The Quest
to Understand the Pioneer Anomaly
The Pioneer 10/11
missions, launched in 1972 and 1973, and their navigation are
reviewed. Beginning in about 1980 an unmodeled force of ~ 8 x
10^{-8} cm/s^2 appeared in the tracking data, it later being verified.
The cause remains unknown, although radiant heat remains a likely origin. A set
of efforts to find the solution are underway: a) analyzing in detail all
available data, b) using data from the New Horizons mission, and c)
considering an ESA dedicated mission.