I found this Mercury announcement exciting.
One Year until Mercury Orbit Insertion
We are finally closing in on the most intense phase of the mission, says
MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution
of Washington. MESSENGERs six and a half years of interplanetary flight
are a long warm-up for the main event, when we are in orbit about Mercury.
The final year of that flight will be a busy time for the team, as we
review orbital operation plans for all spacecraft subsystems.
Entering orbit about Mercury will require the probe to perform the largest
propulsive maneuver of the entire mission. For Mercury orbit insertion
(MOI), MESSENGER will point its largest thruster very close to the
direction of travel and fire that thruster for nearly 14 minutes as well
as other thrusters for an additional minute, slowing the spacecraft by 862
meters per second (1,929 miles per hour) and consuming 31% of the
propellant that the spacecraft carried at launch.
For an animation of the orbit insertion maneuver and initial orbit of
Mercury, see http://messenger.jhuapl.edu/the_mission/gallery.html. Two
animations and various view perspectives of the orbit insertion maneuver
and initial orbit of Mercury are available at
Less than 9.5% of the usable propellant at the start of the mission will
remain after completing the orbit insertion maneuver, but the spacecraft
will still have plenty of propellant for future orbit correction
maneuvers, says MESSENGER Mission Design Engineer Jim McAdams of the
Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.
MESSENGER engineers recently tweaked the strategy for entering into orbit
about Mercury. MESSENGERs propulsion system has consistently performed
with high accuracy, McAdams explains. We replaced an MOI clean-up
maneuver with a placeholder for a contingency clean-up maneuver, which
reduces risk by simplifying the orbit insertion process.
Another change affecting the orbit insertion is a shift in the spacecraft
orbits tilt relative to Mercurys equator plane, from 80.0° to 82.5°, a
carefully studied change that will improve overall science data returned
during the Mercury orbital phase, McAdams says.
The orbit insertion will place the spacecraft into an initial orbit about
Mercury that has a 200 kilometer (124 mile) minimum altitude and a period
of 12 hours. At the time of orbit insertion, MESSENGER will be 46.14
million kilometers (28.67 million miles) from the Sun and 155.06 million
kilometers (96.35 million miles) from Earth.