MESSENGER Mission News                            September 16, 2009

MESSENGER Team Prepares for Third Flyby, Rehearses for Orbital Operations

In less than two weeks, on September 29, MESSENGER will fly by Mercury for
the third and final time, a maneuver key to placing the probe on a
trajectory that will enable its March 2011 insertion into orbit about
Mercury. Even as the team readies for this critical event, a parallel effort
has long been underway to prepare MESSENGER for the main event.
Since January, the team has been staging orbital operations rehearsal tests,
called week-in-the-life (WITL) tests, to try out the new procedures and
software being developed for the Mercury orbital mission. Next month, they
will wrap up the second such test, and the results of these exercises are
proving pivotal to the team's plan.
"Because no spacecraft has orbited the planet Mercury before, we do not have
any direct experience planning and scheduling science observations in such
an environment," explains Alice Berman, MESSENGER's Payload Operations
Manager. "Therefore, a comprehensive orbital operations readiness plan is
underway to ensure that the mission's full science success criteria can be
met by the time that the nominal mission ends on 17 March 2012. The WITL
tests, meant to simulate several realistic weeks of orbital operations, are
an integral part of this overall readiness plan."
Between 2009 and 2010, the team will run at least seven WITLs covering
different weeks and orbital conditions. "It's critical to test as many
different observing scenarios and orbital conditions that will occur during
the orbital mission as possible," Berman says.
The first WITL test ran from January to April. The team chose to rehearse
the planning and scheduling for a week in mid-October 2011, when the level
of instrument commanding is not extremely demanding. The focus of WITL-1
was primarily on new procedures and software that had recently been
developed. "We wanted to walk through all the processing steps of preparing
a weekly command load, with careful attention to the newly developing
software tools," Berman recounts.
At an all-day workshop in February, the instrument teams worked through the
required steps for preparing and delivering their WITL-1 instrument
sequences to the mission operations team. The mission operations team then
built the spacecraft command load - adding the necessary spacecraft
commanding (e.g., solar array commanding, spacecraft downlinks) - and ran it
on the MESSENGER hardware simulator. With that done, the mission operations
and science operations teams reviewed the results.
A debriefing meeting was held in April to review the success of the test and
gather the issues to be addressed and lessons learned prior to starting the
next rehearsal test. "We learned that we need to have an extremely easy and
efficient process, because we must start a new command load each week,"
Berman explains. "We need a way to automatically keep track of status and
approvals and to notify team members when their attention or action is
needed. We found a project management software called JIRA that will help
us do all this. We learned a lot about what our current tools can do (and
what they cannot), and we are prioritizing the required software fixes and
enhancements now."
The second WITL test began in July 2009 and will be completed in October.
"In addition to testing the improved the orbital planning processes and
software, WITL-2 is focusing on a different timeframe of the orbital
mission, so that different instrument and spacecraft components will be
tested," Berman says. "Right now the mission operations team is building the
WITL-2 integrated command load, and then it will be tested on the MESSENGER
hardware simulator."
The remaining WITL tests will be conducted in 2010, and the team is
currently developing the schedule and scope of these tests. "In 2010, the
WITL tests will overlap in time so that the teams can exercise the process
of working on more than one weekly command load at one time," Berman notes.
"We will carefully assess what works well and what does not, and we will
update our processes and software tools with the lessons learned from each
WITL test."
"Once in orbit, our near-term scheduling strategy will be to prepare and
upload a new command load (containing both instrument and spacecraft
instructions) once per week," Berman adds. "This work will require the close
coordination of both the science and mission operations teams. We believe
that it will take approximately three weeks to prepare each command load, so
the science and mission operations teams will be working on more than one
command load at any given time."

On Target for Mercury Flyby 3

The MESSENGER spacecraft will pass 228 kilometers (142 miles) above
Mercury's surface on September 29 for the mission's third flyby of the Solar
System's innermost planet (http://messenger.jhuapl.edu/mer_flyby3.html). 
The MESSENGER team has been working on the flyby observation plans for months. 
Three of the highlights for MDIS include:

	NAC approach mosaic. This mosaic will provide the first close-up
images of a portion of Mercury's surface by spacecraft. (That portion of the
surface appears as a featureless white strip near the limb of the planet in
the top image.)
	WAC and MASCS targeted observations. Unlike the neatly arranged
rows and columns of most MDIS mosaics, for these observations WAC images in
11 color filters will be acquired as MASCS collects high-quality spectral
measurements of specific targets of interest. Visit this page to learn more
about these targeted observations.
	NAC departure high-resolution southern hemisphere mosaic. This
large 15-column by 13-row mosaic will provide new detail for an area of
Mercury's surface in the southern hemisphere and will be complementary to a
high-resolution mosaic of the northern hemisphere obtained during Mercury
flyby 2.

On September 23, NASA will host a media teleconference previewing the flyby.
Details of that event will be posted online at
http://messenger.jhuapl.edu/news_room/index.php.