MESSENGER Team Prepares for December Maneuver

http://messenger.jhuapl.edu/news_roo..._11_11_05.html

Status Report: MESSENGER Team Prepares for December Maneuver
MESSENGER Project
November 11, 2005

After successfully uploading new software to the MESSENGER spacecraft,
mission controllers at The Johns Hopkins University Applied Physics
Laboratory (APL) in Laurel, Maryland, are setting their sights on the
December Deep Space Maneuver (DSM-1), when the craft's large
bipropellant thruster will be fired for the first time.

The updated software was designed to address minor glitches in the
spacecraft guidance and control and command and data handling
subsystems. "The bugs were typical of those discovered post-launch,"
explains MESSENGER Mission Operations Manager Mark Holdridge of APL.
For
instance, shortly after launch they noticed that when the craft was in
the Earth acquisition mode, the lowest safe mode of operation, its
rotation gradually slowed down. That behavior was traced to a bug in
the
software, specifically to how the inertial measurement unit (IMU) data
were time tagged.

"You learn how to work around these things, but you'd rather fix them
in
the long-term," Holdridge says. He adds that "It's a little tricky to
load new software on a spacecraft while it's in flight and still
controlling the spacecraft's attitude. A couple of the fixes for
guidance and control should help improve the performance with the large
maneuver we have planned for December."

Following the software upload, the team conducted two tests to prepare
for that next milestone. One was to recalibrate the IMU. "We do this
type of periodical maintenance about every six months and before major
maneuvers," Holdridge explained. "Right now we are laying the
groundwork
so that the guidance and control folks can help prepare the command
loads for the upcoming maneuver."

DSM-1 will be the first of five such maneuvers planned for MESSENGER's
cruise, designed (with planetary flybys) to help the spacecraft reach
Mercury orbit. DSM-1 will reduce MESSENGER's speed relative to the Sun
and set the arrival time for the first Venus flyby in October 2006.

MESSENGER meets Venus!

On Nov. 7, 2005, the MESSENGER spacecraft passed inside the orbit of
Venus. While Venus was about 54 million miles from the spacecraft at
this time, the spacecraft was 67.2 million miles (108.1 million
kilometers) from the Sun. To keep tabs on MESSENGER's journey through
the inner solar system, use the "Where is MESSENGER?" feature on the
mission Web site - available at

http://messenger.jhuapl.edu/whereis/index.php

- which offers detailed, simulated views of the spacecraft's orbit;
MESSENGER's location in the solar system; and what Earth and Mercury
look like from MESSENGER's current perspective.

Stat Corner: MESSENGER is about 65.4 million miles (105.3 million
kilometers) from the Sun and 30.3 million miles (48.7 million
kilometers) from Earth. At that distance, a signal from Earth reaches
the spacecraft in 162.4 seconds. The spacecraft is moving around the
Sun
at 84,438 miles (135,890 kilometers) per hour. MESSENGER's onboard
computers have executed 113,780 commands from mission operators since
launch on Aug 3, 2004.