Status Report: MESSENGER Team Prepares for December Maneuver
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 in space on December 12.
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 increase MESSENGER's speed relative to the Sun and set the arrival time for the first Venus flyby in October 2006. While the spacecraft's speed increases at the time of DSM 1, the spacecraft's average speed (over the course of a full orbit of the Sun) decreases after DSM 1.
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.
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.