Simulation of Ambiguity Effects in Doppler Tracking of Pioneer Probes

Various models have been proposed to interpret the anomalous Pioneer Doppler data. We present in this paper a simulation tool aiming at determining signatures that could be searched in the data reduction process in order to discriminate between these different explanations. We discuss preliminary results on the seasonally modulated anomalies and compare two interpretations corresponding to a constant anomalous acceleration on one hand, to an anomalous curvature in the second sector of the gravity law on the other hand. Though the second sector interpretation could naturally induce large modulated anomalies, the adjustment of the initial conditions partly compensate these modulations and thus produces a signature resembling that of a constant acceleration. The difference between the predictions of the two interpretations is in fact close to the rms level of the residuals after the data analysis.     

Determination of the Equivalence Principle Violation Signal for the MICROSCOPE Space Mission: Optimization of the Signal Processing

The MICROSCOPE space mission aims at testing the Equivalence Principle (EP) with an accuracy of 10^?15. The test is based on the precise measurement delivered by a differential electrostatic accelerometer on-board a drag-free microsatellite which includes two cylindrical test masses submitted to the same gravitational field and made of different materials. The experiment consists in testing the equality of the electrostatic acceleration applied to the masses to maintain them relatively motionless at a well-known frequency. This high precision experiment is compatible with only very little perturbations. However, aliasing arises from the finite time span of the measurement, and is amplified by measurement losses. These effects perturb the measurement analysis. Numerical simulations have been run to estimate the contribution of a perturbation at any frequency on the EP violation frequency and to test its compatibility with the mission specifications. Moreover, different data analysis procedures have been considered to select the one minimizing these effects taking into account the uncertainty about the frequencies of the implicated signals.     

ODYSSEY, Orbit Determination Software for the Pioneer Data Analysis

The Pioneer anomaly refers to the difference between the computed trajectories of the Pioneer 10 and 11 spacecrafts and their actual trajectories as observed through Doppler tracking. This difference has been described by the Jet Propulsion Laboratory (JPL) as a constant anomalous acceleration. In order to perform an independent analysis, specific trajectography software, named ODYSSEY, has been developed. The paper will focus on the models implemented in this software and on the results obtained. The existence of a constant anomalous acceleration is confirmed with properties similar to those reported by JPL. Time dependent components of the anomaly are also found and discussed.