On Pad 17-B, Cape Canaveral Air Force Station, a third Solid Rocket Booster (SRB) is lifted up the mobile service tower to join the other SRBs there. They will later be mated to the Boeing Delta II Heavy rocket for the Aug. 2 launch of the MESSENGER spacecraft to the planet Mercury. The spacecraft is expected to reach orbit around Mercury in March 2011. MESSENGER was built for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.