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Three Days to Mercury!
Three Days to Mercury!
11 Jan 2008
(Source: Johns Hopkins University Applied Physics Laboratory)

The countdown to the first flyby of Mercury by the MESSENGER spacecraft has begun. Sunday morning, MESSENGER will start recording the evidence of this historic event. At 8 a.m. EST on January 13 -- 30 hours before the closest approach to Mercury -- the spacecraft will turn its main antennas away from Earth and automatically begin executing the 5,000 on-board stored commands.

"The entire instrumentation suite will be operating during this flyby, taking more than 1,200 images and gathering other scientific observations, filling the on-board data recorder with more than 700 megabytes of history-making measurements, within a period of 55 hours," said MESSENGER Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. "Fifty minutes prior to closet approach, signals from the spacecraft will go quiet as MESSENGER passes behind Mercury, out of Earth's view. Forty-eight minutes later, engineers and scientists on the ground will attempt to witness the gravitational pull of the planet first-hand by re-acquiring the transmitted signal from the spacecraft within minutes of the closet approach point."

On Tuesday, January 15, at noon EST, 22 hours after the flyby, MESSENGER will take one last look at Mercury before turning back to Earth to start returning the treasures stored on-board. "Complicating this sequence of events is the demanding requirement to conduct all observations by the spacecraft behind the safety of MESSENGER's sunshade," Finnegan said. "Conducting this encounter at 30 million miles from the Sun, almost two-thirds closer than the Earth, would have been impossible in the era of Mariner 10. But thanks to advances in material sciences, MESSENGER's electronics and sensitive instruments can run at room temperature behind the sunshade, while the front surface temperature rises to more than 600? F."

Notwithstanding the operational and scientific importance of this flyby, MESSENGER is only slightly more than halfway along its six-and-one-half year, 4.9 billion-mile journey between its launch in August 2004 and orbit insertion around Mercury in March 2011. "Over the next 12-month period, the MESSENGER team will engage in the most grueling year of operations since launch, executing two planetary encounters, two deep space maneuvers, and possibly six additional maneuvers -- using the smaller thrusters of the on-board propulsion system -- to keep the spacecraft on course," added Finnegan.

The primary goal of this flyby is to obtain a gravity assist from the planet, which will reduce the arrival velocity of the spacecraft for orbit insertion in March 2011. "Slowing the spacecraft by 5,000 miles per hour, MESSENGER's orbital period around the Sun will be decreased by 11 days, thus setting up a planetary car race with Mercury," Finnegan said. "Using its internal engine and future gravity assists, the spacecraft, after being lapped by Mercury many times in this race around the Sun, will ultimately match the 88-day orbital period of the innermost planet."

To facilitate this change in velocity, the spacecraft will speed over the uncharted surface of Mercury at a relative velocity of more than 16,000 miles per hour and pass within 124 miles of the surface, the closest any man-made object has been to this planet.  During this close approach, the spacecraft will experience a period of 14 minutes without solar power, where operations will rely only on the spacecraft's internal batteries.


New Optical Navigation Image of Mercury Available

MESSENGER continues to speed toward Mercury, preparing for its closest approach to the planet on Monday, January 14, 2008, at 19:04:39 UTC (2:04:39 pm EST). This image was snapped with the Narrow Angle Camera, one half of MESSENGER's Mercury Dual Imaging System (MDIS), on January 10, 2008, when MESSENGER was less than 2 million kilometers (1.2 million miles) from the planet. Mercury is about 4,880 kilometers (3,030 miles) in diameter, and this image has a resolution of about 50 kilometers/pixel (31 miles/pixel).

As the spacecraft continues toward closest approach, additional information and features will be available online at http://messenger.jhuapl.edu/mer_flyby1.html, so check back frequently. Following the flyby, be sure to check back to see the latest released images and science results!


An Ode to MESSENGER's First Mercury Pass

Stuart Atkinson, a writer and amateur astronomer from the Lake District of England, has written a poem, "The MESSENGER Approaches," to commemorate MESSENGER's first flyby of Mercury. Atkins is the author of six children's astronomy books - with more to be published this year. He is also the secretary of the Cockermouth Astronomical Society, which he founded 10 years ago, and is a regular commentator on BBC Radio Cumbria's Friday evening show.


Farewell to a Fellow Explorer

The MESSENGER team notes with sadness the passing earlier today of Sir Edmund Hillary, who with Tenzing Norgay climbed to the summit of Mount Everest for the first time in 1953.  "We have lost one of the world's great explorers," offers MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "But we take some comfort in that fact that we are poised nearly on the eve of exploring huge portions of the surface of one of Earth's neighboring planets that have never before been seen at close range. Clearly the spirit of exploration that Hillary and Norgay epitomized lives on today."


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 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 this Discovery-class mission for NASA.
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Last Updated: 11 Jan 2008