The space agency's rover, dubbed "Opportunity," needs the little extra kick in speed the bigger boosters provide so it can keep up with its twin probe "Spirit," which was launched toward Mars on June 10 and is doing well so far.Together the $800 million exploration program will seek out answers to questions involving when -- not if -- water existed on Mars and how long it was around.
"These missions are not designed to find life on Mars. They're not designed to find water on Mars," said Ed Weiler, NASA's space science chief in Washington, D.C. "What we don't know is how long this water persisted at any given place and how long it stayed there."
Bigger boosters
Built by Minnesota-based Alliant Techsystems, the larger booster rockets originally were designed for the Delta 3, a launcher that Boeing has flown three times and seen two failures. The solid-fueled motors worked well each time and did not cause either mishap.
The Delta 2, meanwhile, is considered a workhorse rocket and is well proven with a solid reputation. Combining the Delta 3's boosters with a Delta 2 resulted in the Delta 2 Heavy.
First discussed in 1995, with hardware development beginning in 1998, the Delta 2 Heavy allows NASA to launch spacecraft that are too heavy for a standard Delta 2 yet doesn't require the significantly more capable -- and more expensive -- Delta 4.
So although all the parts of this rocket have flown successfully before, Saturday's planned launch is the first time these components have been combined together.
To accommodate the larger motors, changes were made in the Delta 2 that included beefing up the first stage body, moving the forward attach point for the boosters higher up on the rocket and making minor changes to the shape of the motor's nosecones.
Most of the design and development work involved studies of every kind, including the way the rocket's aerodynamics would change with the taller motors on its first stage, said Kris Walsh, Boeing's director of NASA programs for Delta.
"NASA has asked Delta to do a lot for it. In the last five years we have done many, many upgrades for NASA," Walsh said. "From longer fairings for Aqua to new upper stages for Deep Space. And we go through the same process each time."
First flight jitters
That makes officials feel better but doesn't erase the normal worries associated with every new rocket before its first flight.
"It's been looked at with a fine tooth comb. We're real confident in this flight," said Omar Baez, NASA's director of Expendable Launch Vehicles at Kennedy Space Center.
"There's been intensive reviews. There's been senior panels of senior engineers that Boeing brought on to just look over and make sure all of our processes were in line to make this a safe flight the first time out of the box," Baez said.
The solid rocket boosters used on Delta rockets are made of a composite material known as graphite epoxy, and are known as GEMs -- short for Graphite Epoxy Motors. A number after the acronym tells how big the motor's diameter is, expressed in inches.
A GEM 40 is used on the Delta 2 and is 40 inches in diameter and 32 feet in length. It burns for about 64 seconds.
The Delta 3 and Delta 2 Heavy relies on the GEM 46, which is 46 inches in diameter and 36 feet in length. It burns for about 75 seconds and produces about 30,000 pounds more thrust than the GEM 40.
Six of the nine GEMs are ignited when the Delta rocket still is on the ground, and the remaining three are ignited in the air just after the first six burn out. Spent boosters are then jettisoned to fall into the ocean.
The GEMs are not recovered and reused. They often turn up in fishing nets or wash up on shore along Florida's Space Coast or Atlantic islands.
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