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Anomalous accelerations in spacecraft flybys of the Earth


The flyby anomaly is a persistent riddle in astrodynamics. Orbital analysis in several flybys of the Earth since the Galileo spacecraft flyby of the Earth in 1990 have shown that the asymptotic post-encounter velocity exhibits a difference with the initial velocity that cannot be attributed to conventional effects. To elucidate its origin, we have developed an orbital program for analyzing the trajectory of the spacecraft in the vicinity of the perigee, including both the Sun and the Moon’s tidal perturbations and the geopotential zonal, tesseral and sectorial harmonics provided by the EGM96 model. The magnitude and direction of the anomalous acceleration acting upon the spacecraft can be estimated from the orbital determination program by comparing with the trajectories fitted to telemetry data as provided by the mission teams. This acceleration amounts to a fraction of a \(\text{mm/s}^{2}\) and decays very fast with altitude. The possibility of some new physics of gravity in the altitude range for spacecraft flybys is discussed.

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  1. For recent overviews pointing to unsolved questions and perspectives see Iorio (2015a), Debono and Smoot (2016).

  2. For some recent critical discussions on its implications see Kennefick (2009), Longair (2015), Will (2015).

  3. For a comparative discussion of this measurement with other ones, see Iorio (2011c). Overviews of frame-dragging tests can be found in, e.g., Iorio et al. (2011), Renzetti (2013).


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I gratefully acknowledge NASA’s JPL for providing their orbital fits, for the missions considered in this paper, through the Horizon’s website.

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Correspondence to L. Acedo.

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Acedo, L. Anomalous accelerations in spacecraft flybys of the Earth. Astrophys Space Sci 362, 225 (2017).

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  • Flyby anomaly
  • Orbital model
  • Fifth force