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MESSENGER Mission News
MESSENGER Mission News
5 Feb 2007
(Source: Johns Hopkins University Applied Physics Laboratory)

A Day in the Life of Mercury's Orbit

MESSENGER isn't due to begin its orbit of Mercury until March 2011, but engineers and scientists at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., are already rehearsing for the year-long observation of the "swiftest planet," through a series of Day-in-the-Life (or "DitL") tests.

"The system that we"ll use for orbiting Mercury will be significantly different from what we use for cruise and flybys," explains APL"s Mark Holdridge, a member of the MESSENGER mission operations team. "These exercises put the flight team and ground systems through their paces during a realistic simulation to provide some practice for readiness, to shake down the systems and procedures, and to try to uncover flaws or areas for improvement."

The team recently completed the first test, which was based on a relatively benign orbit scenario, Holdridge explains. "This first one wasn"t meant to be a stress test -- there were no solar eclipses, no encounters of hot-pole regions, nothing that required special attention. But it allowed us to work out tools and instruments and procedures, and we learned a lot of lessons that we"ve folded into the next exercise."

The team is now building command sequences for DitL 2, which tackles a dusk-to-dawn orbit in which the spacecraft always faces the Sun while riding above the line that separates day from night. "This scenario, while still not particularly stressful, is very interesting for radio science purposes," Holdridge says. "There are times during that orbit when the Sun is between Mercury and Earth, and we can"t communicate with the spacecraft when that happens. The radio science team wants to trek through those periods."

The team will conduct several of these one-day exercises before tackling more complicated week-long scenarios. Fitting these crucial dry runs in a schedule that involves real-time monitoring of the spacecraft and preparations for the second Venus flyby in June is challenging. "It's like working in three different time zones," Holdridge says. "But we have to plan far ahead enough to work through any kinks and make sure we are ready to make the most of our stay at Mercury. We have just one year in orbit around the planet, and we want to hit the ground running."

Preview of Upcoming Venus Flyby

Preview what MESSENGER's second Venus flyby on June 5 will look like with this featured animation of the event. The mission gallery, available online at, contains a variety of images, photos, animation, and movies about all aspects of the mission -- from pre-launch preparations, to images returned from the planetary flybys, to artists' renditions of the MESSENGER spacecraft on its voyage to the inner solar system. Check back often; new materials are added as the mission progresses.

Web Profile: Robin Vaughan

Though Robin Vaughan has nearly 20 years of experience with interplanetary missions, MESSENGER has presented her with a host of new challenges. As the lead engineer for the mission"guidance and control (attitude control) subsystem, Vaughan coordinated, planned and conducted tests for spacecraft integration through launch, and now continues to monitor the craft" performance in flight. Meet Robin and learn about her critical role on the MESSENGER team at

Mercury Makes an Appearance

Mercury is the most difficult of the five bright "naked eye" planets to see from Earth. But for those living in the Northern Hemisphere, a great window of opportunity for viewing the planet is about to open. Mercury will reach greatest eastern elongation from the Sun at 18 degrees on February 7. Elongation is an astronomical term that refers to the angle between the Sun and a planet, as viewed from Earth.

The planet will be visible about 7 degrees below and to the right of Venus in the western evening sky about 40 minutes after sunset. This opportunity remains through at least March 19. Mercury will emerge at sunset two more times this year: on June 2 and September 29. On three other occasions -- March 22, July 20, and November 8 -- the planet will reach greatest western elongation and materialize in the morning sky. For a diagram of the orbits of the inner planets, as they appear today, go online to

Scholarship Applications

The annual MESSENGER scholarship competition is under way! MESSENGER team members will select three recipients based on grade point average and a short essay describing what applicants think we'll learn from the MESSENGER mission. Visit the Web site at for details and an application.
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 Aug. 3, 2004, and after flybys of Earth, Venus and Mercury will start a yearlong study of its target planet in March 2011. 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 the Discovery-class mission for NASA.
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Last Updated: 5 Feb 2007