NASA's MESSENGER spacecraft, headed toward the first
study of Mercury from orbit, swung by its home planet on
Aug. 2 for a gravity assist that propelled it deeper into
the inner solar system.
Mission operators at the
Johns Hopkins Applied
Physics Laboratory say MESSENGER's systems performed
flawlessly as the spacecraft swooped around Earth, coming
to a closest approach point of about 1,458 miles over
central Mongolia at 3:13 p.m. EDT. The spacecraft used the
tug of Earth's gravity to change its trajectory
significantly, bringing its average orbit distance nearly
18 million miles closer to the sun and sending it toward
Venus for another gravity-assist flyby next year.
"One flyby down, five more to go," said APL's Mark
Holdridge, MESSENGER mission operations manager. "Now, the
mission begins."
Launched Aug. 3, 2004, from Cape Canaveral Air Force
Station, Fla., the solar-powered spacecraft is about 581
million miles into a 4.9-billion-mile voyage that includes
14 more loops around the sun. It will fly past Venus twice
and Mercury three times before moving into orbit around its
target planet. The Venus flybys in October 2006 and June
2007 will use the pull of the planet's gravity to guide
MESSENGER toward Mercury's orbit. The Mercury flybys in
January 2008, October 2008 and September 2009 help
MESSENGER further match that planet's speed, setting up the
maneuver in March 2011 that starts a yearlong science orbit
around Mercury.
"This Earth flyby is the first of a number of critical
mission milestones during MESSENGER's circuitous journey
toward Mercury orbit insertion," said Sean C. Solomon, the
mission's principal investigator, from the Carnegie
Institution of Washington. "Not only did it help the
spacecraft sharpen its aim toward our next maneuver, it
presented a special opportunity to calibrate several of our
science instruments."
MESSENGER's main camera had snapped several approach
shots of Earth and the moon over the past week, then began
taking a series of color images, beginning with South
America and continuing for one full Earth rotation, that
science team members will string into a "movie" documenting
MESSENGER's departure. On approach, the atmospheric and
surface composition spectrometer also made several scans of
the moon in conjunction with the camera observations, and
during the flyby, the particle and magnetic field
instruments spent several hours measuring Earth's
magnetosphere. The team will download the data and images
through NASA's Deep Space Network over the next several
weeks, continuing its assessment of the instruments'
performance.
MESSENGER will conduct the first orbital study of
Mercury, the least explored of the terrestrial ("rocky")
planets that also include Venus, Earth and Mars. Over one
Earth year — or four Mercury years — MESSENGER
will provide the first images of the entire planet and
collect detailed information on the composition and
structure of Mercury's crust, its geologic history, the
nature of its atmosphere and magnetosphere, and the makeup
of its core and polar materials.
MESSENGER, short for MErcury Surface, Space
ENvironment, GEochemistry and Ranging, is the seventh
mission in NASA's Discovery Program of lower cost,
scientifically focused exploration projects. APL designed,
built and operates the MESSENGER spacecraft and manages the
mission for NASA's Science Mission Directorate. For more
information, go to
messenger.jhuapl.edu.