5 The Original 1995 – 2002 Study of the Pioneer Anomaly

The Pioneer 10 and 11 spacecraft have been described informally as the most precisely navigated deep space vehicles to date. Such precise navigation [24Jump To The Next Citation Point27Jump To The Next Citation Point260262390Jump To The Next Citation Point391Jump To The Next Citation Point392Jump To The Next Citation Point393Jump To The Next Citation Point] was made possible by many factors, including a conservative design (see Figure 2.3View Image for a design drawing of the spacecraft) that placed the spacecraft’s RTGs at the end of extended booms, providing added stability and reducing thermal effects. For attitude control, the spacecraft were spin-stabilized, requiring a minimum number of attitude correction maneuvers, further reducing navigation noise. As a result, precision navigation of the Pioneer spacecraft was possible across multi-year stretches spanning a decade or more [269].

Due in part to these excellent navigational capabilities, NASA supported a proposal to extend the Pioneer 10 and 11 missions beyond the originally planned mission durations, and use the spacecraft in an attempt to perform deep space celestial mechanics experiments, as proposed by J.D. Anderson from the Jet Propulsion Laboratory (JPL). Starting in 1979, the team led by Anderson began a systematic search for unmodeled accelerations in the trajectories of the two spacecraft. The principal aim of this investigation was the search for a hypothetical tenth planet, Planet X. Later, Pioneer 10 and 11 were used to search for trans-Neptunian objects; the superior quality of their Doppler tracking results also yielded the first ever limits on low frequency gravitational radiation [27Jump To The Next Citation Point].

The acceleration sensitivity of the Pioneer 10 and 11 spacecraft was at the level of ∼ 10–10 m/s2. At this level of sensitivity, however, a small, anomalous, apparently constant Doppler frequency drift was detected [24Jump To The Next Citation Point27Jump To The Next Citation Point390Jump To The Next Citation Point].

 5.1 The early evidence for the anomaly and the original study
 5.2 The 2002 formal solution for the anomalous acceleration
 5.3 Sources of systematic error external to the spacecraft
  5.3.1 Direct solar radiation pressure and mass
  5.3.2 The solar wind
  5.3.3 The effects of the solar corona
  5.3.4 Electro-magnetic Lorentz forces
  5.3.5 The Kuiper belt’s gravity
  5.3.6 Stability of the frequency references
  5.3.7 Stability of DSN antenna complexes
 5.4 Sources of systematic error internal to the spacecraft
  5.4.1 Propulsive mass expulsion
  5.4.2 Heat from the RTGs
  5.4.3 Nonisotropic radiative cooling of the spacecraft
  5.4.4 Radio beam reaction force
  5.4.5 Expelled helium produced within the RTGs
  5.4.6 Variation between determinations from the two spacecraft
 5.5 Computational systematics
  5.5.1 Numerical stability of least-squares estimation
  5.5.2 Model consistency
  5.5.3 Error due to mismodeling of maneuvers
  5.5.4 Annual/diurnal mismodeling uncertainty
 5.6 Error budget and the final 2002 result

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