* Astronomy

MESSENGER Gains Gravity Assist for Mercury Orbital Observations
MESSENGER successfully flew by Mercury yesterday, gaining a critical gravity assist that will enable it to enter orbit about Mercury in 2011 and capturing images of five percent of the planet never before seen. With more than 90 percent of the planet's surface already imaged, MESSENGER's science team had drafted an ambitious observation campaign designed to tease out additional details from features uncovered during the first two flybys. But an unexpected signal loss prior to closest approach hampered those plans.

"This third and final flyby was MESSENGER's last opportunity to use the gravity of Mercury to meet the demands of the cruise trajectory without using the probe's limited supply of on-board propellant" - MESSENGER Mission Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

A portion of the complicated encounter was executed in eclipse, when the spacecraft is in Mercury's shadow and the spacecraft - absent solar power - was to operate on its internal batteries for 18 minutes. Ten minutes after entering eclipse and four minutes prior to the closet approach point, the carrier signal from the spacecraft was lost, earlier than expected.
According to Finnegan, the spacecraft autonomously transitioned to a safe operating mode, which pauses the execution of the command load and "safes the instruments," while maintaining knowledge of its operational state and preserving all data on the solid-state recorder.

"We believe this mode transition was initiated by the on-board fault management system due to an unexpected configuration of the power system during eclipse" - Eric Finnegan.

MESSENGER was returned to operational mode at 12:30 a.m. with all systems reporting nominal operations. All on-board stored data were returned to the ground by early morning and are being analysed to confirm the full sequence of events.

"Although the events did not transpire as planned, the primary purpose of the flyby, the gravity assist, appears to be completely successful. Furthermore, all approach observing sequences have been captured, filling in additional area of previously unexplored terrain and further exploring the exosphere of Mercury" - Eric Finnegan.

Source JHUAPL

Messenger spacecraft OK after brief shutdown
NASA's Messenger spacecraft is healthy after a brief shutdown during Tuesday's flyby of Mercury.
Four minutes before the closest approach at 5:55 p.m., while the spacecraft was flying on battery power in Mercury's shadow, signals were lost and on-board systems went into "safe" mode.

Source

A NASA spacecraft shut itself down shortly after beaming back images from a close approach of Mercury on Tuesday, its third and final flyby of the solar system's innermost planet before entering its orbit in 2011.
The Messenger probe went into "safe" mode, shutting down to prevent damage from an anomaly that engineers are now analysing.

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Signals from the spacecraft were lost about 6 p.m., just minutes after Messenger's closest approach. Educators sending tweets from the control center said the room grew quiet.
Source    

Radio signals received after the spacecraft emerged from behind the planet indicate that the spacecraft is operating nominally. Its instruments are now collecting images and other scientific measurements from the planet as it departs Mercury.
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Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

This image of Mercury was captured on the 29th September, 2009, by the Wide Angle Camera (WAC) aboard the Messenger spaceprobe, when it was  26,900 kilometres away from the planet.
The image shows never before seen terrain the sunlit side of the planet.
Image scale is 4.8 kilometres/pixel.