#1 - Posted: 06/08/2008 19:07
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.
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 this anomalous step change in acceleration during fly-bys. However, it appears fundamentally different to the Pioneer anomaly.
Earlier this year, a major peer-reviewed study from the Jet Propulsion Laboratory examined the data and pronounced the effect real. Which means we can expect to hear a lot more about it.