MESSENGER Eyes Its Target And Is Ready For Its Second Mercury Encounter
The MESSENGER spacecraft delivered a critical deep-space maneuver today ““ 64 million miles (103 million kilometers) from Earth ““ successfully firing its large bi-propellant engine to change the probe’s trajectory and target it for its second flyby of Mercury on October 6, 2008. This was the first trajectory-correction maneuver (TCM) to test the continuous slow rotation of the spacecraft throughout the burn, essential for the March 18, 2011, Mercury orbit-insertion (MOI) maneuver.
“Every propulsive event in this complex mission is an important step toward our ultimate goal ““ placing the first spacecraft into orbit about the innermost planet,” offers MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “Today’s deep-space maneuver is a crucial milestone that points us cleanly toward our next close look at Mercury in October.”
The 149-second maneuver began at 3:30 p.m. EDT. Mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel , Md. , verified the start of the maneuver about 5 minutes 42 seconds later, when the first signals indicating spacecraft thruster activity reached NASA’s Deep Space Network tracking station outside Goldstone, California.
The continuous rotation of the spacecraft occurred during the 90-second firing of the large bi-propellant engine, the main part of the 149-second TCM, and was less than 4Â° ““ about 11% of the turn required for the mission-critical MOI. The total change in velocity of 72.2 meters per second (161.5 miles per hour) achieved during the maneuver will increase the spacecraft’s speed relative to the Sun.
This was the third of five deep-space maneuvers that will help the spacecraft reach Mercury orbit. The first, on December 12, 2005, positioned the probe for its October 2006 flyby of Venus; the second, on October 17, 2007, targeted MESSENGER for its first flyby of Mercury this January.
DSM-4 on December 6, 2008, will position MESSENGER for Mercury flyby 3, scheduled for September 30, 2009. And the final deep-space maneuver on November 29, 2009, will target the probe for Mercury orbit insertion.
The next maneuver, TCM-24, is currently scheduled for April 24 and will be used to further fine-tune the trajectory for the second Mercury encounter. “There are also several instrument and subsystem calibrations this spring and summer, and even an instrument flight software load in July,” says MESSENGER Mission Operations Manager Andy Calloway of APL. “The MESSENGER team will also continue to focus on the Mercury Flyby 2 sequence planning and testing, as well as orbital operations planning in parallel with the ongoing flight operations.”
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