Different dedicated and non-dedicated missions to test the anomalous accelaration of the Pioneer spacecraft have been investigated.
In this project two plausible mission architectures for the exploration of the outer solar system have been considered that may also be used to test the Pioneer anomaly. First, a class of low-mass low-thrust missions to Pluto, Neptune, or Uranus. For this mission type, the Pioneer anomaly investigation can be performed by radio tracking of the exploration spacecraft. The other mission paradigm considered is that of a microspacecraft piggybacked on a large nuclear-reactorpowered spacecraft sent to explore Jupiter or Saturn. The small spacecraftwould be jettisoned from the mothercraft on the approach to its destination, would use the target planet of the mothercraft for a powered swingby, and subsequently performs the Pioneer anomaly investigation by radio tracking on a hyperbolic coast arc. For both mission types minimal requirements for the spacecraft design and trajectory have been derived.
For both mission paradigms, the detection of the anomaly is found to be possible during the whole measurement phase, which extends over several years. Onboard systematics would still limit the precision in the determination of the magnitude of the anomaly to approximately 10%. This does not seem much of an improvement compared to the 15% error margin of the original determination from Pioneer 10 and 11 tracking data. However, by using suitable system design solutions, a nondedicated test would be able to rule out the last candidate onboard sources of the anomaly. Furthermore, the simple requirement of a minimal flight angle for the trajectories enables the discrimination between the most plausible classes of candidate models for the anomaly. The attainable acceleration sensitivity of about 8Ã-10 â^'11 m/s2 will be insufficient for a precise characterization of the anomaly. In particular, a slope of the anomaly would most likely only be determined to the first order, if at all. This would hardly be sufficient to determine unambiguously the physical law that might underlie the Pioneer anomaly. Hence, the quality of the scientific return of nondedicated missions cannot compete with a dedicated mission for which acceleration sensitivities down to 10â^'12 m/s2 would be attainable. In view of the ongoing controversial discussion about the origin of the Pioneer anomaly and the extraordinary costs of a dedicated deep-space mission to the outer solar system, however, it seems more appropriate to consider the more modest approach of using a nondedicated mission to verify if the Pioneer anomaly is indeed an indication of a novel physical effect.