On 23 January 1998, when NASA’s Near spacecraft swung past Earth on a routine flyby towards more interesting lands, a curious thing happened to its speed. It jumped by 13 mm/s.
This wasn’t the first time such an effect had been seen. Engineers saw similar jumps in speed during the Earth flybys of Galileo (in 1990 and 1992), Cassini (in 1999), Messenger (in 2005) and
Rosetta (also in 2005).
Various exotic explanations have been put forward but today it looks as if the explanation is far more prosaic. Jean Paul Mbelek from CEA-Saclay near Paris, France, says special relativity explains all.
The speed of the spacecraft is measured by the Doppler shift in radio signals from the craft. That makes the speed easy to calculate.
But Mbelek’s argument is that the relative motion of the spacecraft and the Earth (which is spinning) have not been properly accounted for. And when they are factored in, using special relativity, the flyby anomalies disappear.
Ref: arxiv.org/abs/0809.1888: Special Relativity May Account for the Spacecraft Flyby