NASA’s Juno spacecraft is scheduled to fly close to the Earth today, coming within 350 miles of Earth and swinging around it. The probe will be accelerated on to Jupiter, where it will begin research in 2016.

The event is a common one for spacecraft, which commonly use the gravity of celestial bodies to accelerate. This particular event, however, is of particular importance to engineers, as it could help the determine why their calculations of such events are sometimes off the mark. Tracking stations in the southern hemisphere will be recording radio signals from the spacecraft as it accelerates past the planet. If Juno’s post-flyby velocity doesn’t match what researchers have predicted, the radio data could be important for determining why that is the case.

For over two decades, researchers have found discrepancies between the measured outcome and their predictions of how much energy spacecraft will acquire after a flyby of Earth. The discrepancies aren’t large, with the largest being NASA’s NEAR spacecraft, which ended up with a speed 13 mm per second faster than that predicted by the math. They also don’t occur during every flyby, making it difficult to track down just what may be causing the error.

“We detected the flyby anomaly during Rosetta’s first Earth visit in March 2005,” said Trevor Morley, a flight dynamics expert at European Space Agency’s (ESA) ESOC operations centre. Morley refers to the Rosetta spacecraft, launched in 2004 on a mission to study comets. ESA dishes in Argentina and Australia will be used to gather the radio data from Juno.

“Frustratingly, no anomaly was seen during Rosetta’s subsequent Earth flybys in 2007 and 2011. This is a real cosmic mystery that no one has yet figured out.”

(Image courtesy NASA)