The flyby anomaly is an unexpected energy increase during Earth-flybys In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save fuel, time, and expense. Gravity assist can be used to decelerate or accelerate a of spacecraft. This anomaly has been observed as a shift in the S-Band The S band ranges from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part of the microwave band of the electromagnetic spectrum. The S band is used by weather radar, surface ship radar, and some communications satellites, especially those used by NASA to communicate with the Space Shuttle and the and X-Band The X-band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X-band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified by the IEEE at 8.0 to 12.0 GHz Doppler The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to and the ranging data. Taken together it causes a significant unaccounted velocity increase of over 13 mm/s during flybys[1]
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