A MISSION TO EXPLORE THE PIONEER ANOMALY

AbstractThe Pioneer 10 and 11 spacecraft yielded the mostprecise navigation in deep space to date. These spacecrafthad exceptional acceleration sensitivity. However, analysisof their radio-metric tracking data has consistently indi-cated that at heliocentric distances of ∼20–70 astronomi-cal units, the orbit determinations indicated the presenceof asmall, anomalous,Dopplerfrequency drift. The drift isa blue-shift, uniformly changing with a rate of ∼ (5.99 ±0.01) × 10 −9 Hz/s, which can be interpreted as a con-stant sunward acceleration of each particular spacecraftof a P = (8.74±1.33)×10 −10 m/s 2 (Anderson et al. 1998;Turyshev et al. 1999; Anderson et al. 2002a). The natureof this anomaly remains unexplained. This signal has be-come known as the Pioneer anomaly.The inability to explain the anomalous behavior ofthe Pioneers with conventional physics has contributedto growing discussion about its origin. There is now anincreasing number of proposals that attempt to explainthe anomaly outside conventional physics. This progressemphasizes the need for a new experiment to explore thedetected signal. Furthermore, the recent extensive effortsled to the conclusion that only a dedicated experimentcould ultimately determine the nature of the found signal.We discuss the Pioneer anomaly and present the nextsteps towards an understanding of its origin. We specifi-cally focus on the development of a mission to explore thePioneer Anomaly in a dedicated experiment conducted indeep space. This joint European-US mission is motivatedby the desire to better understand the laws of fundamen-tal physics as they affect dynamics in the solar system.The mission could lead to a major discovery in the 21stcentury and, with readily available technologies, it couldbe flown well within the Cosmic Vision time frame.Key words: Fundamental physics, Pioneer anomaly, solarsystem dynamics, deep space navigation, gravitation1. BackgroundThe exploration of the solar system’s frontiers - the regionbetween 25-250 astronomical units (AU) from the Sun -is a most ambitious and exciting technological challenge.The scientific goals for possible deep-space missions arewell-recognized and include studies of the gas and dustdistributions, exploration of the heliopause and the spacebeyond, measurements of the magnetic fields and particlefluxes, studies of the Oort Cloud and Kuiper Belt Objects,encounters with distant bodies, and investigation of thedynamical background of the solar system by studying