[meteorite-list] MESSENGER Adjusts Its Orbit around Mercury

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 15 Jun 2011 16:01:47 -0700 (PDT)
Message-ID: <201106152301.p5FN1lG8002203_at_zagami.jpl.nasa.gov>


MESSENGER Mission News
June 15, 2011

MESSENGER Adjusts Its Orbit around Mercury

The MESSENGER spacecraft successfully completed its first
orbit-correction maneuver today to reset its periapsis altitude - the
lowest point of MESSENGER's orbit about Mercury relative to the planet's
surface - from 506 kilometers to approximately 200 kilometers.

MESSENGER was 198 million kilometers (123 million miles) from Earth when
the maneuver began at 3:40 p.m. EDT. Mission controllers at The Johns
Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.,
verified the start of the maneuver about 10 minutes, 58 seconds later,
when the first signals indicating spacecraft thruster activity reached
NASA's Deep Space Network tracking station outside Goldstone, California.

This is the first of five maneuvers planned for the primary orbital
phase of the mission to keep orbital parameters within desired ranges
for optimal science observations. The spacecraft's main rocket engine
fired for only 15 seconds of the total maneuver duration of 2 minutes
and 52 seconds. MESSENGER's orbital velocity was changed by a total of
28 m/s to make the corrections essential for continuing the planned
measurement campaigns.

"The orbit that the spacecraft follows around the planet slowly changes
as time goes by," explained APL's James Hudson, lead guidance and
control engineer for the MESSENGER mission operations team. "Because of
Mercury's proximity to the Sun and MESSENGER's highly eccentric orbit,
solar gravity has a strong effect on the spacecraft's orbit,
particularly periapsis altitude."

MESSENGER Mission Systems Engineer Eric Finnegan, of APL, said that the
team was well prepared for the maneuver and everything proceeded as
expected. "Initial data from the burn indicate nominal maneuver
execution. MESSENGER's orbital trajectory around Mercury has now been
reset to continue our in-depth exploration of the innermost planet."

MESSENGER Completes First Mercury Year in Orbit

On June 13, MESSENGER completed its first Mercury year (88 Earth days -
the time it takes Mercury to make one revolution around the Sun) in
orbit about the innermost planet. The spacecraft has three more Mercury
years to go during the primary science phase of the mission.

The spacecraft celebrated this milestone at the tail end of a four-day
superior solar conjunction - the tenth since launch - during which the
spacecraft was on the opposite side of the Sun from Earth. Throughout
that time, reliable communication between the spacecraft and mission
operators at APL was not possible because of interference from the Sun's
hot plasma, but telemetry received once MESSENGER came out of
conjunction on June 14 confirmed that the spacecraft and all of its
systems continue to operate nominally.

MESSENGER's instruments are providing a wealth of new information about
the planet closest to the Sun. Tens of thousands of images of major
features on the planet - previously seen only at comparatively low
resolution - are now available in sharp focus.

Measurements of the chemical composition of Mercury's surface are
providing important clues to the origin of the planet and its geological
history. Maps of the planet's topography and magnetic field are
revealing new clues to Mercury's interior dynamical processes. And
regular detections of energetic particles are providing insight into the
workings of Mercury's magnetosphere.

MESSENGER team members will be discussing these new findings in a news
conference <http://messenger.jhuapl.edu/news_room/details.php?id=171> at
NASA Headquarters on June 16, 2011, at 1 p.m. EDT,
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
entered orbit about Mercury on March 18, 2011, to begin a one-year study
of its target planet. 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.
Received on Wed 15 Jun 2011 07:01:47 PM PDT

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