MESSENGER Spacecraft Ready For Venus Says NASA - AeroSpace News
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MESSENGER Spacecraft Ready For Venus Says NASA

WASHINGTON - NASA's MErcury Surface, Space ENvironment, GEochemistry,
and Ranging (MESSENGER) spacecraft made its closest pass to
Venus on Tuesday, June 5, 2007. This will place the spacecraft on target
for a flyby of Mercury in January 2008. MESSENGER will be the first
probe to visit the innermost planet in more than 30 years.

Space Picture of the Boeing Delta II Launch of MESSENGER August 3, 2004.



Threading its path through an aim point 209 miles above the surface of
Venus, MESSENGER will use the pull of the planet's gravity to guide
it closer to Mercury. During this flyby, Venus's gravity will change
the spacecraft's direction around the sun and decelerate it from 22.7
to 17.3 miles per second.

"Typically, spacecraft have used planetary flybys to speed toward the
outer solar system," said Andy Calloway, MESSENGER mission operations
manager, Johns Hopkins University Applied Physics Laboratory (APL),
Laurel, Md. "MESSENGER, headed in the opposite direction, needs to
slow down enough to slip into orbit around Mercury."

This will be MESSENGER's second pass by Venus. During its first flyby
of the planet, in October 2006, no scientific observations were made.
Venus was at superior conjunction, placing it on the opposite side of
the sun from Earth, leading to a two-week radio contact blackout
between the spacecraft and its operators. This upcoming encounter
offers opportunities for new observations of Venus's atmosphere,
cloud structure, space environment and perhaps even its surface. The
spacecraft will train most of its instruments on Venus during the
upcoming encounter.

"During the flyby we'll ensure that the spacecraft and payload remain
healthy, calibrate several of the science instruments, and practice
many of the observations planned for the Mercury flybys," said Sean
Solomon, MESSENGER principal investigator and planetary scientist at
the Carnegie Institution of Washington.

The team plans to image the upper cloud layers at visible and
near-infrared wavelengths for comparison with earlier spacecraft
observations. Magnetic field and charged particle observations will
be made to characterize the solar wind interaction with Venus and
search for solar wind pick-up ions. Ultraviolet-visible and X-ray
spectrometry will permit detailed observations of the composition of
the upper atmosphere, and MESSENGER will search for lightning on the
Venus night side.

MESSENGER will join the European Venus Express spacecraft, currently
orbiting Venus, to make new observations of the Venus environment. To
understand fully how solar wind plasma affects and controls the Venus
ionosphere and nearby plasma dynamics, simultaneous measurements are
needed of the interplanetary conditions and the particle-and-field
characteristics at Venus. The combined MESSENGER and Venus Express
observations will be the first opportunity to conduct such
two-spacecraft measurements.

"By coordinating and comparing these observations, we will be able to
maximize the science from both missions and potentially learn things
that would not be revealed by one set of observations alone," said
APL's Ralph McNutt, MESSENGER project scientist.

MESSENGER is only the second spacecraft to set sights on Mercury.
NASA's Mariner 10 sailed past the planet three times in 1974 and 1975
and took detailed images of about 45 percent of the surface. Carrying
seven scientific instruments on its compact and durable composite
frame, MESSENGER will provide the first images of the entire planet.
The mission also will collect detailed information on the composition
and structure of Mercury's crust, its geologic history, the nature of
its thin atmosphere and active magnetosphere, as well as the makeup
of its core and polar materials.

Launched in August 2004, MESSENGER has completed more than 40 percent
of its 4.9-billion mile journey to Mercury, which includes 15 loops
around the sun. An Earth flyby one year after launch and a large
propulsive maneuver in December 2005 set the spacecraft on course for
the first Venus flyby in October 2006.

Next up for MESSENGER is a trio of swings past Mercury, in January and
October 2008 and September 2009. During these flybys, the probe will
map most of the planet and determine surface and atmospheric
composition. These data will be used to help plan priorities for the
yearlong orbital mission, which begins in March 2011.

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