re: Acceleration directed towards the Sun. I thought that it was gravity.
From the above post:
"Our previous analyses of radio Doppler and ranging data from distant
spacecraft in the solar system indicated that an apparent anomalous
acceleration is acting on Pioneer 10 and 11, with a magnitude a_P ~ 8 x
10^{-8} cm/s^2, directed towards the Sun (anderson,moriond). Much effort has
been expended looking for possible systematic origins of the residuals, but
none has been found.
I have been under the impression that the solar system also has a gravity well somewhat similar to that of Earth.