[mrsmith]

This is awful news.

Mystery force tugs distant probes
"By studying the Doppler shift (the "stretching") of the radio signals from the probe, scientists have been able to calculate how fast the craft is travelling. Since 1980, its trajectory has been mapped in very great detail.
The puzzle is that Pioneer 10 is slowing more quickly than it should. "

I thought this the most promising mystery in ages.
But without the signal there won't be any doppler-shift info on it's speed.

[axel f]

One night when I couldn't sleep I was listening to Art Bell, and he was talking about what you posted. Bell said that the force was pulling Pioneer 10 back toward Earth. Have you heard anything like that?