Happy Anniversary, MESSENGER!
Today marks the third anniversary of MESSENGER's launch. Since its August 3, 2004, liftoff from Cape Canaveral Air Force Station, Fla., the probe has traveled nearly 1.9 billion miles on its circuitous journey from Earth to Mercury. "Anniversaries are important because they remind you of what it has taken to get you to this point," notes MESSENGER Project Scientist Dr. Ralph McNutt, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. "We have another successful year of operations under our belt, and everything is looking good. We are now heading into a period of activity that will include preparing for a record-breaking approach to the Sun, a major deep space maneuver on October 17, and a subsequent 48-day superior conjunction period [starting October 25], the longest of the mission."
First Perihelion Passage
The team will spend a good part of August preparing for the probe's first passage through perihelion, the closest point in its orbit around the Sun. On August 1, MESSENGER came within 0.5 astronomical units (AU) of the Sun, and by September 1 the probe will be within 0.33 AU to the Sun - that's 49.67 million kilometers (or 30.86 million miles) away, the closest any three-axis-stabilized spacecraft has ever approached the Sun. Mariner 10, the first spacecraft to explore Mercury, came within 0.47 AU.
To accommodate the extreme temperatures, the spacecraft has begun to tilt its solar arrays away from the Sun to balance the thermal limits of the array against the power generation needs of the spacecraft. "These solar array tilt adjustments will occur about every two to three weeks," explains APL's Sean Laughery, of MESSENGER's power engineering team. "Different values have been selected based on the spacecraft-to-Sun distance. For example, at 0.5 AU, the arrays were titled 50° back from their earlier position facing the Sun. When at 0.33 AU, the arrays will tilt 70° tilt past their Sun-normal position."
The team is also running tests to ensure that the spacecraft will operate as intended during MESSENGER's first flyby of Mercury on January 14, 2008. That flyby, along with two subsequent passes of Mercury on October 6, 2008, and September 29, 2009, will allow MESSENGER to image most of the hemisphere that Mariner 10 was not able to view (because it was in darkness during each of the three Mariner 10 flybys), and at higher resolution. MESSENGER will also map nearly the entire planet in color and measure the composition of the surface, atmosphere, and magnetosphere. These data will help the MESSENGER team plan the orbital mission, which begins on March 18, 2011.
"The MESSENGER mission will be nearly eight years in duration when all of the planned observations have been completed," says Dr. Sean C. Solomon, of the Carnegie Institution of Washington, who leads the mission as principal investigator. "At this three-year milestone, we have a healthy spacecraft and an experienced team with three planetary flybys successfully behind us. MESSENGER will be the first spacecraft to visit Mercury in more than 32 years, and our probe and our team are now ready to explore the innermost planet."
To view MESSENGER's current position, as well as its full orbital path since launch, go online to http://messenger/whereis/index.php.
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.