September 16, 2009

Team Prepares For MESSENGER’s Third Flyby

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. 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.