NASA's MESSENGER spacecraft, the first Mercury orbiter, has arrived in Florida after being shipped from NASA's Goddard Space Flight Center in Greenbelt, Md. MESSENGER - short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging - will be launched on a six-year mission aboard a Boeing Delta 2 rocket on May 11.

Artist's impression of the MESSENGER spacecraft in orbit at Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Secured in an air-conditioned transportation van, MESSENGER arrived at the Astrotech Space Operations processing facilities near Kennedy Space Center, where it was offloaded and taken into a high bay clean room.

After the spacecraft is removed from its shipping container by employees of the Johns Hopkins University Applied Physics Laboratory, builders of the spacecraft, their first activity will be to perform an initial state-of-health check. Then processing for launch can begin including checkout of the power systems, communications systems and control systems. The thermal blankets will also be attached for flight.

A major milestone will occur in mid-April with the installation of the two solar arrays, which will then undergo a deployment test. MESSENGER would then be ready for loading of the on-board hydrazine fuel and nitrogen tetroxide oxidizer used for propulsion and spacecraft control. The fully assembled and fueled spacecraft will undergo spin balance testing in preparation for a stable cruise toward Mercury.

Finally, MESSENGER will be hoisted atop the Delta upper stage, the solid propellant Star 48 third stage booster made by Alliant which will propel the spacecraft from earth orbit on its interplanetary trajectory. After a final integrated functional test, MESSENGER will be ready to be installed into its transportation canister for the 15-mile trip to the launch pad at Cape Canaveral Air Force Station.

Meanwhile, at Space Launch Complex 17, the build-up and checkout of the Boeing Delta 2 Heavy expendable launch vehicle will be underway. The activity on Pad 17-B is currently scheduled to begin on March 31 with the erection of the first stage. The nine extra-large, strap-on solid boosters will follow, erected in sets of three during the week of April 1-7. Next, the second stage will be hoisted atop the first stage on April 13.

After the Delta 2 is fully erected on the pad, vehicle electrical checks will begin. A countdown test with the first stage loaded with liquid oxygen will occur on April 21. A Simulated Flight Test, a plus count, will occur the following day. This activates the electrical and mechanical flight systems on the vehicle as they will occur from liftoff through spacecraft separation.

Finally, on April 27, the compact 1.2-ton MESSENGER spacecraft will arrive at the pad and be lifted atop the Delta 2. After a critical integrated test, the Flight Program Verification on April 30, the fairing will be placed around the spacecraft on May 4.

The final pre-launch preparations and countdown activities begin three days before launch. Liftoff is targeted for the opening of a 12-second launch window at 2:26 a.m. EDT on Tuesday, May 11.

MESSENGER will fly past Venus three times and Mercury twice before starting its year-long orbital study of Mercury in July 2009. The Venus flybys, in November 2004, August 2005 and October 2006, will use the planet's gravity to guide MESSENGER toward Mercury's orbit. Mercury flybys in October 2007 and July 2008 will fine-tune the MESSENGER path and allow the spacecraft to gather data critical to planning the mission once it is in orbit.

MESSENGER is the next launch in NASA's Discovery Program of lower cost, highly focused missions for NASA's Office of Space Science. Government oversight of launch preparations and the countdown management of launch day is the responsibility of NASA's John F. Kennedy Space Center. The launch service is provided to NASA by Boeing Launch Services.