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Posted by baalke on October 18, 2007, 12:35 pm
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http://messenger.jhuapl.edu/news_room/status_report_10_17_07.html
MESSENGER Mission News
October 17, 2007
Critical Deep-Space Maneuver Targets MESSENGER for Its First Mercury
Encounter
The MESSENGER spacecraft delivered a critical deep-space maneuver on
Wednesday - 155 million miles (250 million kilometers) from Earth -
successfully firing its large bi-propellant engine to change the
probe's
trajectory and target it for its first flyby of Mercury on January 14,
2008.
"Completing this maneuver was a huge milestone for the mission,"
offered
MESSENGER Principal Investigator Sean Solomon. "We are now en route to
the closest glimpse of Mercury that anyone has ever seen. Over the
next
three months the suspense about what we will find will steadily
build."
The maneuver was executed in two parts from the MESSENGER Mission
Operations Center at the Johns Hopkins University Applied Physics
Laboratory (APL) in Laurel, Md. At 6 p.m. EDT on October 17, the probe
fired its large main engine for just over five minutes, using about 70
kilograms (154 pounds) of propellant to change its velocity by 226
meters per seconds, or just over 505 miles per hour.
Then, at 6:30 p.m. EDT, the small thrusters were fired for about two
minutes, changing the probe's velocity by an additional 1.4 meters per
second. This burn redistributed the propellant in the main tanks to
manage location of the probe's center of mass, putting the spacecraft
in
a more stable mode of operation. "This action lowers the risk of
having
to do momentum correction maneuvers during November, when interference
from the Sun will prevent communication with the spacecraft,"
explained
APL's Jim McAdams, who helped design this maneuver.
"Everything went as planned, and we are now on target for a flyby of
Mercury in January 2008," said Mission Operations Manager Andy
Calloway
of APL, adding that this maneuver was the most critical of the mission
other than orbit insertion, primarily because of the timing. "Deep-
Space
Maneuver-2 (DSM-2) was executed just nine days prior to the start of
the
longest solar conjunction communications outage period of the
mission,"
he said. "So there was limited opportunity to correct problems and to
obtain good orbit determination data for the navigation team."
"The MESSENGER team is breathing a lot easier now that we've seen the
successful completion of this most important course-correction
maneuver
before Mercury orbit insertion," McAdams said. "Not only did DSM-2 put
MESSENGER on target for the first spacecraft encounter with Mercury in
nearly 33 years, it was completed with the least margin for error of
all
five DSMs before Mercury arrival in March 2011."
This was the second 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. DSM-3 on
March
17, 2008, will position the probe for the second flyby of Mercury on
October 6, 2008. DSM-4 on December 6, 2008, positions MESSENGER for
Mercury flyby 3, scheduled for September 30, 2009. And the final
deep-space maneuver on November 29, 2009, targets the probe for
Mercury
orbit insertion on March 18, 2011.
"Now that we are past DSM-2, we will complete our solar conjunction
preparations and begin testing our final version of the Mercury
encounter sequence," Calloway said. "Once we exit the solar
conjunction,
we will finalize plans for the two December trajectory-correction
maneuvers - TCM-19 and TCM-20 - as we correct any propagated errors
from
DSM-2 so we can put MESSENGER right on the flyby aim point. It has
been
over three years of densely-packed cruise operations, and we are
finally
about to fly by and begin collecting data at Mercury."
------------------------------------------------------------------------
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.
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