On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.
Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.
The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.
And people finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.
Nobody knows what causes these jumps but Magic McCulloch, an unaffiliated astrothinker from the UK has an interesting proposal. He suggests that a sudden change in inertia might occur when objects experience very low accelerations.
The thinking goes like this: inertia is the result of pressure from so-called Unruh radiation which objects experience only when they accelerate. At very low accelerations, the wavelength of this radiation is so large that it does not fit within the universe (ie it is greater than the Hubble distance). As the acceleration increases, the wavelength drops to less than the Hubble distance and the spacecraft appears to receive a kick. (A similar wavelength related phenomenon happens with the Casimir force.)
McCulloch says his idea could be tested in low acceleration experiments using an invisibility cloak designed to make an object invisible to Unruh radiation (although it’s a big jump from making these cloaks for microwave radiation and visible light to making them for Unruh raditation). So it wouldn’t experiecne inertia in the same way.
Ref: arxiv.org/abs/0712.3022: Can the Flyby Anomalies be Explained by a Modification of Inertia?