Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets

Understand

The Pioneer anomaly is a small sunward anomalous acceleration found in the trajectory analysis of the Pioneer 10 and 11 spacecraft.

• As part of the investigation of the effect, analysis of recently recovered Doppler data for both spacecraft has been completed.
• The presence of a small anomalous acceleration is confirmed using data spans more than twice as long as those that were previously analyzed.
• We examine the constancy and direction of the Pioneer anomaly, and conclude that: i) the data favor a temporally decaying anomalous acceleration (~2\times 10^{-11} m/s^2/yr) with an over 10% improvement in the residuals compared to a constant acceleration model; ii) although the direction of the acceleration remains imprecisely determined, we find no support in favor of a Sun-pointing direction over the Earth-pointing or along the spin-axis directions, and iii) support for an early "onset" of the acceleration remains weak in the pre-Saturn Pioneer 11 tracking data.