NASA 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.