# The Anomalous Acceleration of the Pioneer Spacecrafts

1. Jul 4, 2008

### Garth

A nice review of the anomaly has just been published on the Physics ArXiv as a result of an "Invited talk in Astronomia Dinamica en Latinoamerica. To be published in Revista Mexicana de Astronomia y Astrofisica, Conference Series."

The Anomalous Acceleration of the Pioneer Spacecrafts with the PDF document here.

Given the necessity and unverified nature of DM and DE in the standard $\Lambda$CDM cosmological model, I would have thought a dedicated mission to explore the PA ought to have the highest priority. It seems our standard theory of gravitation is incomplete in some way.

Garth

2. Jul 4, 2008

### robheus

Was't this pioneer anomaly attributed simply to the fact that the region of space (near the Kuiper belt) contains dust, and that the anomolous force (directed towards the sun) thus is an indirect experiment which shows the density of matter in that region?

Also I saw reports which attributed this anomaly to the pioneer instruments themselves causing an a-symetric force on the spaceship (leaking gas or heat effects or something).

3. Jul 4, 2008

### Garth

Hi robheus, yes there are many suggestions as to the cause of the PA; read the paper, it explores them all.

Garth

4. Jul 4, 2008

### paw

Well it is an interesting read Garth but there's a lot of reliance on the anomaly being constant. Many of the potential causes are dismissed for this reason. But the data, according to Olsen, "is not accurate enough to distinguish between a constant acceleration and acceleration proportional to the remaining plutonium in the RTG's". That kind of blows most of the paper out of the water as far as I'm concerned.

They dismiss the possibility of computation error because the anomaly is present in independant studies using different software. However, using different software doesn't guarantee a different algorithm. And further, different software may still be subject to the same hardware constraints. Math co-processers operate using the same rounding and truncating standards and the sig figs from hardware rounding are of the same order of magnitude as the anomaly. I'd almost bet that's where the anomoly really comes from.

5. Jul 4, 2008

### Garth

The data is not accurate enough, which is why a dedicated mission is advocated, however it is consistent to within the accuracy of observation.

The 'constancy' of the effect is relative to a 1/r{sup]2[/sup] or 1/r dependence that might be easier to explain or inded relative to a very locally varying effect that might be caused by a 'Planet X', the original reason for the data analysis.

True plutonium radioactive decay is also nearly constant over these timescale but any asymmetric radiation could account for only about an order of magnitude less than the observed effect, with other explanations using 'normal physics' from On-Board Systematics, (source The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation Turyshev et al.), they can so far explain a maximum of:

i Radio Beam Reaction Forc arb = (1.10 ± 0.10) × 10−10 m/s2. .
ii Anisotropic Heat Reflection aah = (−0.55 ± 0.55) × 10−10 m/s2. .
iii Differential Change of the RTG’s Radiant Emissivity are = 0.85 × 10−10 m/s2. .
iv Constant Electrical Heat Radiation as the Source: not viable.
v Helium Expulsion from the RTGs ahe = (0.15 ± 0.16) × 10−10 m/s2. .
vi Propulsive Mass Expulsion apme = ±0.56 × 10−10 m/s2.

This makes a maximum total of an = (2.1 ± 0.8) × 10−10 m/s2 that can be caused by normal physics leaving at least a minimum anomalous acceleration of ax = (6.6 ± 2.1) × 10−10 m/s2 to be explained.

I agree the data needs to be more accurate, nevertheless with the present data is inconsistent with GR with the present error bars on the various possible causes.

Garth

6. Sep 17, 2008

### Garth

Pioneer Doppler data analysis: study of periodic anomalies submitted on today's physics ArXiv by Prof. Dr. Reynaud of the Laboratoire Kastler Brossel, Université Pierre et Matie Curie, Paris.
Garth

7. Nov 9, 2008

### tony873004

Jon Giorgini of JPL Horizons was asked about the Pioneer Anomaly during the Q&A following his acceptance speech for the Masursky Award. He said:

"It's been studied fairly intensively. The conclusion is that it's very well described by the thermal radiation model. Discrepancies or inadequacies in the model of how heat is radiated off of it explains this anomalous acceleration. If you correct the heat model you can reduce this mysterious effect, so it doesn't represent new physics. It appears to represent mis modeling of thermal radiation."

You can view his speech here:
Skip forward to 1:30:10 for the Pioneer Anomaly question.

Last edited by a moderator: May 3, 2017
8. Nov 11, 2008

### Enthalpy

Hello everybody!

I'd like to recommend to everybody to read at least the chapter titles of the original paper by Anderson, Turyshev and many others. Available for free on ArXiv. They really analysed many possible causes and ruled them out. This does include dust, additional planets, radiation pressure from the radioisotopic generator and the Sun, Solar wind, relativistic corrections and many many more.

This should avoid to suggest explanations that are already ruled out.

9. Nov 11, 2008

### Enthalpy

As for the heat radiation:

- I believe Turysha and others more than Giorgini, for they made the analysis (page 34), not he. Any publication by Turysha saying that?

- Worse: you can easily compute by yourself what the maximum radiation force is. It's 39nm/s2 if fully asymmetrical, or about 50 times the anomaly. Even if the craft wasn't modelled that precisely before flight, any rough estimation is better than 2% anisotropy. Remember this is heat radiation at the tip of a boom.

10. Nov 11, 2008

### Enthalpy

Software:

Yes, two teams contracted by Anderson et al used really different softwares based on different algorithms - that is, different libraries, but same physics. Already checked in the initial paper.

This will rule out rounding errors as well: they won't add up identically in two different programs.