A suited worker checks fuel tanks before spacecraft propellant loading of the MESSENGER spacecraft seen in the background.

A suited worker at Astrotech Space Operations in Titusville, Fla., checks fuel tanks before spacecraft propellant loading of the MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) spacecraft (seen in the background). Liftoff of MESSENGER aboard a Boeing Delta II Heavy rocket, bound for Mercury, is scheduled for Aug. 2. The spacecraft is expected to reach orbit around the planet in March 2011. MESSENGER was built for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.