that other spacecraft flying in hyperbolic trajectories around celestial bodies have also experienced anomalous gravitational effects.

* There could be gravitational forces from other celestial bodies that have not been taken into account.  Dr. [[Russell Humphreys]] has explained<ref name="Humphreys">Russell Humphreys.  "[http://creation.com/images/journal_of_creation/vol21/5181creationist.pdf Creationist cosmologies explain the anomalous acceleration of Pioneer spacecraft]."  ''Journal of Creation'', August 2007.</ref> the Pioneer Anomaly as part of [[Starlight_problem#Humphreys.27_model|his new cosmology]], as the pull from the center of mass of the universe.  This would prove that the universe exists in only three dimensions, not four, as the [[Big Bang]] theory predicts.

* There could be gravitational forces from other celestial bodies that have not been taken into account.  Dr. [[Russell Humphreys]] has explained<ref name="Humphreys">Russell Humphreys.  "[http://creation.com/images/journal_of_creation/vol21/5181creationist.pdf Creationist cosmologies explain the anomalous acceleration of Pioneer spacecraft]."  ''Journal of Creation'', August 2007.</ref> the Pioneer Anomaly as part of [[Starlight_problem#Humphreys.27_model|his new cosmology]], as the pull from the center of mass of the universe.  However, since the two spacecraft are going in opposite directions, an attraction or potential well from the "center of the universe" can't explain it.  In any case, such an attraction would act on the entire Solar system, so its effects would cancel.

 

==References==

==References==

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