MESSENGER Engine Burn Puts Spacecraft on Track for Venus

http://messenger.jhuapl.edu/news_roo..._12_12_05.html

MESSENGER Engine Burn Puts Spacecraft on Track for Venus
December 12, 2005

At 6:30 a.m. (EST) today NASA's Mercury-bound MESSENGER spacecraft
successfully fired its large bipropellant thruster for the first time
since launch, completing the first of several critical deep space
maneuvers that will help the spacecraft reach Mercury orbit.

The 524-second burn changed MESSENGER's velocity by about 316 meters
per
second (706 miles per hour), putting the solar-powered spacecraft on
track for a 3,140-kilometer (1,951-mile) altitude flyby of Venus on
October 24, 2006.

"This is a major accomplishment for the mission," said MESSENGER
Mission
Operations Manager Mark Holdridge, of the Johns Hopkins University
Applied Physics Laboratory (APL), Laurel, Md. "That bi-prop engine is
the last major component of the spacecraft that we haven't used in
space
and one we'll need at least five more times to orbit Mercury. The
successful performance of this main engine proves that the spacecraft
is
up to the task."

Until today, only 16 of the MESSENGER spacecraft's 17 thrusters had
been
used in five small trajectory correction maneuvers. This latest
maneuver, known as Deep Space Maneuver 1 (DSM 1), is the first to rely
solely on the largest, most efficient thruster.

"Maneuvers performed with the largest thruster use about 30% less
propellant, including both fuel and oxidizer, than the other thrusters,
which use fuel only," explained APL's Jim McAdams, the mission design
team leader. "About 18 percent of MESSENGER's propellant was used to
complete DSM 1. Of all planned course-correction maneuvers for
MESSENGER, DSM 1 is second only to the March 18, 2011, Mercury orbit
insertion maneuver in velocity change."

MESSENGER controllers monitored the engine burn from the Mission
Operations Center at APL. This change in the spacecraft's speed is
about
equal to the speed of a jet as it reaches the sound barrier.

"Credit for the completion of this important milestone belongs to the
entire MESSENGER team," noted Dave Grant, MESSENGER program manager at
APL. "We are very fortunate to have a highly skilled group of
engineers,
scientists and operations experts leading our journey to Mercury. Their
untiring diligence in preparing for this maneuver has been rewarded
with
a great success."

Looking Forward

For the next 10 months, mission controllers at APL will perform routine
housekeeping tasks and fine-tune instruments to prepare MESSENGER for
the Venus flyby, the first of two Venus flybys that will use the pull
of
the planet's gravity to guide MESSENGER toward Mercury's orbit. This
maneuver will occur near the beginning of an approximately two-week
period when the apparent spacecraft position is too close to the Sun to
allow communications with the spacecraft. So the team will spend the
next several months getting the spacecraft ready to fly safely for an
extended period of time without ground contact.

During a 7.9-billion kilometer (4.9-billion mile) journey that includes
15 trips around the Sun, MESSENGER will fly past Venus twice and
Mercury
three times before easing into orbit around its target planet. As with
the October 2006 event, the second Venus flyby in June 2007 will be a
gravity-assist maneuver. The Mercury flybys in January 2008, October
2008 and September 2009 will help MESSENGER match the planet's speed
and
location for an orbit insertion maneuver in March 2011 that starts the
first-ever study of Mercury from orbit.

With just over 20% of the flight time completed between launch and
Mercury orbit insertion, MESSENGER has traveled more than 1.3 billion
kilometers (0.81 billion miles) around the Sun. Since its August 2004
launch, the spacecraft has completed 1.5 orbits of the Sun, including a
successful flyby of Earth in August 2005. Follow the spacecraft on its
path to Mercury on the "Where Is MESSENGER?" Web site,
http://messenger.jhuapl.edu/whereis/index.php.

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. Dr. Sean C. Solomon,
of the Carnegie Institution of Washington, leads the mission as
principal investigator. APL manages the mission for NASA, built
MESSENGER and operates the spacecraft.

For more information, visit the MESSENGER Web site at
messenger.jhuapl.edu .