Hope for astronomers stumped
by 'flyby anomoly'
23 November 2013
A mystery that has stumped scientists for decades might be one step
closer to solution after ESA tracking stations carefully recorded
signals from the Juno spacecraft as it swung by Earth
NASA's deep-space probe zipped past to within 561 km as it picked up
a gravitational speed boost to help it reach Jupiter in 2016. During the
high-speed event, radio signals from Juno were carefully recorded by ESA
tracking stations in Argentina and Australia. Engineers hope that the
new measurements will unravel the decades-old 'flyby anomaly' — an
unexplained variation in spacecraft speeds detected during some swingbys.
"We detected the flyby anomaly during Rosetta's first Earth visit in
March 2005," says Trevor Morley, flight dynamics expert at the
operations centre in Darmstadt, Germany. "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."
Since 1990, mission controllers at ESA and NASA have noticed that
their spacecraft sometimes experience a strange variation in the amount
of orbital energy they pick up from Earth during flybys, a technique
routinely used to fling satellites deep into our Solar System. The
unexplained variation is noticed as a tiny difference in the expected
speed gained (or lost) during the passage.
The variations are extremely small: NASA's Jupiter probe ended up
just 3.9 mm/s faster than expected when it swung past Earth in December
1990. The largest variation — a boost of 13.0 mm/s — was seen with
NASA's NEAR asteroid craft in January 1998. Conversely, the differences
during swingbys of NASA's Cassini in 1999 and Messenger in 2005 were so
small that they could not be confirmed. The experts are stumped.
NASA's Juno spacecraft approaching Earth on 9
October 2013 (artist's rendering). NASA's deep-space probe zipped past
to within 561 km of Earth. (Credit: NASA)
Engineers and the flight dynamics teams watched closely as the new 35
m deep-space dish in Malargüe, Argentina, and a smaller 15 m dish in
Perth, Australia, tracked Juno. The stations recorded highly precise
radio-signal information that will indicate whether Juno speeded up or
slowed down more or less than predicted by current theories. The results
are being studied closely by ESA and NASA as well as scientists
worldwide, who are hoping to see whether the anomaly has again detected.
"Our Malargüe station is designed to track very distant and
relatively slow-moving spacecraft, while Juno will pass by moving very,
very fast at just 561 km altitude," said ESA's Daniel Firre, responsible
for the tracking support at ESOC. "This makes tracking Juno technically
very challenging, but it's how the scientific process works. Gathering
more data that can be analysed by experts is critical if we are ever to
solve this perplexing mystery."