[meteorite-list] MESSENGER Kicks Off Yearlong Campaign of Mercury Science

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 5 Apr 2011 12:23:52 -0700 (PDT)
Message-ID: <201104051923.p35JNqgc024208_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/details.php?id=166

MESSENGER Mission News
April 4, 2011

MESSENGER Kicks Off Yearlong Campaign of Mercury Science

This afternoon, MESSENGER began its yearlong science campaign to
understand the innermost planet. The spacecraft will fly around Mercury
700 times over the next 12 months, and its instruments will perform the
first complete reconnaissance of the cratered planet's geochemistry,
geophysics, geological history, atmosphere, magnetosphere, and plasma
environment.

"MESSENGER's orbital commissioning phase, which we just completed,
demonstrated that the spacecraft and payload are all operating
nominally, notwithstanding Mercury's challenging environment," says
Principal Investigator Sean Solomon, of the Carnegie Institution of
Washington. "With the beginning today of the primary science phase of
the mission, we will be making nearly continuous observations that will
allow us to gain the first global perspective on the innermost planet.
Moreover, as solar activity steadily increases, we will have a front-row
seat on the most dynamic magnetosphere - atmosphere system in the Solar
System."

MESSENGER's 12-month orbital phase covers two Mercury solar days (one
Mercury solar day, from sunrise to sunrise, is equal to 176 Earth days).
This means that the spacecraft can view a given spot on the surface
under given lighting conditions only twice during the mission, six
months apart, making available observation time a precious resource. "So
the surface mapping observations had to be planned for the entire year
far in advance to ensure coverage of the entire planet under acceptable
illumination and viewing geometries," says MESSENGER Deputy Project
Scientist Brian Anderson, who oversaw the planning for orbital operations.

SciBox - a suite of software tools for science observation simulation -
was developed to help the team choreograph the complicated process of
maximizing the scientific return from the mission and minimizing
conflicts between instrument observations, while at the same time
meeting all spacecraft constraints on pointing, data downlink rates, and
onboard data storage capacity. The SciBox tool simulates the entire year
of science observations and identifies the best times to take each type
of observation. The commands for each week of observations are derived
from this full mission analysis.

For instance, Anderson explains, "The remote sensing instruments to
measure topography and determine surface and atmospheric composition are
fixed on the spacecraft and share the same view direction. Because the
ideal viewing directions for these instruments are not the same, we
assigned altitude ranges for which the spacecraft pointing is optimized
for the science from each instrument. "The camera has its own pivot, so
it has much greater freedom in viewing the surface and it takes pictures
at all altitudes," he continues. "Several other instruments make
measurements of local properties, magnetic field, or charged particles
and acquire excellent data regardless of the spacecraft pointing."

SciBox works by finding the best opportunities for each of the
instruments to make their measurements and then analyzing how those
measurements contribute toward the science goals of the entire mission.
"The SciBox tool allows us to plan thousands of science observation
activities every week that have to be precisely timed with customized
spacecraft pointing," Anderson says.

The observations depend critically on where the spacecraft is in its
orbit around Mercury, so the final science observation plan was not
generated until the MESSENGER spacecraft completed Mercury orbit
insertion. The software commands for this week's instrument operations
were sent to MESSENGER only last week.

"We had to wait until after MESSENGER was in orbit before we could start
building the actual science sequences that start today, because we
needed the actual in-orbit ephemeris as calculated by our navigation
team to ensure that images and other pointed observations were taken
where planned," explains MESSENGER Payload Operations Manager Alice Berman.

On March 21, her team received the first ephemeris following Mercury
orbit insertion, a delivery that provided less than two weeks for each
instrument payload lead to generate inputs, test them, and deliver them
to the mission operations team. That team then had to merge those
science observation commands with the spacecraft operating commands and
fully test the entire package.

For example, the command load for this week's observations provides for
the acquisition of 4,196 images by the Mercury Dual Imaging System
(MDIS). The MDIS team had to check the commands governing each of those
images; and the guidance and control team next had to run detailed
software simulations on all the science guidance and control commands
for the entire week and then add the non-science commands, such as those
directing solar panel motions and star trackers. Finally the team
re-simulated the full sequence again.

"It's a tremendous amount of work and analysis that has to be done every
week," Berman notes. "From our experience with the In-the-Life exercises
over the last two years, we determined that we would need three weeks
for that process. But our entire team did an outstanding job getting it
all done on the accelerated schedule."

Imaging during the MESSENGER flybys provided important reconnaissance
for the observations from orbit. During MESSENGER's first six months in
orbit, MDIS will create new, higher resolution, global maps of the
planet in color and monochrome, acquired under near-ideal viewing
conditions.

Emphasis during the second six months will shift to targeted,
high-resolution imaging with the MDIS narrow-angle camera and
acquisition of a second monochrome map but from a different viewing
direction to allow stereoscopic analysis of topography. Additionally,

    * The Mercury Laser Altimeter will measure the topography of the
      northern hemisphere over four Mercury years.

    * The Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer
      will yield global maps of elemental composition.

    * The Magnetometer will measure the vector magnetic field under a
      range of solar distances and conditions.

    * The Visible and Infrared Spectrograph will produce global maps of
      surface reflectance from which surface mineralogy can be inferred,
      and the Ultraviolet and Visible Spectrometer will produce
      time-dependent global maps of exospheric species abundances versus
      altitude.

    * The Energetic Particle and Plasma Spectrometer will sample the
      plasma and energetic particle population in the solar wind, at
      major magnetospheric boundaries, and throughout the environment of
      Mercury at a range of solar distances and levels of solar activity.

    * The radio science experiment will extend topographic information
      to the southern hemisphere by making occultation measurements of
      planet radius, and the planet's obliquity and the amplitude of the
      physical libration will be determined independently from the
      topography and gravity field.

MESSENGER orbits Mercury twice every Earth day. Once a day, the
spacecraft will stop making measurements and turn its antenna toward
Earth for eight hours to send data back - via the Deep Space Network -
to the MESSENGER Mission Operations Center at the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md.

"The engineering teams accomplished an astonishing achievement by
developing, launching, and guiding MESSENGER through the inner solar
system and safely placing the spacecraft in orbit about Mercury" says
Anderson. "Now the science planning teams are working hard to take full
advantage of this unprecedented opportunity to learn everything we can
about Earth's heretofore enigmatic sibling planet. With thousands of
science observation commands to plan, test, and verify every week, not
to mention the need to verify that the observations are successful, we
certainly have our work cut out for us," Anderson says. "But we have the
tools, the people, and the processes in place to do the job. So far,
everything is going just the way we planned."

------------------------------------------------------------------------
Where is MESSENGER?

You can follow MESSENGER?s journey in its orbit about Mercury with the
newly revised "Where Is MESSENGER?"
<http://messenger.jhuapl.edu/whereis/index.php> website feature, which
offers simulated views of the spacecraft's current orbit and what
Mercury looks like from MESSENGER's current perspective. The Solar
System Simulator <http://space.jpl.nasa.gov/> offers another option for
portraying Mercury from the perspective of the MESSENGER spacecraft at
any time during the remainder of the mission. Simulated views of nearby
Mercury or distant Earth from MESSENGER may be created for a variety of
fields of view.

For complete information on MESSENGER's Mercury orbital operations, go
online to http://messenger.jhuapl.edu/mer_orbit.html.

------------------------------------------------------------------------

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 17, 2011 (March 18, 2011 UTC), to
begin a yearlong 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 Tue 05 Apr 2011 03:23:52 PM PDT