The first mission designed to orbit the planet Mercury is working toward a launch in May 2004.

MESSENGER was originally scheduled to lift off next March. In late August, however, mission managers recommended to NASA that MESSENGER aim for its backup launch date, after late deliveries of key subsystems and greater-than-expected technical difficulties had affected the spacecraft's assembly and testing schedule. NASA recently concurred with the recommendation.

Engineers remove a special device from one of the Star Tracker cameras that simulates the sky.

"A May launch date allows us to put MESSENGER through a full series of rigorous prelaunch tests and simulations," says Dr. Sean C. Solomon, MESSENGER's Principal Investigator, from the Carnegie Institution of Washington. "The mission's science plans for Mercury remain unchanged, and our team looks forward to exploring as planned the least understood planet in the inner solar system."

MESSENGER's mission profile includes a 12-day launch window that opens May 11, 2004; three flybys of Venus and two flybys of Mercury; and a yearlong orbital study of Mercury that starts in July 2009 - three months later than the original arrival date. Details of MESSENGER's mission design are available on the MESSENGER Web site.

A backup launch opportunity also exists in late July-early August 2004.

Spacecraft assembly is nearing completion at The Johns Hopkins University Applied Physics Laboratory in Laurel, MD, with the expectation that prelaunch space-environment testing will begin at NASA's Goddard Space Flight Center in Greenbelt. MD, by late December. Final preparations for launch are set to begin at Kennedy Space Center/Cape Canaveral Air Force Station, Fla., in early March 2004.

Follow the progress on the live MESSENGER Web Cam as the spacecraft is built and tested at The Johns Hopkins University Applied Physics Lab.

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