Society for Popular Astronomy

A force to reckon with!
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Author:  Cliff [ Tue Oct 11, 2005 7:50 pm ]
Post subject:  A force to reckon with!

Dear al
One of the most intriguing mysteries in physics is the so-called Pioneer anomally, the slowing down of the two spacecraft Pioneers 10 and 11.
Both craft continued journeying at roughly 27,000mph but John Anderson of JPL has noticed anomalies in data going as far back as 1980. Both spacecraft seemed to be slowing down at a constant rate each year falling short about 8,000 miles of their supposed calculated positions.
The most obvious theories suggested something wrong with the crafts leaking gas, or heat radiation. But apparently that seems increasingly unlikely. Some physicists began to explore the possibility of flaws in Newton's laws and relativity. Others suggested Dark Matter. A third idea of a minute acceleration in the speed of light ie light was travelling faster than it might seem as if the probe was slowing down.
Nieto and Anderson suggest that the direction of the anomalies force works differently for each above theory.
If it points towards the Sun then it should be a gravitational effect. If it points towards Erth it should be an anomaly related to the velocity of light, but if in the direction of motion it should be a drag force or modification of inertia. Finally if it points along the spin axis it suggests a force along the spin axis of the probes, which could suggest a force generated by the space craft.
I understand one snag in doing analisis is that the further the spacecraft tavel out of the solar system then the angles between some of the above possible forces gets narrower and narrower and so tricky to establish results. So that is a reason why they are now going to check the early data of the space crafts travels again more closely.
Apparently depending on the nature of the Pioneer anomally it could possibly be related to MOND (modified newtonian dynamics).
At the moment it seems to be anyones guess what the outcome will be. Assuming there actually is one?
Best wishes from the Grumpy Old Codger Cliff

Author:  david entwistle [ Sat Apr 09, 2011 9:16 am ]
Post subject:  Re: A force to reckon with!

Cliff wrote:
At the moment it seems to be anyones guess what the outcome will be. Assuming there actually is one?

There's an article in April 8th 2011 Sky and Telescope with the title The "Pioneer Anomaly": Case Closed. It refers to a new paper: "Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft", by Francisco, Bertolami, Gil and 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.

Author:  Mogget [ Mon Apr 11, 2011 8:27 am ]
Post subject: 

I wonder if this theory can explain the slight difference between the computed acceleration of the Rosetta spacecraft during its Earth gravity assist manouevre, and the observed acceleration? If not, then we will have to start thinking about the Rosetta Anomaly :)

Author:  Cliff [ Mon May 16, 2011 3:08 pm ]
Post subject: 

Dear David and mogget
I only just noticed your new-ish comments related to the old post.
Thanks for the new gen and other thoughts.
Best wishes from Cliff

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