Future satellite mission may help explain flyby anomaly

Technology Review : In 1990, NASA scientists detected an anomaly in the telemetry of the Galileo spacecraft while it was using Earth as a gravitational slingshot to help it on its way toward Jupiter. During the flyby, the craft’s speed suddenly increased 4 mm/s. A similar effect has been seen in three other flybys since. The anomaly only occurs when the observed trajectory of the spacecraft can’t be fit to a single hyperbolic arc. When the scientists have to use separate equations for the incoming and outgoing paths, there is a discrepancy that neither equation accounts for. But what causes the anomalous speed change is still uncertain. The European Space Agency is planning to launch a satellite in 2022 or 2024 that will have a highly eccentric orbit around Earth and may provide the opportunity to collect data that will help explain the slingshot anomaly.