Pioneer Anomaly Solved By 1970s Computer Graphics 169
Frans Faase updated us on a Pioneer Mystery we've been following for many years: something is tugging Pioneer 10 & 11. A few years ago a theory surfaced but now "A new computer model of the way heat is emitted by various parts of the Pioneer spacecraft, and reflected off others, finally solves one of the biggest mysteries in astrophysics. Previous calculations have only estimated the effect of reflections. A computer modeling technique called Phong shading was used to work out exactly how the the emitted heat is reflected (PDF) and in which direction it ends up traveling. Taking into account the reflections on the antenna seem to make the anomaly disappear."
But... Phong is wrong (Score:4, Interesting)
Re:To be fair... (Score:5, Interesting)
Re:But... Phong is wrong (Score:4, Interesting)
The main problem with Phong is, that it can create energy depending on the parameters. Meaning the emitted light can be stronger than the incident light and so in that calculation create thrust out of nowhere.
Additionally the Pioneer probes are made out of metal, Phong is derived from a model of plastic. The properties of those two materials are quite different, one being a conductor the other an insulator, so the Fresnel equation gives quite different values for the reflective properties, additionally metals are often anisotropic in their reflection capabilities. This has influence on the direction and form of the lobe for the first order effects. I also don't understand, why they didn't use one of the established BRDFs which are at least physically correct.
I looked through the paper and I see no prove, that the parameters they assume for diffuse and specular reflection don't violate the laws of physics.