MESSENGER's Third Gravity Assist Successful- next stop, Mercury Orbit!

By Emily Lakdawalla
September 30, 2009


MESSENGER captured this image of Mercury on approach to its third flyby, at about 19:47 on September 29, 2009. Credit: NASA / JHUAPL / CIW

Yesterday, the MESSENGER spacecraft sailed past Mercury at an altitude of just 228 kilometers (142 miles) and a relative speed of 5.4 kilometers per second (12,000 miles per hour). The close encounter provided MESSENGER with the "gravity assist" needed to slow the spacecraft enough that the next time it encounters Mercury, on March 8, 2011, it will be able to enter orbit. MESSENGER also gathered high-resolution images of half of the remaining 10 percent of the planet that had not before been photographed from spacecraft. "We are on course to Mercury orbit insertion less than 18 months from now, so we know that we will be returning to Mercury and will be able to observe the innermost planet in exquisite detail," project scientist Sean Solomon said in a statement to the press this morning.

However, just before closest approach, there was a glitch, and the spacecraft entered safe mode. The spacecraft is now back in normal operating mode and in good health, but the science observations planned for the departure phase of the flyby were missed.

The encounter called for MESSENGER to fly over Mercury's night side, with a crescent phase of the planet visible to the spacecraft on approach. Fourteen minutes before closest approach, the spacecraft passed into Mercury's shadow, so needed to switch from solar power to its batteries. Ten minutes after entering the shadow and four minutes before closest approach, mission controllers on the ground unexpectedly lost MESSENGER's radio signal. At eight minutes after closest approach, the spacecraft passed behind Mercury as seen from Earth, resulting in an expected loss of signal for another 52 minutes. During that radio blackout, mission controllers worked feverishly to understand the unexplained loss of MESSENGER's signal, and waited on tenterhooks to hear MESSENGER's signal again as it emerged from behind Mercury.

Engineers now know that the loss of signal occurred when the spacecraft autonomously entered "safe mode," a condition in which the spacecraft ceases non-essential operations and turns to Earth to wait for instructions. "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,” said MESSENGER mission systems engineer Eric Finnegan. The press statement goes on to say that "MESSENGER was returned to operational mode at 12:30 a.m. with all systems reporting nominal operations. All on-board stored data were retuned to the ground by early morning and are being analyzed to confirm the full sequence of events."

more:

http://planetary.org/news/2009/0930_MESSENGERs_Third_Gravity_Assist.html

Tell him there's oil there AND prisoners to be tortured and you won't be able to stop him.