Information about the Pioneer Anomaly and anomalous velocity increases during Earth flyby's.

Chris P. Duif 



Space probes have exhibited unexplained changes in
speed during socalled Earth gravity assists
(see links on the left). When NASA's Galileo and NEAR spacecraft and ESA's Rosetta
flew
past Earth, they showed an expected change in speed. The
largest anomaly was recorded for NEAR, whose velocity changed 13
millimetres per second more than it should have. This excess is much
larger than the expected errors in measurement.
ESA Blog: Mystery remains: Rosetta fails to observe swingby anomaly
 P.G. Antreasian and J.R. Guinn, Investigations
into the unexpected deltaV increases during the Earth gravity assists
of Galileo and NEAR, AIAA 984287 (available at this site, pdf, 1.4
MB).
Abstract: Unexpected energy increases
during Earth flybys of both the Galileo and Near Earth Asteroid
Rendezvous (NEAR) spacecraft have drawn evidence of spacecraft
trajectory modeling errors, an unknown perturbing force or failure of
Newtonian gravity. This paper investigates the gravity field of Earth
as a possible source of these anomalous DeltaVs. Other possible
sources of errors are considered, including: the mathematical models
representing the perturbing forces acting on the spacecraft while in
the sphere of influence of Earth, such as relativistic effects, tidal
effects, Earth radiation pressure, and atmospheric drag. However, most
of these perturbations, such as atmospheric drag, can be ruled out
because the acceleration imparted to the spacecraft is several orders
of magnitude less than observed. Since the oblateness effect is several
orders of magnitude greater than the nongravitational perturbations,
errors in the spherical harmonic representation of Earth''s gravity
field are examined. Other sources that have already been examined and
tentatively dismissed include numerical roundoff, integration errors,
spacecraft antenna phase center offset, and spacecraft antenna
switching during encounter.
 J.D.
Anderson and J.G. Williams, Long range tests of the
equivalence principle, Class.
Quant. Grav. 18 (2001) 2447.
 Is the physics within the Solar system really
understood? C. Lämmerzahl, O. Preuss, H. Dittus. grqc/0604052.
 J.D. Anderson, J.K. Campbell, M.M. Nieto, The Energy Transfer Process in Planetary
Flybys, astroph/0608087.
 L. Iorio, The effect of general relativity on hyperbolic orbits and its application
to the flyby anomaly, grqc/0811.3924.

