http://messenger.jhuapl.edu/webcam/annotatedimages/annotated-20040719.html

MESSENGER Mission News
July 20, 2004

Next Stop: The Launch Pad

The MESSENGER spacecraft is now firmly attached to the third stage of its Delta II launch vehicle. In this week's Webcam image, the spacecraft is being carefully lowered onto the Delta's third stage, in anticipation of the launch period that opens at 2:16 a.m. (EDT) on August 2. MESSENGER is attached to the rocket with a two-piece clamp band (also known as a Marmon clamp) and will detach when the spacecraft is launched and on the way to its first planetary flyby.

The Delta II 7925-H (heavy lift) model is the largest allowed for NASA Discovery-class missions. It features a liquid-fueled first stage with nine strap-on solid boosters, a second-stage liquid- fueled engine and a third-stage solid-fuel rocket. With a propellant made mainly of ammonium perchlorate, the third stage provides the final boost (nearly 15,000 pounds of thrust) that sends MESSENGER into its heliocentric (Sun-centered) orbit - and on track to return to Earth for a flyby next summer. After the rocket's fuel is spent, a pyrotechnic "bolt cutter" drives a blade through the 5/16-inch diameter bolts that secure the clamp band, releasing the spacecraft.

The next major activity is the encapsulation of the spacecraft and third stage in a "can" for the 22-mile trip to the launch site on a wheeled transporter. Because the transporter must make the journey at only 5 miles per hour, the trip will be done at night when roads can be closed. When the transporter arrives at the launch pad, the can will be hoisted to the top and the third stage and spacecraft assembly will be attached to the Delta II rocket.