January 12, 2008
The Calm before Close Approach
If you look at our "Where Is MESSENGER?" page, which displays the spacecraft's trajectory status, you'll see we're right on Mercury's doorstep. MESSENGER's mission design and navigation teams at the Applied Physics Laboratory (APL) in . , met yesterday to discuss the spacecraft's current trajectory to determine if a last-minute trajectory-correction maneuver would be needed.
The accumulated radiometric tracking data gathered since the last maneuver indicated that MESSENGER's current position is within 13 kilometers of the target aim point for the Mercury flyby, and direct optical measurements of the planet over the last four days are confirming this result. "The consistency of the radiometric and optical measurements of the trajectory ensure that the spacecraft is on target for the encounter," explained MESSENGER Mission Systems Engineer Eric Finnegan of APL. The bottom line? Trajectory-correction maneuver (TCM) 21, scheduled for execution on January 13, is not needed.
"Using these current predictions," Finnegan said, "the spacecraft will fly by the planet within 4 kilometers (2.5 miles) of the target altitude - Bull's Eye!" With just two days to the flyby, MESSENGER is on target to encounter Mercury at an altitude of 203 kilometers (126 miles) at approximately 19:04:39 UTC (2:04 p.m. EST).
"Operations has confirmed that the core Mercury command load sequence was on-board the spacecraft Thursday night, and all subsystems and instruments are operating nominally," Finnegan said. "On Friday night, the Gamma-Ray Spectrometer turned on its cooler in preparation for the flyby, and the Mercury Laser Altimeter was powered up this morning. The spacecraft is now fully configured for the encounter. All systems are 'GO' for flyby!"
The MESSENGER team will assemble in the operations center early Sunday morning to take one last look at the spacecraft before it starts to execute the core command sequence and turn its instrumentation toward Mercury for the first time in the mission. On to history …
View the Latest Optical Navigation Image of Mercury!
With just two days until MESSENGER's closest pass by Mercury, the Mercury Dual Imaging System is acquiring sets of images twice a day. These images are used for optical navigation, to verify that the spacecraft is on the desired course. The images also provide the first glimpse of Mercury by a spacecraft in more than 30 years, since the Mariner 10 mission in 1974 and 1975, and hint at the exciting images to come in the next week. This image was snapped on January 11, when MESSENGER was at a distance of about 1.7 million kilometers (1.1 million miles) from Mercury. The diameter of Mercury is about 4,880 kilometers (3,030 miles), and this image has a resolution of about 44 kilometers/pixel (27 miles/pixel).
As the spacecraft continues toward closest approach, additional information and features will be available online at http://messenger.jhuapl.edu/mer_flyby1.html, so check back frequently. Following the flyby, be sure to check back to see the latest released images and science results!
MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.